Kitobni o'qish: «British Manufacturing Industries: Pottery, Glass and Silicates, Furniture and Woodwork.»

PREFACE

The object of this series is to bring into one focus the leading features and present position of the most important industries of the kingdom, so as to enable the general reader to comprehend the enormous development that has taken place within the last twenty or thirty years. It is evident that the great increase in education throughout the country has tended largely to foster a simultaneous interest in technical knowledge, as evinced by the spread of Art and Science Schools, Trade Museums, International Exhibitions, &c.; and this fact is borne out by a perusal of the daily papers, in which the prominence given to every improvement in trade or machinery attests the desire of the reading public to know more about these matters. Here, however, the difficulty commences, for the only means of acquiring this information are from handbooks to the various manufactures (which are usually too minute in detail for general instruction), from trade journals and the reports of scientific societies; and to obtain and systematize these scattered details is a labour and a tax upon time and patience which comparatively few persons care to surmount. In these volumes all these facts are gathered together and presented in as readable a form as is compatible with accuracy and a freedom from superficiality; and though they do not lay claim to being a technical guide to each industry, the names of the contributors are a sufficient guarantee that they are a reliable and standard work of reference. Great stress is laid on the progressive developments of the manufactures, and the various applications to them of the collateral arts and sciences; the history of each is truly given, while present processes and recent inventions are succinctly described.

BRITISH MANUFACTURING INDUSTRIES

POTTERY

By L. Arnoux, Art Director and Superintendent of Minton's Factory

Without entering into an elaborate dissertation on the antiquity of the Art of Pottery, which would be out of place in so short an article as this, I will briefly state that the practice of making vessels from plastic clays, for holding liquids and provisions, first resulted from the exertions made by man to emerge from his primary condition. It is a well known fact that vessels of clay, only partially baked, have been found, together with stone implements belonging to prehistoric times, and that those vessels, unfinished as they were, had peculiar characteristics. But supposing that this was not so, it must strike everybody that, after providing himself with those rude instruments wherewith to obtain his food and protect his life, man must have taken advantage of his power of observation to notice the property of plastic clay to retain water, and to find out to what useful purpose it might be brought for making vessels better suited to his wants, than the skins of animals or pieces of wood roughly hollowed out. If not probable, it is however not impossible, that the first man, taking in his hand a lump of soft clay, should have tried to give it a defined shape, in which case the art of pottery would be as ancient as the human race. It may have been anterior to the use of fire, for a sound and useful pottery may be made with clay hardened in the sun, as still practised in Egypt and India. At all events, it existed previous to the working of the first metal, as one can hardly understand how bronze could have been melted, without the assistance of vessels made of fired clay carefully selected. Consequently it is admitted by everybody, that this is one of the earliest of human inventions, and that the material has proved most durable. This durability, secured by the application of heat, is a very remarkable phenomenon; for while many other materials, apparently very hard, have been found unable to stand the atmospheric changes or the continuous contact with a damp soil, it was sufficient to submit this one to a very moderate heat, to be enabled to resist these various agencies for several thousands of years. This is particularly noticeable in the black Greek pottery, which, while possessing all its former appearance, can, however, be scratched by the nail or broken by a gentle pressure between the fingers. It is thus that we are indebted to the art of pottery for innumerable works of art, many of which have proved most useful in elucidating historical facts, and making us acquainted with the habits, dresses, and ceremonies of ancient peoples.

One can understand how difficult it is to decide who were the earliest potters. It is a question that archæologists have often tried to answer, but which is not likely to be ever solved. Pottery was created to meet a special want of the human race, and we find early pottery existing in almost every part of the world, in unknown America, as well as in Europe or Asia. It is, however, easier to decide which people first excelled in it, and in this respect we must give equal credit to the Egyptians and the Chinese. It is mentioned in sacred history that more than 2000 years B.C. the Egyptian potters were celebrated for their skill, and if we can believe Chinese tradition, the manufacturers in China were at this same time under the control of a superintendent appointed by the government. Unfortunately, we have very little information respecting the history of the art in China, previous to the sixteenth century; and although we have a notion of what they did and how they did it, it is wiser, with our imperfect knowledge, to abstain from speculating as to when the different sorts of Chinese ware were produced. But as regards the Egyptians, there is no uncertainty; some of their ceramic relics bear their own inscriptions, and others have been found associated with objects or monuments whose dates have been carefully ascertained. We may well believe in their skill, when we know that they were acquainted with the most difficult processes for making the bodies and glazes, and that they used the same metallic oxides for colouring their ornaments that we are now using, though often, let us acknowledge, with less success. During a period of at least eleven hundred years, from the eighteenth to the twenty-fourth dynasty, they displayed considerable ingenuity in the production of small figures, jewellery ornaments, and hieroglyphic tablets, in which several sorts of pottery mixtures and differently coloured glazes were most cleverly associated. It is from Egypt that sound principles of pottery making seem to have spread to the different nations; first to the Phœnicians, who in their turn became famous for their knowledge in the art of vitrifying mineral substances; and then to the Assyrians, who seem to have applied pottery more specially to the ornamentation of their buildings.

Greece, who shortly after received her first notions of art from the two former nations, did not devote her energies so much to improvement of material and richness of colour, as to the refined beauty of the shape and the excellence of the painting.

In pottery, the material is of little value, and it is only by the art displayed in shaping and decorating it, that its price can be increased. In this respect the Greeks proved to what enormous value it could be raised, by making it the groundwork of their art, since sums equivalent to several thousand pounds of our money were readily paid by Roman patricians for a single Corinthian vase. In this, as in the other branches of art, the recognized taste of the Greeks will never be surpassed; and if at the present time little attention is paid by collectors to their ceramic productions, it is probably owing as much to the versatility of our tastes and fancies, as to our inability of showing the articles to their advantage.

The Greeks seem to have monopolized the ceramic production of these fine works for seven or eight centuries at the least; for although vessels of the same description were largely produced in Italy, it was invariably by the Greeks, following closely the traditions and mode of decorations of their own country. It was only about a century B.C. that the Romans began to create a pottery on which they impressed their stamp, a pottery really their own; I mean that which is so improperly called Samian, and so easily known by its reddish colour and the embossed ornaments by which it is profusely covered. It is, however, genuine and characteristic, neatly executed, and possessing some standing qualities which did not belong to the Greek. On the other hand, the refinement is deficient; the forms are derived from the circle instead of the ellipse; the plain surfaces are replaced by embossments, and the painting is absent. For four centuries, the Romans seem to have made this class of pottery in several of their European settlements, chiefly in Italy and in the provinces adjoining the Rhine. In the operation they seem to have required some special material, which imparted to its bright red surface a semi-shining lustre or glaze, and which has proved remarkably durable. After this, the art of pottery experienced a time of darkness, when all the refined processes seem to have been neglected, and primitive vessels, like those produced by the Saxons, Gauls, and Celts, ranked amongst the best examples. The decorations, if any, are rudimentary; not only is the painting reduced in a few instances to some lines or spots made of a different clay, but even the embossed ornaments are replaced by lumps of clay or impressed lines in a kind of geometrical disposition. Art was not quite dead, but it scarcely breathed. However, these specimens are not altogether uninteresting, for they were the first efforts of our forefathers, and there is always a certain pleasure in witnessing the feeblest attempts made in the research of art.

But the time came when pottery was to accomplish another revolution, no less remarkable than the first. Strangely enough, it was again from the East, in nearly the same province in which it originally took its rise, that it was revived, and it is not unlikely that some faint tradition of the old processes was the source whence sprung the new ceramic era, which was to extend to our own time.

The precise date of this revival is not positively ascertained; but it was probably contemporary with the establishment of Islamism amongst the Arabs. The energy displayed by this people in improving and adapting the different fabrics to the requirements of their new religion, was no doubt beneficial to the art of pottery, and with their fanaticism and spirit of proselytism, they carried their new ideas to every country which they conquered. Syria became a great industrial centre, and some of its towns, such as Damascus, were soon famous for the perfection of their wares. To reach Europe, however, this new movement did not take its course through Greece and Italy, as in the first instance; it was through Egypt and the North of Africa that, at the beginning of the eighth century, it made its way to Spain, where it became firmly established. As regards pottery, nowhere were better specimens produced than in the towns of Malaga, Grenada, Cordova, and others, going northwards as far as Valencia and Toledo. The newest feature of the Arabian or Saracenic pottery (called Hispano-Moresco ware, when made in Spain) was the introduction of the oxide of tin in the glaze, to render it opaque. Previous to this innovation, when white was required for a design executed on a clay which did not take that colour in firing, these parts had to be covered with a silicious mixture, and subsequently coated over with a transparent glaze. This was the Assyrian and Persian process. To find a white opaque enamel, which could be applied direct on a coloured clay and adhere firmly to it, was a great discovery.

Everyone now knows how successfully these people used pottery for the ornamentation of their buildings, and how ingeniously they mixed transparent and opaque enamels to obtain an unprecedented harmony of effect. Not only did they use this tin enamel in parts, but also all over the ware, making it more or less opaque as they wished; and this was the origin of the pottery called majolica, which, according to tradition, was imported from Majorca to Italy, at the beginning of the fifteenth century, and for the introduction of which credit is given to Lucca Della Robia. Terra in-vitriata was the first name given by this sculptor to his works, when they were coated with this opaque mixture. There was at that time such an earnest desire to find suitable materials for art decorations, that the new enamels soon ceased to be exclusively applied to architectural purposes. Under the beneficial influence of the revival of taste for ancient art, and the encouragements with which it met from the princes at that time ruling the Italian Republics, majolica attained its beauty, though its external appearance reminded us but little of its Spanish or Oriental origin. During the course of the fifteenth and sixteenth centuries, the most famous in the history of modern art, the influence of the great painters of that period was soon felt by those whom we may call the artists of pottery, for the name of potters could hardly do them justice; and several of them applied their talents to the reproduction, on that ware, of their most celebrated paintings. It was reported that Perugino, Michael Angelo, Raphael, and many others painted majolica ware, probably on account of their cartoons being often reproduced; and it is sufficient to say that such talented men as Francisco Xanto da Rovigo, Orazia Fontana, and Georgio Andreoli, devoted their energies to the improvement of this branch of art. Most of the Italian towns had their manufactory, each of them possessing a style of its own. Beginning at Caffagiolo and Deruta, they extended rapidly to Gubbio, Ferrara, and Ravenna, to be continued to Casteldurante, Rimini, Urbino, Florence, Venice, and many other places.

After the sixteenth century, majolica soon degenerated in appearance and quality, the producers being more anxious to supply the market, than to devote to their ware the care and attention bestowed on it by their predecessors. In increasing the quantity of tin in their enamel, to make it look more like porcelain, they impoverished their colours, and this alteration, however prejudicial to majolica, assisted greatly in the new transformation which it was subsequently to undergo. It was under the name of faïence that it continued to be known, and France and Holland became the principal centres of its manufacture. At Nevers, it still resembled slightly the Italian ware, though at Delft, in Holland, it was principally made to imitate the blue and white ware of the Chinese, in which attempt the makers were often remarkably successful. At Rouen, the blue ornamentation was relieved with touches of red, green, and yellow; at Moustiers, the monochrome designs were light and uncommonly elegant; at Paris, Marseilles, and many other places, the flower decoration of the old Sèvres and Dresden ware was imitated with a freedom of touch and a freshness of colour which is really charming. This pottery, which was a great favourite in the seventeenth and eighteenth centuries, declined rapidly soon after our present earthenware made its appearance; the chief inducement for the change, on the part of the manufacturers, being the excessive price of tin, which is the principal ingredient of enamel.

Except in the provinces contiguous to France, Germany was never a producer of majolica. It created, however, a pottery entirely of its own, full of originality in its general appearance, and which, by the peculiarity of the process, was really a very distinct type. I am alluding to the Flemish and German stoneware. There is a tradition, that the first pieces were made in Holland at the very beginning of the fifteenth century. The principal centre of its production was, however, in Germany, at Nuremberg, Ratisbon, Bayreuth, Mansfeld, and other places; but the best were made in the neighbourhood of the Lower Rhine, where the clays most fitted for that class of pottery were easily to be found. Here we find, for the first time in Europe, the body of the ware partly vitrified by the high temperature to which it was submitted, and also the remarkable peculiarity, that it was glazed by the volatilization of common salt, thrown into the oven when the temperature had reached its climax. The combination of these two processes had never been effected before, and it would be difficult on that account to find any connection between stoneware and some of the Egyptian potteries. This stoneware varied in colour: some were almost white, some brown, others of a light grey, the last being the most valuable when the effect was increased by blue or purple grounds, harmonizing admirably with the foundation colour of the ware. The shapes are generally elaborate, with a great many mouldings, enriched with embossed ornaments in good taste, some of which were designed by no less an artist than T. Hopfer. The decline of this stoneware began with the seventeenth century, and from that time to the present, this material was only used for wares of the commonest kind. It is only very lately, that it was revived successfully by Messrs. Doulton and Co., of Lambeth.

France, which had not as yet any ideas about the process for imitating the Italian majolica, created towards the same time two new sorts of pottery, one of which is the Palissy ware, the other the faïence d'Oiron. Palissy, a very inquisitive and intelligent man, is said to have been possessed by a strong desire to reproduce some Italian ware, which he had the opportunity of seeing; whether it was a piece of majolica or of graffito, is not known. Left to his own resources – for there was nobody to instruct him – he succeeded by perseverance and industry in finding out the process for making the different coloured glazes that the Moors had used long before him. There was no discovery in this, but the talent which he displayed in the mixing and blending of these vitreous colours, combined with the incontestable originality of his compositions, have made this ware very difficult to imitate.

The time of its production was limited to the life of Palissy, for there is not really a single good piece which can be traced to his successors. In the faïence d'Oiron, incorrectly called Henri Deux ware, we find a real cream-coloured earthenware taking precedence of two hundred years over our own. It was made between the years 1524 and 1567, and we have now every proof that three persons co-operated in this invention: Heléne de Hangest, who had been formerly entrusted by François I. with the education of his son, afterwards Henry II.; her potter at Oiron, named François Charpentier; and her secretary Jehan Bernart. The charming pieces resulting from the combination of these three intellects were few, and only intended to be offered as presents to the friends of the noble lady at court. This sufficiently explains the monograms and devices, which are found associated with the elaborate ornaments profusely spread over their surface. No ware was ever made before or after this, which required more care and delicate manipulation, and this explains why the highest prices paid in our generation for an article of pottery have been freely given for several of these curiosities. Their principal feature consists in inlaying differently coloured clays one into the other, a process not quite new, as it had been extensively used in mediæval times for making encaustic tiles for the flooring of our churches, but they were so minutely and neatly executed, and the designs so well distributed, that they are justly considered as marvels of workmanship. In speaking of these faïences d'Oiron, we can hardly admire sufficiently the variety in the productions of this period of the Renaissance; and if we select four of these specimens, such as a piece of Faenza ware, one of stoneware, one of Palissy, and another of Oiron, they may fairly stand as good illustrations of the ingenuity of man.

The progress realized in these times seems to have undergone a sort of lull, and if we accept the French and Delft faïences, which were a transformation of majolica, we find that the greatest portion of the seventeenth century was not marked by any new discovery or decided improvement. Towards its close, however, we begin to notice in Germany and the western countries of Europe several attempts at making a ware, possessing the three standard qualities of whiteness, hardness, and transparency of the Chinese, and these were the precursors of the great movement which occupied the whole of the eighteenth century. As might be expected, inquiries made in different countries by persons unacquainted with each other, brought different results; and if they failed in so much, that a porcelain identical to the Oriental was not reproduced, all of them succeeded in making a white ware of their own, adapted to the materials which they had at their disposal. And thus arose in each country the source of a prosperous trade.

It is only at that period, that England began to take her position amongst the producers of pottery, at least in a manner deserving of that name. Up to that time, if we were to judge by the quality of her work, she did not seem fitted for it, no more than for any sort of manufacture which required taste or a certain knowledge of the arts of design. In fact, it is easy to notice in looking at our collections of art manufactures, that the English samples are deficient in many respects; they may be gaudy without harmony of colour, or elaborate without refinement, exhibiting a certain amount of roughness in execution, when placed side by side with Italian, French, or German specimens of the same class. It is likely, with certain exceptions, that the Anglo-Saxon race did not feel much the want of all those niceties, and did not make great exertion to excel in the practice of those arts, for the appreciation of which its mind was not yet sufficiently cultivated. It has been remarked, that as the progress of art was constantly from East to West, the geographical position of England might account in some respects for her backwardness. However, like children of slow growth whose understanding does not seem quick or acute, but who afterwards derive the benefit of their reserved strength, England, coming almost the last in the production of pottery, seems as though she did so for maturing her capabilities. In this, as in the practice of other arts, she is slow, and her first steps are clumsy. Experimenting for some time, with mixed or indifferent success, she seems to hesitate, till she begins to feel that she holds the thing in her grasp, and then the day soon comes when she teaches the world what she can make of it. We can scarcely give her credit in the preceding review for some Staffordshire pottery made with the yellow or red marl, thickly glazed with the galena extracted from the Derbyshire mines, the decoration of these pieces being effected by pouring the light clay on the dark one in a symmetrical manner. This pottery was in use from the time of Queen Elizabeth down to the year 1775, the date of the latest specimen that I have seen. Some pieces preserved in the British Museum, in the Museum of Geology, and in M. Solon's collection, are to be noticed for their quaintness.

Up to the eighteenth century, no other clays than those extracted from the coal measures seem to have been used in Staffordshire; and the advantages derived from an abundant supply of both clay and fuel must have powerfully contributed to the settlement of this industry in that county. In Shaw's 'History of the Staffordshire Potteries,' which with Plot's 'History of Staffordshire,' are the only books to afford information on the then state of this trade, and whose most interesting extracts have been given by Sir Henry de la Beche in his excellent catalogue of the pottery exhibited in the Museum of Practical Geology, we gather this fact, that so far back as 1661, an Act of Parliament regulated the dimensions and quality of earthen vessels manufactured at Burslem, for holding the butter brought to the markets.

Towards 1680, a radical change seems to have taken place in the way of making the ware, by substituting common salt for the galena in the glazing process. This new production was called crouch ware, and there is every probability that the substitution was first made by a person acquainted with the manufacture of the German and Flemish stoneware, which at a former period had been tried in England. At that time Burslem possessed twenty-two ovens, and Shaw says, that when these were at work, the vapours emanating from the salt were such as to produce a dense fog in the town. These assertions leave no doubt as to the date of the commencement of this manufacture in Staffordshire, and that Burslem was its first seat.

Two German brothers, of the name of Elers, who settled near this town in 1688, seem to have been the first to try to produce pottery of a better class than the crouch ware. Their first attempt resulted in the production of a well finished red stoneware, which probably resembled the red ware made in Saxony by Bottger at the same time. Those who have left any written information about it, say that for general appearance and careful execution, it was quite equal to any similar article made by the Chinese; but I must confess, that the specimens that I had the opportunity of seeing are rather porous and far from being highly baked. These foreigners paid also great attention to the improvement of the white ware, and they were the first to employ the plastic clay from Dorsetshire for the purpose of whitening the cane marl of the locality. Their ware was generally light and well-shaped, and though the plaster moulds were wholly unknown at the time, and were only introduced fifty years later, the impressions taken from metal moulds are neat, and show the ornaments standing sharply out from the surface. This, combined with the peculiar appearance given to the surface by the sublimation of the salt, and its light colour, are the principal feature of the Burslem ware, which continued in existence till 1780, although before that date more perfected articles had found their way to the market. The brothers Elers used to make a great secret of their mixtures, and left the district as soon as the other manufacturers became acquainted with them. Astbury, who had been instrumental in robbing them of their processes, was one of the most intelligent amongst these potters, and it was he who, in 1720, introduced the flint, calcined and ground, for whitening the body of the ware, one of the greatest improvements in the making of earthenware. He seems to have been a thoughtful and persevering man, and it is said that the idea of this new material was suggested to him, by seeing a shoeing smith calcining a flint, for the purpose of blowing the dust into the eyes of his horse, suddenly afflicted with a kind of blindness. This is probably only a fiction, as the idea must have originated from witnessing the change undergone by flint when brought to a red heat.

As the pottery trade was taking root in the district, it is no wonder that we find many intelligent manufacturers doing their best to improve it and make it profitable. Eminent amongst them was Josiah Wedgwood, whose name as a potter is never likely to perish. For particulars concerning his private life, trade, and manufacture, there are two excellent books, by Miss Meteyard and Mr. Llewellyn Jewitt, in which every matter of interest about him has been carefully entered. Born at Burslem, in 1730, of a family of potters, he began by serving his apprenticeship as a thrower under his brother, and must have settled in business very early, as he had had already two partners when he set up on his own account, in 1759, being then only twenty-nine years of age. His first attempts seem to have been directed to making a green ware, that is, a white ware covered with a glaze of that colour, which he succeeded in getting particularly bright; and also to the tortoiseshell, which had its surface mottled with glazes differently stained, and which, by their blending when they are fused in the oven, present some analogy with the works of Palissy.

One of Wedgwood's decided successes was, perfecting the white cream-colour ware, which was so superior to anything done before, that it commanded at once a great sale at home and abroad. Queen Charlotte admired it much, and, in consequence of her patronage, it took the name of Queen's ware, under which it was known for a long time. It is light, of a pleasing colour, elegantly shaped, and in the hands of artists has proved an admirable material to paint upon.

It would take too long to enumerate all the improvements which Wedgwood effected in his trade in the second half of the last century, but I must mention as prominent amongst his works, the black Egyptian and jasper wares, in making which he had no assistance whatever, and which constitute two new and perfect types in pottery. From Wedgwood's origin and early labours, it is easy to guess that his instruction must have been limited; but he was a clear-minded and inquiring man, possessing that sort of intuition by which he could easily understand things, which in other people would have required preliminary studies; besides, he had a natural taste for art and a systematic way of going through his experiments, which were sure to bring them to a successful issue. It was his good fortune to be assisted by two men of superior intelligence, viz. Flaxman, the sculptor, who designed many of his shapes, and modelled for him an almost innumerable number of subjects for slabs and cameos; and Thomas Bentley, a distinguished scholar, with whom he was commercially connected, and whose knowledge of art he found of great utility.

GLASS AND SILICATES

By Professor Fredk. S. Barff, M.A

The very brilliant and useful substance, which forms the subject of this article, is said to have been discovered by the Phœnicians. The story goes that some Phœnician merchants, while cooking their food on the sands near the seashore, noticed that the ashes of the plant, with which they made their fire, caused some of the sand to melt and form a vitreous substance; but whether this tale be true or not, it is well known that for a long time these people made glass from the materials which were abundant on their sea and river coasts.

Glass, however, was produced long before this by the Egyptians for the beads and ornaments used in adorning their mummies, and many specimens of these are in the British Museum. It is certain also that they well knew how to make certain substances impart colour to glass for the manufacture of most of these beads. The Romans made rich goblets of ruby glass, some of which are to be seen in collections in this country, as well as urns to receive the ashes of their dead, four of which, of a green colour, are also in the British Museum. The manufacture of these vessels proves that this nation was well skilled in the arts of blowing and modelling glass; and their designs, which we are now reproducing, show that they were at least not inferior in artistic skill to those who have formed their taste in this highly civilized age. We have no record of glass being used for glazing purposes in ancient times. The Venerable Bede introduced it into this country about 674 A.D., and employed it in the adornment of church windows. Ordinary window glass was made at the works in Crutched Friars in 1557, and plate glass at the large works of the Ravenhead Plate Glass Company, near St. Helen's in Lancashire. About 1776, flint glass vessels were blown at the establishment in the Savoy House; and the second Duke of Buckingham brought over Venetian artists, at that time the most skilled, to make glass for mirrors, carriage windows, and other useful purposes. Their workshop was in Lambeth, and the date of their arrival in this country was 1673. The French were before us in the art of casting glass plates; and in 1688, Stewart commenced this branch of manufacture, which led to the establishment of the very famous works of St. Gobain. England has now large plate glass factories in different parts of the country, and these together yield as their weekly production at least 140,000 superficial feet of the best polished plate, or seven and a quarter millions of feet yearly. The value of plate glass made in England annually, including the rough kinds used for glazing roofs, &c., is estimated at 1,000,000l. France still stands very high, and her plates are extremely perfect in manufacture. St. Marie d'Oignies, in Belgium, also sends a considerable quantity of plate glass into the market. This branch of manufacture has not yet extended to America, which therefore is a large customer of Europe. Formerly, glass making was very heavily taxed in this country, and in 1812 an additional duty was placed on the manufacture of the raw material, which so greatly depressed it, that the income which the State received fell from 328,000l. to 183,000l. per annum. Moreover, large quantities of foreign glass were imported, and this too hindered the development of the industry amongst us. On the repeal of the duty, however, the trade began to increase, and has now reached very large dimensions.

Glass appears to be a mixture of silicates, the nature and chemical composition of which will be explained in a later part of this article.

The materials used are principally sand, with an alkaline substance, either a salt of soda or potash and lime, though in some kinds of glass, oxide of lead takes the place of lime. Other materials are generally employed to correct impurities which may occur in the sand, and which, if present, always impart an objectionable colour to the glass.

There are two kinds of glass in ordinary use: common window glass, which may be divided into sheet, crown, and plate; and flint glass, which is used for decanters, wine-glasses, and tumblers; and, in some special forms, for ornamental stones in imitation of jewels, and also for lenses of telescopes and microscopes. The materials for making these different kinds vary somewhat, although the principal constituents are the same, viz. sand with some salt of soda or potash.

The scientific name for sand, or more properly for its principal constituent, is silica. This compound silica, or oxide of silicon, also called silicic acid, possesses properties similar to those which belong to other acids, namely, it is able, when brought into contact with bodies of an opposite character under suitable conditions, to unite with them and to form salts. Everybody knows, that if tartaric acid be added to carbonate of soda, an effervescence takes place; carbonic acid passes off in the gaseous state, and the residue is composed of a portion of the tartaric acid, which unites with the soda, a double decomposition taking place. If silicic acid be mixed with carbonate of soda, and if the mixture be heated to a high temperature, that is, to a white heat, for some length of time, the same kind of action occurs: carbonic acid goes off, the silica or silicic acid uniting with the soda; and inasmuch as the soda salt was originally called carbonate of soda, after this action, in which carbonic acid is replaced by silicic acid, it is called silicate of soda. Silicic acid at the ordinary temperature of the air and in the dry state, has no action whatever upon carbonate of soda, but when heated sufficiently, the action becomes vigorous. A very interesting experiment may be performed in illustration of this fact in the following manner: if a mixture of carbonate of soda and carbonate of potash be heated in an ordinary fire-clay crucible, and if, when the mixture is melted, some perfectly dry sand be poured into it, effervescence will take place, owing to the expulsion of carbonic acid from the carbonate of soda and potash by means of the silicic acid. If the operation be performed in such a vessel that the carbonic acid can be collected, its presence is readily indicated by the usual tests. This experiment can be easily made by anyone who has ordinary chemical apparatus at his command. If the mixture of carbonate of potash and carbonate of soda be melted in a small platinum crucible; and if, when melted, it be removed quickly while very hot into a tall beaker-glass, and sand be then poured into it, the escaping carbonic acid will, on account of its being heavier than air, be retained in the glass, and its presence can be recognized by its turning lime-water milky (which is, in fact, a solution of lime in water), owing to the formation of carbonate of lime produced by the carbonic acid evolved uniting with the lime dissolved in the water. A mixture of carbonate of soda and carbonate of potash is here used, because either of these salts requires a very high temperature to melt it; but when the two are heated together, the fusibility of both is increased. When sand is heated with oxide of lead (common litharge) they unite, forming a compound similar to that produced by the silica uniting with the soda, as described in the last paragraph. In the first case, a soda glass is formed; in the second, a lead glass is the result. If these two glasses be mixed together and melted in a crucible, and if the proportions in which they are mixed be properly adjusted, and the materials used be pure, a colourless and transparent glass will be formed, similar in appearance to that which is employed in the manufacture of decanters and tumblers. The same kind of glass may be produced by mixing all the materials in due proportions and heating them together. If, instead of oxide of lead, lime be mixed with carbonate of soda and sand, and the mixture be heated to a high temperature, a glass will be formed, in many respects similar to that of which oxide of lead is a constituent, but differing from it in several important particulars. First of all, the lead glass is highly lustrous, and has a great power of refracting light, so that, when it is cut, it presents a brilliant appearance, and by refraction readily produces the prismatic colours. This property does not belong to the glass containing lime, to anything like the same extent. Lead glass, too, is much heavier than lime glass, and is therefore unsuited to many of the purposes for which the latter is generally used, the principal of which is for the glazing of windows.

If, instead of oxide of lead, which is a chemical compound of lead and oxygen gas, or lime, which likewise is one of the metal calcium with oxygen, carbonate of lead or of lime be used, the silicic acid will expel the carbonic acid from these substances at a high temperature, just as it does the carbonic acid from the carbonate of soda and carbonate of potash. It is necessary, for a proper understanding of the scientific part of our subject, that this fact should be borne in mind, and that the acid properties of silica should be thoroughly recognized. Formerly, carbonate of soda was used in the manufacture of ordinary window glass, but now it is found more economical to employ sulphate of soda, which is a much earlier product in the manufacture of soda from common salt than the carbonate, and is therefore less expensive. Carbonic acid is what chemists call a weak acid, by which is meant, that its compounds are not so firm and stable, as those which are formed by other acids with the same substances. Sulphuric acid is a strong and powerful acid, uniting very readily with the oxides of certain metals to form very stable compounds. But although this acid is chemically so powerful in its compounds, yet at a high temperature it is expelled by silicic acid, showing that this substance, so inert in its natural state and at the ordinary temperature of the air, becomes exceedingly active in expelling other acids and in forming compounds, when put under favourable conditions.

If a mixture of common sand and carbonate of soda, the carbonate of soda being in excess, be heated, a glass will be obtained which is slowly soluble in cold, readily soluble in hot water. To these compounds the name of silicate is given, so that we speak of the soda compound as silicate of soda, of the lead compound as silicate of lead, and the lime compound as silicate of lime. Silicate of soda and silicate of potash, when the alkali, that is to say, the soda or potash, is in excess, are both soluble. If a solution of one of these silicates be taken, and if carbonic acid be passed slowly through it, after a time a gelatinous, white, flocculent substance will be formed in the liquid, and eventually precipitated. This white flocculent substance is silicic acid combined with the elements of water, and is therefore called by chemists hydrate of silica. Now this hydrate of silica is soluble in water and in hydrochloric acid; and the method by which it can be brought into solution in water will be explained, when treating fully of what are called soluble silicates and their applications.

Soluble silicates are mentioned here, in order that a more perfect understanding of the nature of silicious compounds may be obtained, by those who do not possess a scientific knowledge of chemistry. The silicic acid in the silicate of soda is precipitated or separated out by carbonic acid, and hence it appears, that an action, exactly the reverse of that which takes place at a high temperature, occurs, when the silicic acid is removed from those conditions in which it has been seen to be (chemically) so active.

Suppose that to a solution of silicate of soda or of potash a soluble salt of calcium be added – the chloride, for example, which is a compound of the metal calcium with chlorine – a double decomposition will take place; the calcium will unite with oxygen in the silicate of soda, forming lime; and this will again unite with the silicic acid, forming silicate of lime; while the chlorine will unite with the sodium, forming chloride of sodium, or common salt.

Here then, silicate of lime is obtained by a process very different from that which has already been described, namely, by the heating of lime with silica at a high temperature. The body formed in the latter case is chemically the same as that produced in the former, there being present the same weight of calcium, the same weight of oxygen, and the same weight of silicic acid in each. Again, if to a solution of silicate of soda, one containing a soluble lead salt, such as the nitrate, be added, the silicic acid will unite with the oxide of lead in the nitrate of lead, and the acid constituent of that body will unite with the oxide of sodium or soda, forming nitrate of soda. It is apparent, therefore, from these remarks, that in whatever way the substances be made to unite, the effects produced as regards chemical composition are the same. If some of the silicate of lime or silicate of lead made by precipitation be dried and heated to a high temperature in a crucible, it will melt or fuse, and form a vitreous substance. In these last cases, as in many others which will have to be alluded to, the silicates formed are not soluble in water, although silicate of lime may be partially dissolved when heated in water under extreme pressure, by which the temperature is considerably increased, and even slightly in cold water.

To ensure the production of definite silicates by the agency of heat, the materials must be mixed together in proper combining proportions; for if more of the metallic oxide is introduced than can combine chemically with the sand, it will be melted in the mass, but the excess will not form a definite compound; whereas by precipitation, the silicates formed always have, when thoroughly washed, a definite composition. This subject will be again referred to, when the manufacture of commercial glass is described.

It has been noticed that the glass found in the windows of old churches and in other places where it has been exposed to the prolonged action of the air and of moisture, has gradually become rough on its surface, and has lost to a considerable extent its transparency. This, which would be a defect in glass for the glazing of ordinary windows, where transparency is desired, is rightly regarded as a beauty in glass which is to be used for the ornamentation of windows. Many reasons have been offered in explanation of this apparently peculiar property of ancient glass; and that which appears to be correct is, that glass is a mechanical mixture of different silicates, some of which may be soluble in water, and others insoluble. The old window glass, whose manufacture will be more fully described by-and-by, was made in a less perfect manner than modern appliances enable glass manufacturers now to produce the same article, so that the silicates composing the old glass were not as intimately mixed as those used in modern glass. By the slow action of air and moisture, portions of the soluble silicates have been dissolved out, and hence we frequently find a sort of honeycomb appearance on the surface of ancient glass, as well as a thin film, which, by refraction of light, causes an opalescence when viewed by reflected light. Efforts have of late been made to produce a similar effect by employing different methods in the process of manufacture, but without complete success. The fact, however, that such changes have taken place in this less perfectly fused glass, tends to show, that if one silicate can be dissolved out, there cannot be chemical union between all the silicates. If a piece of modern window glass be heated in water under pressure in a closed vessel, it will present somewhat the appearance of ancient glass, for a considerable quantity of soluble silicate will be dissolved out from it. The object in dwelling on this matter here, is to induce makers to attend more to the chemical composition of their glass, for, doubtless, much more satisfactory results would be obtained both as to the quality of the material and the cost of its production, if thoroughly scientific investigations were conducted by a competent chemist.

MANUFACTURE OF GLASS

The first object in glass making is to obtain suitable materials. The sand which is employed for window glass differs from that which is required for flint glass, in that the latter should be as pure as possible. The maker can correct the impurities in the window glass sand, provided they be not present in too great quantities; but it is far more difficult, in the case of flint glass, to chemically counteract the influence of those substances which might impair its tint. So that the manufacturer would rather pay large prices for his sand, than trust to expedients which in their application might fail, and thus cause a greater loss.

One of the principal and most troublesome impurities met with in sand, is iron in the form of oxide. There are two oxides of iron: one, the protoxide, which imparts a green colour to glass; and the other the peroxide, whose staining property is yellow. A very small quantity of the former will give an appreciably green tint, whereas it requires a large quantity of the peroxide to produce even a delicate yellow. In all glass making, it is found necessary to use something which will counteract the colouring properties of these two oxides. The material employed was black oxide of manganese. This is still used in certain glass-works, but from its injurious action on the fire-clay pots, arsenious acid or common white arsenic is employed to effect the same object. The chemical action in the two cases is different: the black oxide of manganese is what is termed an oxidizing agent, and gives up, at a high temperature, a portion of its oxygen to the protoxide of iron, thereby converting it into the peroxide. It thus becomes comparatively harmless, by converting a quantity of that oxide, which gives a green colour, into the other oxide, which has little or no power of colouring, except it be present in large quantities. The difficulty in using black oxide of manganese is, the exact proportioning of it to the quantity of iron present in the sand, a quantity which cannot be easily determined. If the black oxide of manganese be used in excess, some of the oxide of manganese remains unreduced, and, when this is the case, it gives a purple colour to glass. If used in exact proportions, it is reduced to an oxide which does not impart colour to glass. This may be seen in many of the old plate glass windows which were employed for glazing purposes some sixty or seventy years ago, the colour of the panes being generally purple.

Since this article was written, I have been consulted by a glass firm of eminence, as to the use of pure black oxide of manganese in the manufacture of flint glass, instead of that ordinarily supplied in commerce. The black oxide of manganese usually sold contains many other constituents besides black oxide of manganese; amongst these are iron, copper, cobalt, and alumina.

The iron, as will be seen from what has before been stated, is a decidedly objectionable ingredient to use along with the manganese.

Copper and cobalt both stain glass, the former of a bluish-green colour, while the latter makes it blue; and a small quantity of the latter has great staining power. I have thought it advisable to give analyses of the black oxides of manganese, and they are as follows:

Binoxide of manganese (Molecule, Mn.O2), is found native as pyrolusite or polyanite. Appended are two analyses of pyrolusite containing sesquioxide of iron.

The native binoxide often contains both copper and cobalt in addition to iron; frequently to the amount of as much as 1 per cent. of copper and about ·54 per cent. of cobalt.

Wad, a native binoxide of manganese, sometimes contains 54·34 per cent. of iron, while nearly all the manganese ores contain more or less alumina, varying from ·5 per cent. to as much as 20 per cent.

From the composition of ordinary commercial black oxide of manganese, as shown by these analyses, it is evident that it is better to use the pure article, and this has been found to be the case by the firm who have adopted it in lieu of commercial black oxide of manganese. I therefore strongly recommend all glass makers to try and experiment with it, for the results obtained will largely counterbalance the extra cost of the pure material; and I also much doubt whether the same injurious effects will be produced on the pots, as is the case where commercial manganese is employed.

Arsenious acid also acts as an oxidizing agent, in that it gives up its oxygen to the protoxide of iron, converting it into the peroxide; but the arsenic itself, which has lost its oxygen, is reduced to the metallic state, and being volatile, does not remain with the glass, but passes off by the flues of the furnace. If too much arsenic is used, it sometimes renders the glass milky or cloudy.

Before describing in detail the method of mixing and founding glass, it will be necessary to mention the composition of the vessels in which the glass is made. They are called glass-pots, and differ in shape according to the different kinds of glass to be made in them. Glass-pots are made of fire-clay (generally the best Stourbridge), which is a silicate of alumina, and here great care is taken to select that which contains least lime or iron. It is ground, then moistened and well kneaded together, and left to ripen, while a certain quantity of old glass-pot is ground fine and mixed with the fresh fire-clay. Masses about the size of two hands are kneaded separately, the object being to exclude all air bubbles, and to obtain a perfectly homogeneous lump. The bottom of the glass-pot is then laid, the masses of fire-clay being pressed in with the greatest care, so as to avoid all cracks or places where air might enter during the slow process of drying.

The modern shape is round; though formerly certain glass-pots, called cuvettes, used in the purifying of plate glass, were square. Pots used in the manufacture of common crown and sheet window glass, generally speaking, are larger at the top than at the bottom; but whatever may be the shape of the pot, the method of its building is the same. The sides are carefully made of fire-clay, each piece being laid on by itself and kneaded like the bottom of the pot, so that it is slowly built up until it reaches the desired height. It is then dried very gradually, and the process is finished in artificially warmed chambers. Before putting it in its place in the glass-furnace, it is allowed to remain for some time in what is called a pot-arch, that is, an archway built of fire-clay bricks, along the side of which is a fireplace, by means of which the arch is brought up to a red heat; and after it has been heated sufficiently, is removed while red-hot and put into the furnace. Glass-pots are never allowed to cool, and with care they may last for several months. From this description of their manufacture, it will be clear that it is attended with considerable cost, varying from 5l. to 10l.

There are three different kinds of ordinary pots for crown, plate, and flint glass; and of these the last is decidedly the most expensive, as its top is covered over, and presents the appearance of a dome with an opening in front, through which the materials can be introduced when the pot is charged, and from which, when made, the glass may be drawn, in order to be blown into shape by the workman. In glass-furnaces the pots are sometimes arranged in a circle, with their mouths opening into the glass-house; but now a different construction is sometimes employed, since other methods of heating the furnaces have been introduced. It is hardly within the scope of this article to enter into a description of glass-furnaces; suffice it to state, that they should be of such a construction as to yield the greatest amount of well-regulated heat for the smallest consumption of fuel, and this object seems to be best effected by the adoption of Mr. Siemens' excellent principle of heating furnaces. For some years his process has been in use at the Thames Plate Glass Company's Works, where the saving of fuel has been very considerable, and the glass greatly improved, owing to the fact that impurities from the fuel employed cannot possibly find such easy entrance into the glass-pot. In any case, the construction of the furnace is such, as to be best adapted to the convenience of the workmen, according to the kinds of glass which they have to make. Differently arranged furnaces are used for bottles from those employed for crown and sheet glass.

It has lately come to my knowledge that flint glass, that is to say, the glass used for tumblers, decanters, and such like, is occasionally injured by the appearance in it of little opaque white spots. Some portions of glass of this character have been analyzed by me, when I found that these white spots were owing to the presence of a glass containing alumina. Now alumina raises the melting point of any glass of which it is a constituent. So, then, these white spots were due to the presence in the flint glass, which was perfectly clear, of a much less fusible glass which was only partly made when the flint glass was ready for working. On investigating the matter, it was found that the alumina came from the glass-pots, for when by my advice the faulty pot was withdrawn from the furnace and carefully examined, although it had been in work only six weeks, the bottom was honey-combed to a very considerable extent, showing that portions of the pot had been dissolved; and inasmuch as the fire-clay, of which the pots are made, contains a large quantity of alumina, it was not difficult to trace the source of these white spots which had rendered useless much very valuable glass. On inquiry it was found that the pots had been made entirely of new clay, and on reference to the book of workings, which was kept in the glass-house, it was also found that for some time, the glass-pots used in that establishment had been made of new clay, and that on a previous occasion a similar calamity had before happened.

In the records kept where pots were made, as has already been described, with a portion of old pot as well as new clay, no white spots had ever appeared in the glass. It is therefore manifest, that it is much safer to use a portion of old pot than to trust to pots made entirely of new clay.

Having considered briefly the manufacture of glass-pots, I shall proceed to the treatment of the materials to be employed. In making common window glass, ordinary sand, which does not contain any very large quantity of iron, may be used, the alkali employed being sulphate of soda, while the purifying material is either arsenic or black oxide of manganese. A small quantity of anthracite coal is added to the mixture, in order to assist in the reduction of the sulphate of soda, together with some lime. The materials are carefully mixed and placed in the furnace, where they are heated for some time, a process which is called "fritting." Its object is to perfectly dry the materials, so as to expel carbonic acid gas, which would otherwise cause swelling in the glass; but no combination must take place, to allow of silicates being formed, otherwise the alkali would melt first and attack the substance of the glass-pots, and part of it would be volatilized and lost. When this operation is completed, the fritt is put into the hot glass-pot, and submitted to the action of the heat of the furnace, until the glass is made, or "founded," as it is technically termed. In the case of sheet and crown glass, this process lasts from sixteen to seventeen hours, for it will be remembered that the top of the pot is open to the furnace, so that the flames pass over the surface of its contents. In this way the materials get heated more rapidly than when a covered glass-pot is used.

M. Gehlen gives as a good mixture for window glass:

Different makers have different mixtures. This by M. Gehlen is given as about the proportions of the several constituents employed.

The charging of the pots is conducted in this manner: they are filled with lumps of fritt, and the heat of the furnace is raised as rapidly as possible, until, in about eight or nine hours the fritt has run down or melted into glass. More fritt is then added, which also melts, and from time to time this is repeated, till the pot contains a sufficient quantity. After about sixteen hours the whole has become converted into glass, and the surface of the molten mass is covered with liquid salt and sulphate of soda. This scum is called glass-gall or sandiver, and is carefully removed with iron ladles. Some broken glass, or cullet, is now thrown into the glass-pot, a little at a time, the object being to cause any salt which may remain in the pot to rise to the surface, which is then removed, and so the glass is in this manner purified, after it has been further heated for some hours, to expel gases.

When the glass is made, and its temperature so reduced that it is in a doughy or pasty state, it is then worked off by the blowers into either sheets or tables, as is desired. The blowing of sheet and crown glass is a work of considerable difficulty and labour, and one which cannot be successfully performed, except by a workman who has been brought up from boyhood in a glass-house. A quantity of the soft glass is collected or gathered on the end of a blowpipe, and the workman then blows into it, and distends it into a globular form. Now it is necessary, in making sheet glass, that that globular form should be elongated; the workman therefore holds his blowpipe, which is about five feet long, in a vertical direction, and the softened globe becomes pear-shaped. By dexterously swinging the blowpipe from side to side, which he does while standing on a plank placed over a sort of pit, and by causing it to rise on either side, he converts the pear-shape into a true cylinder, having rounded ends. When the cylinder has assumed the exact shape desired, he places his thumb on the end of the blowpipe, and holds the opposite end of the cylinder in the mouth of the furnace. The glass softens at the heated end, and the expanding air causes it to burst the opening. It is then shaped with a suitable tool, so that it is of the diameter of the cylinder. When the latter is cooled, a piece of hot glass is applied to its shoulder with a pontee, and is drawn out into a thread around it. This makes the glass hot. The thread of glass is removed, a cold instrument is applied rapidly, and the shoulder of the blowing is cut off. The glass is next detached from the blowpipe, and its ends removed, and it is then annealed for a short time, and cut down lengthways internally by a diamond. It is afterwards placed, with the long cut uppermost, in what is called a flattening kiln, that is, in a sort of oven or furnace heated to a high temperature and having a perfectly smooth stone floor; after a short exposure the glass softens, and a workman, with suitable wooden tools, opens it out where it was cut by the diamond, and causes it to lie flat upon the stone. It is then rubbed by a wooden tool, and in this way is flattened, removed from the flattening stone kiln, and placed in a hot chamber, in which it is allowed to cool slowly, for the purpose of "annealing."

The soluble silicates are frequently used as bonding materials in the manufacture of artificial stone and cement, very good results having been attained. The objection, however, to their employment for these purposes is the expense of the material of which they form a constituent part, and it seems almost impossible ever to bring it into competition with dressed natural stone. But for ornamental purposes, from the plastic nature of the substance when in the wet state, it can be pressed into moulds, and wherever plaster mouldings are admissible, no doubt this material would be useful for certain kinds of ornamentation. Some years ago, Mr. Ransome, of Ipswich, after having made his artificial stone with sand and silicate of soda, heated it in ovens, so as to produce a hard and semi-vitrified mass. A church, the mouldings of which are made of this stone, may be seen at the bottom of Pentonville Hill, London; and certainly as to durability, there is no doubt that the substance has answered very well. But from difficulties in manipulation and other reasons, that gentleman gave up this method of making artificial stone, and is now working another process which yields far better results. Silicate of soda is mixed with sand (generally Aylesford sand), and after the mixture is moulded and dried, it is exposed to the action in vacuo of chloride of calcium in solution. Whether the whole mass is placed in a vacuum chamber and then charged with chloride of calcium; or whether a vacuum is formed on the under side of the substance, and the chloride of calcium solution caused by suction to filter through it, is uncertain. However, whatever be the manipulative processes, the result is the same, and appears to be extremely satisfactory.

Soluble silicates produce very remarkable results when mixed with certain substances. If silicate of soda or potash be mixed with white lead, in a very short time it sets into a hard substance, just as does plaster of Paris when mixed with water. If powdered pumice-stone or sand, in the proportion of eight parts to one of carbonate of lead, be mixed together with soluble silicate, a very hard and coherent mass is obtained, and there seems no reason why a mixture of this kind, in which pumice-stone is used, should not be employed for the purpose to which pumice-stone is usually applied. It would have the advantage of being easily moulded into forms, so as to suit mouldings, which might by it be much more accurately and expeditiously smoothed down (as in the case especially of picture-frame mouldings), than they can be by the ordinary pumice-stone.

Another very important application of soluble silicates is the rendering of wood incombustible. Many experiments have been performed which show that when wood is thoroughly impregnated to a depth of a quarter of an inch or more with silicate of soda, it will not flame, but will only char. Now, supposing that the constructive timbers of a house were worked, and then placed in suitable vessels and saturated with silicate of soda, they would then be rendered practically fireproof, or at least it would take a very prolonged exposure to heat to cause them to smoulder away, while at no period of this time would they burst into flame. From the peculiarly gluey nature of these soluble silicates, they do not penetrate readily into porous substances; it has therefore been suggested that the impregnation of the wood should take place in vacuum chambers, just in the manner that the creosoting process for preserving railway sleepers is at present performed. It is most certainly advisable that the wood should be worked before being exposed to the silicating process, for that would render it so hard, that it would considerably increase the cost of labour in cutting and planing it.

At the commencement of this article, it was stated that silicic acid, or silica, could be made soluble in water. Some very interesting experiments were performed by the late Dr. Graham, Master of the Mint, which gave rise to the discovery of the process of dialysis. If some silicate of soda be mixed with water, so that not more than 5 per cent. of silica be in the solution (rather less is better), and if some hydrochloric acid be then added in sufficient quantity to make the liquid distinctly acid, and the mixture be placed in a dialyzing apparatus, the chloride of sodium formed by the union of the chlorine of the hydrochloric acid with the sodium of the silicate of soda will pass out through this dialyzing membrane, leaving hydrated silica behind, which will remain in solution in the water with which the silicate was mixed. The dialyzing apparatus is constructed in the following manner; a sort of tambourine ring is made with gutta percha, in place of wood, from 8 to 10 inches or even more in diameter, the depth, being about 2 inches. Another ring of gutta percha, of about an inch deep or even less, is made so as to fit tightly outside the tambourine; a piece of vegetable parchment is then moistened and placed over the tambourine, and the thinner ring is pressed over it, so as to secure it tightly. This is the dialyzing vessel, and it is into this that the mixture of silicate and hydrochloric acid must be put. The solution should not be more than an inch deep in the dialyzing vessel, which is then made to float upon distilled water in a larger vessel of suitable size. The distilled water should be changed every day, until no precipitate can be obtained in it with nitrate of silver, and when this point is arrived at, all the chloride of sodium will have passed through the vegetable parchment into the larger vessel of water, and nothing but silicic hydrate will remain behind in solution. If this liquid be allowed to stand for some time, it will gelatinize, and later on the jelly will contract, becoming extremely hard, so that lumps of it, when broken, will in their fracture resemble that of flint. No doubt, at some future period, some one will discover a method of rendering this condition of silica useful in the arts.

Soluble silicates are very useful as detergents. A small quantity of silicate of soda mixed with hard water renders it valuable for washing purposes. Silicate of soda is also used in the manufacture of the cheaper kinds of soap. We can hardly speak of it as an adulteration, because it renders the soap with which it is combined much more powerful in its cleansing action. I suggest to those interested in the application of science to the arts, that this subject will no doubt well repay experimental investigations.

It is much to be wished that those engaged in this branch of art and manufacture, and who have some knowledge of chemistry, would turn their attention to getting a better and more perfect method of making coloured pot-metal glass. I have been engaged for some time, and still am engaged, in experiments to effect this object. But inasmuch as my engagements are very numerous, and I cannot give the proper time to it I desire, I therefore take the liberty of suggesting to others the ways in which I am working, that they may be able to arrive at good results more speedily probably than I shall be able to do. If sulphate of copper be mixed with silicate of potash, silicate of copper will be precipitated. Now, if this be carefully washed and dried, it will be a silicate of a definite composition, and I propose to use such silicates as these with ordinary glass mixtures, in order to impart the particular colour which the oxide employed has been already described as giving to the glass. Silicate of manganese is prepared in a similar way to the silicate of copper; silicate of cobalt, and other silicates, can be used as staining materials for colouring glass. These mixed in due proportion would give tints, and would, I do not feel the slightest doubt, produce colours with much greater certainty than they are now produced, and tints hitherto unknown could be made to the great benefit of the glass-painter.

FURNITURE AND WOODWORK

By J. H. Pollen, M.A., South Kensington Museum

I propose in the following pages to give some account of the materials used in making furniture, and of the arts applied to its decoration. From the earliest ages of society, when men moved about in tribes, they had in their tents of camels' hair simple necessaries, such as their wants required. Before people were gathered into distinct nations, or cities built with walls and gates, there were still certain human wants that must needs be supplied; and the objects that were needed to enable mankind to live with convenience and decency were found in their furniture. To this very day we may see Arab tribes wandering over sunny deserts, seeking pasturage, sowing here and there an acre of wheat or barley, or gathering dates. Their camels and dromedaries are their waggons, their horses are their friends, their families and those of others that make up their tribe are their only nationality. Yet they furnish in some sort the temporary homes which they shift from one spring of water to another, as the patches of grass or grain grow up and ripen. Their chief wants are, a cloth strained over three staves to make a house, mats or carpets to lie on, a few bowls to cook in, saddles of wood, and a few baskets or chests, made of light sticks fastened together.

In later periods of history and in more conventional states of society, we shall find this primitive type of furnishing carried out with growing splendour. In the West and in the East, in ancient and mediæval times, great rulers, though constantly in the saddle, have been followed by enormous trains of camp followers, by whom costly furniture, hangings, vessels of plate, and other luxuries, have been carried for the convenience of the leaders and warriors of moving hosts; and of course this splendour was the measure of the state and magnificence kept at home. The wealth or feudal state, shown in the furniture of old castles and palaces, extended not only to halls and rooms, but to dresses, and armour, weapons, the furniture of horses, tents, and other objects that could be carried on distant expeditions.

Ancient nations have been as well, and more splendidly, if less conveniently, provided with furniture for their houses than modern ones. It happens that there are distinct records of many kinds, showing what wealth and elaborate decoration some of the oldest races, such as the Assyrians, the Egyptians, the Persians, and the Greeks, bestowed on their thrones, beds, chairs, and chariots. Beds of silver and gold are mentioned in Esther i., and the curtains of the bed of Holofernes were covered with a canopy of purple and gold, with emeralds and precious stones (Judith x. 19; Esther i.). Modern princes in India continue to devote their jewels and gold to similar uses. It must be borne in mind also, that this kind of splendour is an investment of property in times and countries in which banks, insurance offices, government funds, and other organized means of investing money are unknown.

Silver, if not gold, has been used occasionally, not only in the East, but in Europe, for seats, tables, even the frames of pictures and mirrors. The royal apartments in Whitehall were completely mounted with hammered and filagree silver furniture in the seventeenth century. Carlyle records of Frederick the Great, that silver ornaments were kept in his palace, and turned to account under the exigencies of war. But of furniture generally, wood is the readiest and most proper material. It is handy, easily worked, light to carry about, and may be manufactured with or without decorations of carved work, or of any other kind. Hence, in giving an account, whether historical or mechanical, of furniture, I class it under the more general head of woodwork. Any other materials, either for the framing or ornamentation of furniture, are exceptional. The remarks now to be submitted to the reader will refer to wood that is manufactured, though I shall not enter on the interesting subject of wood structure, which has been applied to such noble and elaborate uses, and of which such splendid monuments of many periods still remain for us to study.

Most of the methods used for decorating woodwork made up into furniture are still in regular use, and the processes of putting it together are the same as they have always been. The reader may satisfy himself on this point any day by a walk in the Egyptian rooms and in the Nineveh galleries of the British Museum. In both these sections of that wonderful collection, there are remains of woodwork and of furniture, made of wood three or four thousand years old, such as stools, chairs, tables, head-rests or pillows, workmen's benches of Egyptian manufacture, fragments less complete of Nineveh make that have been portions of various utensils, and precious articles of sculptured and inlaid ivory that have been inserted into thrones and chariots. These pieces of furniture have been mortised together, or joined by dowels, dovetailed at the angles, glued, nailed, or, in short, made up by the use of several of these methods of junction at the same time. And no great changes have been introduced in the various ways of ornamenting furniture. The Egyptian woodwork was painted in tempera, and carefully varnished with resinous gums. It was inlaid with ebony and other woods, carved, gilt and, perhaps, sparingly decorated with metal ornaments. The Greeks inlaid chests and tables with carved ivory and gold, sometimes relieved with colour. The Romans, who made much furniture of bronze, cast, inlaid, damascened and gilt, made much more in wood, which they stained, polished, carved, and inlaid. Mediæval furniture was put together with mortises, tenons and glue, and was gilt and painted; the painting and gilding being laid on a ground prepared with the utmost care, and tooled and ornamented in the same way that bookbinders ornament leather. At a later period, a beautiful manufacture was carried on in various parts of Italy; a sort of mosaic in very hard stone, such as agate, lapis lazuli, and other precious materials. The Italians also used these beautiful stones inlaid in ebony. But the furniture most valued in modern times has been that which owes its name to Boulle, a French artist of the seventeenth century; and the marquetry, or wood mosaic surface decoration, which reached so high a standard of excellence during the last thirty years of the eighteenth century in France.

The former of these two classes of manufacture made, if not originated, by Boulle (and I am inclined to think that he was not the first maker), was a marquetry, or surface decoration, not composed of various woods, but of tortoiseshell and brass, with the occasional introduction of other metal, and with metal enamelled in blue and other colours. The materials principally in use, however, in Boulle marquetry are tortoiseshell and brass. In the older work, viz. that of the seventeenth century, the tortoiseshell is dark, and left in its natural hue. In later Boulle, called new Boulle, the tortoiseshell is reddened by colour, or by gilding laid under it. There is much grace and variety in the delicate arabesque designs in which one material is inlaid in the other. Parts of the surfaces are sometimes diapered, as a contrast to the free lines and curves of other parts. The inlaid surface of Boulle work is framed in by borders, cornices, or handles of brass or gilt bronze, giving a massive architectural character to the whole.

Thus if we look back to the history of furniture, not only will every kind of splendid material be found devoted to the manufacture or decoration of it, but the best art too of many different periods that money could command. It is in the late times of antiquity, and since the period of the Renaissance in modern times, that works of art have been kept on shelves or gathered into galleries. Many works of great masters, such as the chest of Cypselus, and the chairs of the great statues of ivory and gold, were prepared for celebrated shrines and temples in the cities of Greece. It was but the excessive wealth of great patricians in Rome and Constantinople that led to their becoming collectors, whether of sculpture, painting, or sumptuous silver plate. The chief object of rich and accomplished men in most ages of luxury and refinement has been, to make the house, its walls, ceilings, floors, and necessary or useful furniture, costly and beautiful. It was the same in the days of Donatello, Raphael, Cellini, and Holbein. Chests and trays were painted, together with gems, dies, brooches; table plate was modelled and chiselled; while chairs of wrought steel, or tables, cabinets, and other pieces of rich furniture, were either designed or carried into execution by these masters with their pupils and followers. In some instances, as, e.g., in that of the famous Pomeranian cabinet, in the Kunst Kammer in Berlin, a long list has been preserved of artists and craftsmen of note in their day, who combined to produce monumental examples of actual room furniture.

It cannot be denied that though great pains are taken and much expense is incurred in modern furnishing, the habits of the day lead rather to the search for comfort than for grace or beauty; and convenience rather than intrinsic value or artistic excellence. Nevertheless, a certain amount of decency and splendour is indispensable in both receiving and sleeping rooms; and though a house really well, that is beautifully, furnished is of rare occurrence, this is not for want of serious efforts, nor altogether to be laid to the account of unwillingness to spend money for such a purpose. Whether the "art of furnishing" or the desire to have what people require for use in their houses more becoming and beautiful, be a rising influence or not, it is certain that the "fancy" or ornamental furniture trade is of large and increasing importance, corresponding to the increased size and cost of modern London and country houses, compared with those built during the reigns of William III. and George IV. Every tradesman who has the pretension to repair chimney-pots, to whitewash, or paint house-fronts, ceilings, or offices, writes up the word "decorator," on his shop-front.

The Qualities required in Furniture

We may consider furniture under two broad divisions, that which is made to be handled and moved about, and that which is for use but not meant to be handled or moved. We may add a third division in the actual fixtures of the house, made by the joiner and meant to be ornamental fittings or completions to the builder's and carpenter's work.

Under the first head will be included light tables, chairs, couches, and other movable objects; under the second, cabinets, book-shelves, frames, mirrors, and so on; under the third head come flooring, panelling, window shutters, door-frames, stair-rails, &c.

1. Chairs, Tables, etc

The essential points in a well-made chair are comfort, lightness, and strength. Of course, as men and women are pretty much of the same proportion all over the world, chairs, of which the seat is about the height of the lower process of the human knee-joints, must be of the same height, or but slightly varied, in every country. From the habit that so many persons have of throwing their whole weight back and, as we are told, in some countries, of balancing their persons on the back legs of their chairs and inclining their legs in the direction of the chimneypiece, there is often an immense strain on the back joints of chairs. Whether we lean back or swing on them, the junction of the seats of chairs with the backs is always subject to severe trials; and on no article of furniture in common use is such good joinery required. It is worth while to look at the old wall paintings of the Egyptians, as they are given in Rossellini and the great French book of the 'Description de l'Egypte,' to see what capital workmanship those most ancient carpenters bestowed on their chairs. Those of the best and oldest periods are without connecting bars to the legs before or behind, all the strength of the construction being centred in the excellence of the joints of the seat with the back and legs; and in modern workshops, the highest skill is applied to ensure strength in these points of junction. If the wood is thoroughly dry, the mortises and tenons fitting perfectly, and the glue good, the different parts are so wedded together that the whole structure becomes one piece, as if nature had made a vegetable growth in that fashion, all the fibres of which have continuous and perfect contact with each other. If, however, there is a deficiency in any of these conditions, these joints fail. If the wood shrinks, or the tenons do not fit the mortises all through, or the glue is deficient, these various portions speedily come to pieces. Sofas, couches, and stuffed chairs are so much more massive in construction that there need be no risk of such a kind of disintegration.

The members of which a chair is made up may be either turned in the lathe, or left massive enough to allow of carving on the legs, backs, or round the framework of the seat. Turned work can be lightly inlaid with ivory, as that of ancient Egypt, painted, gilt, or mounted (lightly also) with metal.

The subjects of the carving may be either figures of men, horses, lions, or the heads and legs of such animals, acanthus leaves, and arabesques. Many of these ornaments have been used from ancient times, and revived at various historical periods. For modern rooms the lightest construction is most in place, and therefore carving should be compact in composition and delicate in execution, without prominences or undercutting that would interfere with comfort or be liable to breakage.

A certain architectural character is given to chairs by cutting flutings down the legs, or by borrowing other slight details from architecture. The upholstery of chairs will always be their most noticeable decoration, and this applies still more to lounging chairs and couches of all shapes and sizes, as the framework of them is so much less observable in proportion to their upholstered surfaces.

Tables, lampstands, &c., being generally, though not always, meant to be moved about, require as light a construction as is consistent with strength. The surface of all but small tables is beyond the dimensions of a single plank of wood. The outer and inner portions of a log or plank are of different fineness of grain, contain varying proportions of sap, and shrink in different degrees. Single planks of wood, therefore, can only be exceptionally used for table tops. Generally, they are made up of portions of planks selected with great care, grooved on the edges, with a tongue or slice of wood cut the cross way of the grain, uniting the planks about the middle of their thickness; the edges are then firmly glued together. If the surface is to be of wood which can be procured in large pieces of straight or continuous grain, such as mahogany, the wood is solid throughout; if of some rare wood or rare figured graining, such as the roots or wens of oak, this ornamental surface is laid on in thin slices with glue and heavy pressure. This is known as veneering. The surface is sometimes inlaid with ivory, metal, mother-of-pearl, slices of agate and other substances, as in the Boulle or marquetry work already alluded to.

The frame of the table is either a deep rail not far within the edge, or a thick pillar or leg or several legs collected, mortised into a broad expanding foot and supporting a spreading framework above, to which the top itself can be fastened, and stretching far enough all round in the direction of the edges to give a firm support.

The decoration of the top can only be superficial if the table is for use, and any decoration by carving, piercing, and so on, must be confined to the framework and the supports. These parts can be, and have been at all times decorated as the framework of chairs, and by very much the same kinds of ornament.

To tables of more modern periods, little galleries of pierced work or of tiny balustrades are sometimes added. They belong to the age of porcelain collectors, hoops, broad coat-skirts, and tea-parties, and are intended to save delicate wares from being swept to the ground. Side tables, and such as are made to support heavy objects, can be treated with more massive frame work and supports, and the carving and decorations will be bolder and larger accordingly.

2. Cabinets, etc

I will proceed to the second division of furniture, cabinets, bookcases, and other standing objects, which are more or less immovable. But shelves and china trays must be placed in secure parts of the room, if they are not actually fastened to the wall. The former must be strong to support the great weights laid upon them, and the supports or framework, which is all that would be seen, may be carved or decorated with surface or applied metal ornament. On a large scale, fittings of this kind belong rather to architectural woodwork. China holders, whether placed on the ground or fixed against a wall, are properly treated with shelves quaintly shaped on plain and light, pierced galleries or gilt decorations corresponding with the apparent lightness of pieces of porcelain. The wood and lac work cabinets of the Chinese; and the complicated, but not ungraceful, gilt mirror frames and flourishing acanthus work of the Italians, French, and Germans, of the last century, seem specially suited for showing off this gay and fragile material. The collector proper will probably place his treasures under glass, and with little regard to the framework of his cases. Here china and china stands are treated only as decorations.

As to cabinets, they are the most precious, if not the most useful of all pieces of furniture. They have generally been intended to hold family treasures, are not required to be moved, and have therefore been the richest and most decorated objects in the room. Cabinets are the legitimate descendants of the chests of former days containing bridal outfits and trinkets, or plate, jewellery, and other valuables. They were carried from town to country, from grange to castle. About the beginning of the sixteenth century, the personal habits of great men became less nomad, and their chests were no longer liable to be packed and moved away. These receptacles were mounted on stands at which height the lids could not be lifted, and doors were substituted. Drawers took the place of shelves or compartments, and every sort of ingenuity was applied to make these pieces of furniture quaint and splendid inside and out.

As to shape, it is contrary to their purpose of convenience and interior capacity, to make cabinets, cupboards, or other receptacles, with showy and spreading architectural details, such as cornices, architraves, columns, pediments, and the like. All these parts, which are laborious and costly in construction, are so many additions to its size, and make no more room inside to compensate for this expenditure. Cabinets should, in propriety, be as big and convenient inside as their size would lead us to expect.

On the other hand, the many fine examples made in the sixteenth and seventeenth centuries in this country, Holland, Germany, France or elsewhere, have been generally intended for rooms larger, higher, and with fewer pieces of furniture in them than those of our modern houses, not to speak of the massiveness of fireplaces and fittings with which they were in character. It is their age, and the connection, which we cannot help tracing, with old houses and bygone generations which give architectural cabinets an interest now.

In construction, the skill of the cabinet maker will be shown in the neat and convenient arrangement of drawers of various depths and sizes, shelves or repositories, so contrived as to turn the entire internal space to account. The most curious contrivances are often found in old German, English, and French cabinets, bureaux, secrétaires, and other varieties of this kind of furniture. Pediments, capitals of columns, and other parts of architectural fronts are made to open, and secret drawers stowed away with an ingenuity almost humorous. It is upon the fronts and stands that the skill of great masters of the craft has been bestowed. The large wardrobes, or "armoires," of Boulle are examples of great inventive and designing power, as well as the marquetry of Riesener and David, and the chiselled metal-work of Berain, Gouthière, and that of many English artists.

As in past times, and so in our own, it is on cabinets that the real triumphs of the cabinet maker's art are displayed.

3. Fixed Woodwork

Thirdly, the joiner's and cabinet maker's art plays an important part in the fixed furniture of the house, and the woodwork, such as flooring, doors and door-frames, panelling, chimneypieces, with the complementary decorations of hangings, whether tapestry, silk, or the more humble material of paper.

In this last division of furniture the work is that of joinery. There is no great demand for constructive strength, as the work is fixed to walls; but as doors and shutters are swung to and fro continually, and subject to jars and strains, their stiles and rails, upright and cross-framing members, as well as the panelling that fills them, require well-seasoned timber and the most accurate workmanship: without these conditions the joints open, the panels shrink from the grooves in which the edges are held, and split, while the frame itself, if of unseasoned material, 'buckles' or twists, so that the door or shutter will no longer shut flat in its frame.

Panelling and fireplaces are, however, opportunities for the display of carving, inlaying, and gilding. The reader has seen carved room panelling, probably, in many old houses. In some of the municipal 'palaces' in Flanders, e.g. in Bruges, and in the old rooms of the Louvre in Paris, carved panelling of the utmost grace and perfection, some of it in groups of life-sized portrait figures, may be studied by the tourist.