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The photographic news
- Bandzählung
- 27.1883
- Erscheinungsdatum
- 1883
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- Englisch
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1276, February 16, 1883
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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and natare placed at his hand the food, the fuel, ami the clay from which to fashion his vessel. A visit to any museum of antiquities (say the British Museum) will generally reveal the modes of cooking adopted by the ancients. We shall find there vessels of undoubted antiquity, which have evidently been submitted to fire for the purpose either of cooking, or of some process of manufacturing ; and from this it is quite evident that the most remote of ancient races had discovered the properties of the refractory aluminous earths which we now call fire clay. Fire-clay is, generally speaking, a combination of alumina and silica, with traces of chalk, iron, magnesia, &c.; the nearer it approaches to pure alumina without the silica, chalk, &c., the more refractory it is: in other words, these impurities destroy its power of resisting high temperatures. It is a singular matter of remark, that re fractory clays are to be found all over the world, frequently in close proximity to fusible clays, and that fortunes have been made by the discovery of enormous deposits of fire clay, especially when they happen to be of excellent quality, or situated close to seats of manufacturing industry. Seeing that in the manufacture of all goods requiring in tense heat fire-clay must play a most important part, it is no.wonder that great attention has been given to the fabri cation of refractory materials, as fire-bricks, slabs, tiles, crucibles, melting pots, small furnaces for laboratory work, and even gas-burners. In England, we have vast deposits of fire-clay, named, in the order of their merit, Stafford shire, South Wales, Devonshire, Shropshire, Cornwall, and the Isle of Wight. On the continent of Europe, fire-clay of excellent quality is found in France, Belgium, Germany, &c.; none, however, surpass our own Stourbridge clay in those qualities which make it especially valuable for the formation of refractory vessels and bricks. At almost any oil shop in London one may purchase a single pound of fire-clay at the cost of (say) one penny. It will generally be found to be a leaden-coloured, coarse powder, dry and crumbly, scarcely soiling the hands, and with a faint earthy odour when presented to the nose. If we take a basin or a mortar, and place therein the contents of a paper packet of fire-clay, just as it comes from the oil shop, and add thereto a small quantity of water, we shall find that, with the assistance of the pestle, we can knead it up into a stiff, doughy mass, and if we do not “drown the miller,” we can remove the ball from the mortar, roll it about in the hands, and fashion it just like so much putty. Hero we see the difference between fire-clay and common brick earth, such as the London clay, so plentiful in the gardens of suburban villas. If common brick clay be once dried, it parts with its property of being worked up again into a plastic state ; whilst fire-clay may be dried, ground up to powder, wetted and moulded, dried, ground up, and wetted again, and the process repeated several times until it shows signs of losing its extraordinary property of plasticity. Many years ago, in our experi ments in making little furnaces and articles employed in the melting and casting of metals, we recollect our delight at the discovery of this remarkable property of fire-clay; but we discovered something else, for, having obtained posses sion of a slightly-damagedoil-drum, about two feet in height by one foot in diameter, we commenced to convert it into a furnace by lining it inside with stiff fire-clay, and made a beautiful job of the inside, a place being left at the bottom for the grid, and an outlet at the back for the draught. Picture our horror, a week afterwards, to find that our beautiful lining, in the process of drying, had shrunk and cracked, and left the sides of the furnace, and was, in fact, all in pieces. This is the effect of shrinkage, which all clays are liable to—some more than others. If we had had the knowledge that the shrinkage could be almost entirely prevented by mixing with the new clay a quantity of broken-up bricks, or old crucibles smashed into a coarse powder, and intimately kneaded into the mass, our furnace would have retained its form and size when it became dry. Now this is exactly what has to be done with nearly all fire-clays, either for making bricks for furnaces, or for pots or crucibles for melting, because the shrinkage that would occur by the use of raw clay would cause the articles to crack and be unsound and irregular in form, and lead to endless confusion, loss, and disasters. We cannot afford the space to describe in detail the fabrication of pots; if we did so it would occupy some fifty pages of the News, and might lead photographers to imagine that we had forgotten our name and aim ; but whilst we hold ourselves out to the world as a technical organ of photographic art, we deem it to the advantage of our readers to educate them a little in the kindred sciences, and this is our only apology, if apology be neces sary. Let us tiy to describe the manufacture of a glass pot in stilted language. Given—A, Stourbridge clay, ground; B, the same which has been burnt; C, ground up old pots. Take of these— A. Ground fire clay ... ... 7 parts B. Burnt fire clay ... ... ... 5 „ C. Ground up old pots 5 „ Mix with water, and form a stiff dough. A and B are generally mixed first with water, and kneaded by foot. When thoroughly incorporated, the mass is divided into handy lumps. The crucible maker then begins operations. Ona stone or iron plate sand is sprinkled ; then commences the formation of the bottom of the pot, by the pressing together of the lumps of clay, j ust like uniting so many rolls of butter ; then he begins to form the walls, the sur face of each layer being scratched to hold the next, and so on the process is repeated layer by layer until the pot is complete. Several pots are built during the same period, the pot maker working first on one and then on another; if he leaves one, he covers it up with a damp blanket. It is no uncommon thing to see in the pot-lofts from fifty to one hundred pots ready for use, or nearly so, as many months have to elapse from the time a pot is started until it is ready for the fire. A capital of £1,000 can easily be sunk in pots. A good pot maker is a valu able servant; good pots are a manufacturer’s sheet anchor ; bad pots may be his ruin. The legitimate life of a pot ends by its gradual wearing away in the furnace ; the alkalies and the fire eat into its walls, and render it ultimately so thin as to be incapable of withstanding the pressure of (say) a ton of molten glass. On the other hand, a bad pot may burst at the first fusion, and set a ton of molten glass swimming down through the bars into the “ cave,” and generally play such havoc as one could scarcely picture to the imagination. Cases have been known where, in an eight-pot furnace, no less than twenty-one pots have had to be “ set” during a single month ! Such accidents must sooner or later ruin the manufacturer. A good pot should stand at least forty fusions, and may run even to six or as long as twelve months ; much depends upon the class of work, the nature of the mixture, the quality of fuel, and skill of the workman. Fig. I. As many months must elapse between the commence ment of a pot and its fiery ordeal, it follows that the anxiety of a manufacturer must always be great, because
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