  There are plenty of receipts for the composition of flint or crystal glass, but no mixture that we know can secure a uniform shade in each pot. The component parts of glass are well known, and the mixer's sure guide is to watch the effect of heat on each pot, for he soon finds the mixture that gives good color in one pot will in another in the same furnace prove bad. If he possesses sufficient knowledge of the chemical causes, he can correct the evil. Among the valuable receipts for rich colors is the following, for RUBY GLASS, which takes lead both in cost and richness:— Take one ounce of pure gold; dissolve in a glass vessel two ounces pure sal ammoniac acid, and five ounces of pure nitric acid, which will take six to seven days; drop in at a time say one twentieth part of the gold. When the first piece is dissolved, drop in another twentieth portion of the gold, and so on until the ounce of gold is all dissolved. This will require twenty-four hours. Evaporate the solution to dryness. Then prepare in a glass vessel six ounces pure nitric acid, two ounces muriatic acid, and one ounce of highest proof alcohol; mix them well together, and drop in pure grained tin a bit at a time, but beware of the fumes. Stir it well with a glass rod; dilute the solution with eighty times its bulk of distilled water; then take the prepared gold, dissolved in a quart of distilled water, and pour it steadily into the solution of tin as above prepared, stirring all the while. Let it settle twenty-four to thirty hours; pour off the water, leave the settlings, pour in two thirds of a quart of water. Stir it thoroughly; let it settle thirty hours; pour off as before, and filter the precipitate through filtering paper. The result is the purple of Crassus. The ounce of gold thus prepared must be well incorporated with the following batch: say thirty-two pounds fine silex, thirty-six pounds oxide of lead, sixteen pounds refined nitre; melt the same in a clean pot, one little used, and smooth inside; when filled in, put the stopper to the pot loose, leaving it slightly open; leave it five or six hours, or time to settle, then a back stopper can be put up. In the usual time it will be ready to be worked out in solid, egg-shaped balls, and exposed to the air to be partially cooled; they are then to be placed in the leer under a strong fire, which will in two or three hours turn them to a red color; then the pans may be drawn slowly to anneal the balls. It is well known to mixers that colored glass is derived from metallic oxides. To obtain the proper color depends on the purity and strength of the metallic oxides. The following receipts have with success been used:— ALABASTER.
BLACK.
CANARY.
The common colors of purple, blue, emerald, or green, are too well known to require to be repeated here. The following receipt for crystal glass is on the European standard, viz.:—
GERMAN SHEET GLASS.
Gold-colored spangles may be diffused through the glass by mixing gold-colored talcs in the batch. AGATE.
BLACK.
LIGHT EMERALD GREEN.
ORIENTAL GREEN.
OPAL.
Said to turn without cooling. William Gillender, of England, gives the following receipt for Bohemian Red, or Ruby:—
Add one ounce of purple of Crassus to every eighty pounds of the above batch. WAX RED.
This he says is very good. TURQUOISE.
VIOLET.
Receipts for window-glass are as numerous as for flint. The following are in general use in England, so says Gillender:— CROWN GLASS.
PLATE GLASS.
DIAMOND GLASS. Four pounds of borax, one pound of fine sand; reduce both to a subtile powder, and melt them together in a closed crucible set in an air furnace, under a strong fire, till fusion is perfect. Let it cool in the crucible, and a pure, hard glass, capable of cutting common glass like a diamond, which it rivals in brilliancy, is produced. LEAD.Lead is an important and costly ingredient of flint-glass, used as a protoxide, either as litharge or red lead, and should be perfectly pure, for the presence of any other substance or metal will be shown in the color of the glass. Consequently, the purity of the glass depends mainly on the quality of the metallic lead and its being well manufactured. The writer believes he was the first person in the United States, aided by a director of the New England Glass Company, to build a lead furnace. This was in 1818. His only guide was a volume of "Cooper's Emporium of Arts and Sciences," which furnished a plan on a very limited scale. The furnace proved successful, and enabled the Company to continue their manufacture of glass at a period when no foreign red lead was to be procured. They enlarged their works, until they have become the most important in the country; while for over thirty years they monopolized the business in all its branches, from the highest qualities of pure Galena and painter's red lead to common pig lead. In manufacturing metallic lead, its weight is materially increased by the absorption of oxygen gas. In 1847 the writer made many test experiments, one as follows: 660 pigs of blue lead, weighing 45,540 pounds, turned out from the ovens 48,750 pounds of litharge,—an increase in weight of 3210 pounds. The cost of labor was $65.50; fuel, $86.50; engine power, $17.50; total, $169.50; and the market value of the excess in weight of the lead was $250, showing a satisfactory profit to the company for their outlay in this branch of their business. Chemistry gives the increase in course of manufacture: In protoxide state, 7 per cent.; in deutoxide state, 11 per cent.; in tritoxide, 15 per cent. Muriatic acid will detect iron in lead, on dissolving a small piece of lead in the acid. If colorless, it is good. Nitric acid will detect if there is cobalt in the lead, by adding to the acid half the quantity of high-proof alcohol. If present, the evidence is soon seen. Some use the following as more direct:—In a small evaporating glass dish place say one ounce of lead; cover it with muriatic acid; dissolve the lead over a spirit lamp, add a little water, and let it settle; draw it off into another glass vessel, and add five or six drops of the solution of potash. If the lead is suitable for glass-makers, the solution will be of a light, clear, greenish color; if of a blue or purple shade, it is not suitable for flint-glass. SAND, OR SILEX.In the manufacture of glass it is essential that the silex should be perfectly pure, as the slightest mineral taint affects the color. At first the New England factories got their sand from Demerara, brought as ballast, and the quality was good. During the War of 1812 this source of supply was cut off, but Plymouth beach provided for the wants of the manufacturers, until a better sand was discovered at Morris River, N.J., though not up to the full requirement of the art. For ten years past, Berkshire County. Mass., has furnished sand; the best quality is owned by G. W. Gordon, Esq. By thorough washing, and passing it through fine sieves, and proper packing, he now commands the market, and delivers it ready for use. The purity has been tested, as shown by the following extract from a report by Professor A. A. Hayes, M.D., of Boston, Massachusetts State Assayer, of the result of analyses of three samples of Berkshire sand, taken from three different locations owned by Mr. Gordon, viz.:— "For the manufacture of glass, the slight amount of earth, in mica and tourmaline, contained in these samples, is of no account, the impurity being such oxides as color glass. The analyses therefore give only the proportion of coloring oxides; and, for simplicity of statement, the total weight of coloring oxide in each sample is determined in one part or pound.
"Sample B is equal in purity to the best sand known as a material for glass, in this or any other country." FURNACES.Next to pots, furnaces are most important for the success of a glass manufactory. Long ago it was seen that the old English plan was defective. They consumed coal at an extravagant rate, though this was not a serious drawback in England, because the furnaces were located near coal-mines, and run with a quality called slack, not otherwise merchantable. English furnaces were constructed with reference to durability, usually eight feet in diameter at the interior base, and six feet clear at the crown. This rule was followed in this country until 1840. The writer, having occasion to build an extra furnace, adopted the novel plan of one fourteen feet diameter at the base in the clear and only five feet at the crown, braced by binders, with cross-ties to prevent lateral expansion, which was a success. A furnace on the old plan consumed 2575 bushels of coal weekly, and refined only 38,000 pounds of raw material. The new refined 35,000 pounds, with a consumption of only 2000 bushels of coal. Since then a further decrease in consumption of coal has been produced by the use of the Delano patent, which feeds the furnace by forcing up the coal at the bottom of the burning mass, thus consuming the entire smoke, and obviating the necessity of wheeling coal on the glass-house floor and impeding the workmen. It also does away with all danger to the pots in feeding the fires. Besides these great advantages, it distributes a regular and uniform heat to each pot, causing the pots to last much longer, and fusing the metal better,—important items to mixers. From three to five tons of fuel is the weekly saving in a first-class furnace. It is of vital importance to obtain pots that will last a reasonable time. Clays of the finest quality are essential. Each piece must be freed from any foreign matter, particularly sulphate of iron, which often occurs. The burnt and raw clay should be well mixed, wet, and frequently kneaded, or trod over by the naked feet. Tenacity must be secured, sufficient that a roll twelve to eighteen inches long can be suspended, and hold firmly together by its own adhesiveness. The next point is to make the pots free from air blisters, all portions being compact; then to dry them thoroughly, which requires great care on account of the inequality of the different parts. Pot-makers are not agreed as to the value of different clays, and the use and proportion of raw to burnt shells. Some use sixteen parts raw to eleven burnt, some fifty-five raw to forty-five burnt, some equal proportions of each. Manufacturers have mainly depended upon imported clays, but the Western glass-makers have used Missouri clay with success. In the east it has not yet come into general use. Of the imported, that from Stowbridge is considered best. Garnkerk is a strong clay, and, if well selected, will rival any other. The analyses are for STOWBRIDGE,
GERMAN,
GARNKERK,
FRENCH,
WESTERN,
FUEL.This subject deserves special notice. We have said that the New England manufacturers at first used wood only, which was prepared by being split into equal lengths, with an average diameter of two inches, and then kiln-dried to dispel the sap and moisture. This fuel was supplied to the furnace at opposite fire-holes, a stick at a time, which was a laborious and heating process. Subsequently, a furnace was built at South Boston, over a cave, and unkilned wood was used in clefts. This saved one quarter in fuel, but it used up the pots so rapidly as to prove to be no economy in the end. After the development of the Virginia coal mines, our furnaces were altered to use coal, which proved to be more convenient and less costly than wood. The Pictou and Cumberland mines also increased the supply; and at present all the furnaces in New England, with one exception, are run with this last-named fuel. The various experiments made to economize fuel for the "glory-holes," as the workmen call the working places above the furnace, are well known. For many years the prepared wood we have spoken of was used. Then resin in a powdered state was added, which was both inconvenient and dangerous,—it having caused the destruction by burning of two glass-houses. This risk was finally overcome by the introduction of an invention which used it in a liquid state. But the demand for resin became so great as soon to more than double its price. This led to the substitution of coal tar, which was in use until science discovered its latent virtues for other purposes, and largely increased the original cost of the material. Indeed, at first the gas companies had considered it of no value, and had thrown it away by thousands of barrels. Combined with dead oil it is still used by glass-makers, but at greatly enhanced prices. The Cape Cod Glass Company have had in use for several years a Delano patent furnace-feeder, which enables them to use both hard and soft coal, as either is cheapest, and consumes the smoke and gas of either fuel, thus doing away all annoyance to the neighborhood. Theretofore every attempt to run working places with hard or soft coal had failed on account of the noxious gases set free, which injure the color of the glass. But owing to the intense heat created by the Delano patent, the furnace consumes these gases, and gives a quick fire polish to the various articles finished therein. As our native supplies of hard and soft coal are inexhaustible, there is no likelihood of an increase in the price of the present fuel so as to necessitate, as heretofore, a substitution of some cheaper article, especially as the discovery of petroleum tends to cheapen coal by a diversion of a portion of its consumption to that useful mineral oil. USEFUL ITEMS.A bushel of English coal weighs 80 pounds: of Virginia coal, 93 pounds; of Pictou, 76 pounds; of Cumberland, 84 pounds; of red ash, hard, 84 pounds. Crude saltpetre, refined, loses nine per cent. Chemists estimate that one hundred pounds of pearlash contain thirty per cent. carbonic acid. In refining, it loses on the average fifteen per cent. in weight. Phosphate of soda brightens glass. Borax brightens, but hardens glass. Twenty-five silver dollars refined will give thirty-seven ounces of nitrate of silver. A square foot of furnace clay weighs one hundred and twenty pounds. Alum, calcined, loses in weight sixty per cent. Crude flint batch, melted and ladled out, loses in the average fifteen per cent. in weight. Hard coal will measure forty cubic feet to a gross ton. Glass in water. There are some peculiar phenomena connected with hot glass and water. If a ball of red-hot iron is placed in a vessel containing cold water, the latter is quickly agitated. But a ball of melted glass of equal weight dropped in cold water will produce no immediate agitation. The water will remain for some time quiescent; but when the glass is cooled to about half its highest temperature, it agitates the cold water violently. Technical terms, descriptive of glass, such as crystal, flint, tale, may be derived from these facts: the French used for their base crystal stones, burnt and ground fine; in England they had recourse only to flint stone, treated the same as the French used their blocks of crystal; tale was derived from the mode of selling, the best glass being sold only by weight, while light articles were sold tale. Glass-making tools Transcriber's Note: Minor typographical errors have been corrected without note. Irregularities and inconsistencies in the text have been retained as printed. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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