Diamond powder is equally as important as “bort,” being used in nearly every stage of jewel-making. The coarsest charges the “skives” or saws used for splitting up the stone. These skives are made of soft sheet-iron, and act on the same principle as the laps. The finer grades, in bulk, resemble very much ordinary slate-pencil dust; indeed, the latter is often used as an adulteration. This powder is not uniform in fineness, and the jewel-maker is under the necessity of separating the different grades. This is effected by a simple process called “floating off,” and is conducted as follows: A certain quantity of powder, say a carat, is put into a pint of pure sweet oil, contained in some such shallow vessel as a saucer. Depending on the fluidity of the oil, the mixture, after being thoroughly incorporated, is allowed to stand undisturbed for about an hour or an hour and a half. During this time, owing to their greater gravity, the largest particles are precipitated, leaving held in suspension a powder of nearly uniform fineness. The mixture is now carefully decanted into another similar vessel, leaving the coarse powder at the bottom of the first. This coarse deposit is denominated No. 1, and is used for skives, laps, and other rough purposes. The decanted mixture in the second vessel is allowed to remain quiescent for twelve hours, when the same operation is performed; and the third vessel now contains most of the oil, together with the finest particles of powder. The precipitate from the second decantation is the ordinary opening powder; the finest being for polishing both the holes and outsides of jewels, and giving the final finish to the faces of pallets, roller pins, locking spring jewels, etc.
The good workman is careful to keep the powder in this condition as free as possible from any extraneous dust, and above all to preserve the different grades from any intermixture, as a small quantity of a coarser grade would destroy a finer one for all its purposes, and the process of “floating off” would have to be repeated.
The most important stone in jewelling, the diamond, becomes more of an agent of the manufacture than an object.
Properly, for jewelling the ruby and sapphire are pre-eminent; inferior only to diamond in hardness, possessing a sufficient degree of toughness, susceptible of an exquisite polish, this (for they are one and the same) stone is the favorite of the Swiss, English, and American, for all high class work—the Swiss, however, using it indiscriminately in all watches.
The ruby proper is of one color, but in its varieties of intensity may change to a very light pink. When still lighter it is ranked a sapphire, which comes in almost every possible color and shade, from ruby to a perfect transparent colorless crystal. This stone differs in degrees of hardness and capacity of working—the hardest being a greenish yellow, in the shape of pebbles, with very slightly rounded edges, difficult to work, but forming the strongest and most perfect jewel known.
It must be remembered that this description gives the value of the ruby and sapphire as a material for jewelling only. For ornamental jewelry, the value depending on color, of the most intense ruby or blue for sapphire, together with brilliancy and weight. The ruby and sapphire are formed on an aluminum base, the common emery being another form of structural arrangement, but of the same chemical constitution.
These stones possess every quality to make them the base of perfect jewelling; and still the chrysolite is equally in favor with most jewellers. It is not quite so hard, but it is more easily worked and cheaper in price, and it would be difficult to tell wherein it is inferior to either the ruby or sapphire. It has a yellowish tinge, verging to the color of the olive. As a stone for jewelry it is not fashionable, and only in Persia is it valued. There are, however, some very strong objections to its use by the workman; it is not uniform in hardness; in polishing it will drag, that is, the surface will tear up in the process. Unfortunately the eye is not able to detect the fault before working, and it is found only when much preliminary time and trouble has been expended. It is susceptible, when good, of a perfect polish, and is much used in chronometer work, especially for jewelling the 4th hole, as its non-liability to fracture renders it valuable.
“Aqua Marine” is a brother to the emerald, differing from it only in intensity of color, and composed of the same constituents. These two gems are the only ones in which the rare metal, glucinum, has been detected. It is extensively used in the American and English watches, but never in the Swiss. It is soft, not much harder than quartz, but comes in large pieces, perfectly transparent, and of a color which is that pure green of sea-water, from which it takes its name, “Aqua Marine.”
The garnet in English watches plays an important part for pallets, also for roller-pins; a very soft stone, but very porous. When set in the pallet with a pointed toothed wheel, it is apt to act as a file from its porosity, cutting the end of the tooth. This may be detected in any pointed tooth lever watch, by observing the color of the back of the tooth. “Black vomit” it used to be called in the Boston factory. Most of the garnet used is an Oriental stone, the best quality coming in bead form, the holes having been pierced by the natives. The cost of piercing the stone in Europe or America would be far above its value. The Oriental is the best for Horological purposes, though Hungary and Bohemia furnish the most highly prized stones used for ornamental purposes; indeed, in some German towns the cutting and setting of the garnet is a specialty, giving employment to a large number of people. And, strange to say, the best market for their sale is the United States.
This comprises about all the stones used in watch and chronometer jewelling. Still in clock work the pallets are generally jewelled in agate, a stone not at all suited to the purpose, it having, even in the best specimens, a decided stratification that prevents an uniform surface being formed by any process. The cornelian form of the agate is not open to this objection, and makes capital bearings for knife edges of fine balances, and compass stones for centres of magnetic needles. For watch or chronometer purposes the only really useful stones are sapphire, ruby, chrysolite, and aqua marine—all possessing peculiarities that deserve some remarks, as they are of the utmost importance to the hole maker. The sapphire is the hardest stone, next to the diamond, and yet specimens can be, and are found, so soft as to drag in polishing. Again, if stratified very clearly, will “fire crack” in opening the hole. The ruby is more uniform in its structure, and is more highly prized on that account; its hardness being all that is necessary, while its susceptibility of receiving a high polish is equal to that of the sapphire or chrysolite. The aqua marine is always uniform and may be polished both externally and in the hole with “tripoli,” saving something in diamond powder in the process of making. In our estimation, however, the chrysolite is the most valuable of all the stones. True, when purchased in the rough, many pieces will be found unfit for the jeweller’s purpose; but when the right quality is found, nothing can be better adapted to jewelling. Hard, it is easily wrought, taking a peculiar unctious polish, retaining oil in its most limpid condition for a long time.