Watch and Chronometer Jewelling.
This whole subject is well worthy an article both in a scientific and mechanical sense, whether we consider the delicacy of the operations or the intractable character of the material operated on—for there has been no improvement in the horological trade of more importance to accuracy and durability of time-keepers.
The substitution of stone for common brass or gold bearings, was prompted by the inevitable wear of the holes from frequent cleaning, and the abrasion of the pivots, produced by the accumulation of dust with viscid oil; the pivot being cut away, or the hole opened too large. So long as the verge and cylinder were the prevailing escapements, the necessity for jewelling was not so strongly felt, except in the balance holes. The introduction of the lever escapement brought with it a better watch,—capable of more accurate time, but demanding an improved construction.
An Italian, in 1723, first introduced the practice of using stone for bearings. He not only conceived the idea, but was successful as an artisan in making his own jewels; ingenious and skilful as he was, however, he encountered obstacles almost insurmountable.
The art of cutting gems, it is true, was at that time well understood, but no one had attempted to drill a hole in a hard stone fine enough for a properly sized pivot. The watches at that time that were jewelled could boast of nothing more than the balance holes, and they were not pierced to let the pivotthrough.
It is a very difficult matter to polish a taper indentation in a stone, even with modern appliances,in consequence of the tendency to create atitat the bottom,—thus throwing the balance staff out of upright. The difficulties in the then state of knowledge retarded the general introduction of stone-work for many years. The Swiss, however, seeing the advantages derived, finally struck out the various manipulations with success. Time and experience gave more skill, and at the present time it is impossible to find a Swiss watch, even of the cheapest class, that is not jewelled in at least four holes. The English trade adopted the art later; but even then it did not become general for many years. Within a generation, only fine English levers were jewelled.
The mere substitution of a harder substance was not the only improvement; other conditions necessary to accuracy were insured. The hole could be maderound—the material of such a character that no chemical action could be effected on the oil used for lubrication, and the vertical section of the hole could be made so as to present the least amount of frictional surface, yet still giving a perfectly polished bearing, thus avoiding the cutting of the pivot.
The whole “modus operandi” from the stone in the rough to the last setting up is well worth the attention of the watch repairer, and certainly that of the manufacturer.
Of the materials used in the trade, the first and most important is the diamond, used only in the time-piece as an end-stone—but at the bench all-important, as a means of making the other jewels. The diamond possesses the requisite susceptibility of polish, combined with greatest hardness of any substance known; but this adamantine quality precludes its being pierced with a through hole. Considered chemically, the diamond is pure carbon,—its different varieties differing only in structure—common charcoal, its lowest—plumbago, its intermediate grade. Another variety, called the “black diamond,” or “diamond carbon,” occurs, which is interesting as being a parallel with emery, compared with crystallic sapphire. The form of diamond most in use for mechanical manipulations, is almost always crystallized; yet it will be seen that the agglomerated form of diamond carbon plays no unimportant part in jewelling. As a jewel, no use is made of the diamond, other than as an end-stone. Marine chronometers, in which the balance will weigh from five to nine pennyweights, are almost invariably furnished with a diamond end-stone, set in steel. Yet, hard as the substance is, it is often that a pivot will cut an indentation in its face. The cause of this apparent anomaly is to be found in the structural character of the gem, and its value. The lapidary, saving in weight as possible, does not care, in “Rose Diamonds,” to pay attention to the lines of cleavage. If the face of the stone makes a slight angle with the strata of the jewel, there occur innumerable small angles of extreme thinness—the pivot, coming in contact with any of these thin portions, may fracture it, and the fragment, becoming imbedded in the tempered steel pivot, becomes a drilling tool. In our experience we have had marine chronometers sent for repair, that have lost their rate so much as to become utterly unreliable from this cause alone—the pivot having produced an indentation of the stone, creating more friction, and thus destroying the accuracy of the instrument.
As a general rule, the rose diamonds sold for this purpose are sufficiently good for general work. In a very fine watch or chronometer the stone should be selected with reference to its polish on the face, and its parallelism in the lines of cleavage. The diamond, however, gets its great importance from being the only agent we can use in working other stones. Without it the whole art of jewelling would not be practicable. The various steps are all connected some way with diamond in its different shapes. “Bort,” the technical name for another variety, is merely fragments of the stone that have been cleaved off from a gem in process of cutting, or gems that have been cut, but found too full of flaws to become of use for ornamental jewelry purposes, the cost depending on the size, varying from $5.50 to $18 per carat. This “Bort” is used as turning tools—the larger pieces being selected and “set” in a brass wire and used on the lathe, in the same manner, and with the same facility, as the common graver. For tools, even the diamond is not of equal value—apure white and crystalline in structure generally being too brittle (though hard) to endure the work. Among the workmen the “London smoke,” a clouded, brownish stone, is most prized—it possessing the twofold qualities of toughness and hardness.
Another form of “Bort” comes in the shape of a small globule, sometimes the size of a pea; it is crystallic, and when fractured generally gives very small, indeed minute pieces of a needle shape. These are carefully selected, and form the drills with which the English hole-maker perforates the jewel. These drills, when found perfect, for soundness, form, and size, are very highly prized by the workman, as the choice of another, together with the setting, will often take a vast deal of time and labor.
“Bort” is also used in the making of the laps or mills with which the jeweller reduces the stones to a condition for the lathe and subsequent processes. For this purpose such pieces as are not fit for cutting-tools, or drills, are selected. A copper disk, having been first surfaced and turned off in the lathe, is placed on a block or small anvil; each piece of stone is then separately placed on the copper, and driven in with a smart blow—care being taken that no place shall occur in the disk that does not present, in revolution, some cutting point. It would seem impossible to retain the diamond fragment, but it must be remembered that the copper, being a very ductile metal, receives the piece; the first rubbing of a hard stone then burnishes the burred edges of the indentations over every irregular face of the diamond, leaving only a cutting edge to project. The rapidity with which such a lap, well charged, will reduce the hardest stone, is somewhat marvellous. It is the first tool used in jewelling, and so important that a more detailed and explicit description of its make will be given when the process of manufacture is treated upon.
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 denominatedNo.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 willdrag, 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 todragin 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 tothat 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 peculiarunctiouspolish, retaining oil in its most limpid condition for a long time.
These stones form the general stock by and from which jewels are made. The details of the various manufacturing manipulations, the tools used, also the setting in the work, together with the important item of the screws, will form the subject of the next article on Watch and Chronometer Jewelling. Not having been able to get our engraving done in time for publication, we are compelled to reserve the remainder for the next number.