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Watchmakers' Hand Book

Part II,
MATERIALS EMPLOYED IN HOROLOGY
Page 16

CEMENT, WAX, RESIN, ETC.

      190. The principal uses to which the watchmaker applies cement is for fixing objects in the lathe, pallet-stones in position, as well as locking and unlocking pallets, ruby-pins, etc.

      The selection of a cement or wax is not a matter of indifference; fine sealing-wax causes objects to adhere firmly together, but many of the best workmen prefer refined shellac. Certain kinds of wax are too dry, the consequence being that a false stroke of the graver will often detach the piece; others are thick and soft, and are apt to heat rapidly under the action of the burnisher or polisher, so that the object is displaced. It is only by making a series of trials that the efficiency of the material can be ascertained. Some workers claim that a mixture of sealing-wax and shellac gives good results.

      191. Mode of applying cements. When employing wax, resin, cement, etc., for uniting two objects, it is important to note that the mode in which it is applied has an important influence on its efficiency. The following observations on this point are due to M. Sibon, and the reader will be able to select those portions that have reference to his work.

      When two objects are united by a cement, this will lose much of its value if unskillfully applied, and, in order to use it to the best advantage, the following practical rules should be observed.

      1. The surfaces to be united must be quite clean.

      2. The less cement, wax, etc., that is interposed between them, the better they will adhere. This is owing to the fact that with a thick layer the object has, at the junction, no more rigidity than that of the cement itself; as a rule this more fragile than the material it is employed to unite.

      3. There should be perfect contact between the cement and the surfaces. With a view to securing this, the object must be first heated to a point such that the wax or cement cannot solidify without having first had time to effect a perfect union.

      This remark is especially applicable when using sealing-wax, mixtures of resin, shellac, and similar materials. They will not adhere firmly unless the surfaces have been heated very nearly to the point of fusion of the cement. The sealing of letters offers an example in proof of this assertion. When the seal has been used several times in succession or been left too long on the wax so as to become hot, it will adhere and cause some inconvenience if further employed.

      With hot melted glue, adhesion is best secured by friction or a moderate pressure.

      Sealing-wax is excellent for uniting metal to glass or stone, providing they are sufficiently heated to melt it; for, if applied to cool surfaces, it will not adhere at all. By heating two pieces of glass or stoneware sufficiently to melt shellac, a small quantity will suffice to make them adhere firmly together; notwithstanding that every one has seen such joints, very few succeed in making them, for the simple reason that they do not recognize the necessity of heating a delicate piece of glass or china to the point which is essential for securing a good result.

      In conclusion, the principal obstacles to adhesion are air and dirt. The fist is always present; the second is due to accident or carelessness. All surfaces are covered with a this layer of air that is very difficult to remove; its influence prevents highly polished metal from being moistened when immersed in water. So long as this layer of air is not displaced, the cement cannot adhere to the surface to which it is applied, because it cannot come into direct contact. The most effective agent for displacing this air is heat. Metals heated to about 75° C. (170° F.) are immediately moistened on being plunged into water, hence it follows that, as regard cements that are applied in a fused state, heat is the best means of bringing them into intimate contact with the surface.

      We would add that, in addition to possessing this advantage, the application of heat also renders the surfaces more penetrable to the layer of cement, after the manner of soldering, and makes the interlocking of the molecules more perfect; this explains the greater degree of tenacity of a well-made joint with only a thin layer of cement.

      192. To set in wax in the lathe. Trace a series of concentric circles on the face of the chuck with a graver point, after turning it true; this will increase the adhesion of the cement. Then the flame of the spirit-lamp is held under the rotating chuck and when this is hot enough, its surface is covered with a layer of shellac or sealing-wax, and the object is held against it. Holding it in position with a piece of pegwood supported on the T-rest, the lamp is removed and the lathe kept rotating until the cement sets. The cooling can be hastened by applying a small moist sponge, but it should not set too suddenly.

      If the object requires to be very exactly centered, its position must be insured while the cement is still soft by means of a long pegwood stick in its central hole. This stick is held in position until the cement sets, steadying it between two fingers close up to the chuck. The slightest eccentricity will be indicated by a motion of the free end of the stick.

      If the object is round, and has no central hole, it must be centered by its circumference, holding the pegwood in front, or resting against a corner of the circular elevation or depression, as, for example, the collet of a wheel, or of a cylinder riveted to its balance, etc.

      The beginner should make a number of trials; they will enable him both to acquire lightness of touch, and to recognize the proper degree of softness of the cement for centering, as well as its tenacity.

      When it is essential that the two faces of the object be strictly parallel, a precaution is necessary; this consists in leaving on the face of the chuck a slightly projecting circular rim with a fine smooth edge, and of a diameter rather less than that of the object. By moving this latter backwards and forwards after applying it to the wax, and pressing it into close contact while cooling, the requisite parallelism will be secured.

      193. To fix a pallet stone, etc., in position. To fix a pallet-stone or an end-stone by means of shellac it is usual to place a small piece of the latter round the stone when in position and apply heat. But very often the lac spreads unevenly or swells up; and this, in addition to being unsightly, is apt to displace the stone. The inconvenience can be avoided as follows: The pallets are held in long sliding tongs, and, taking a piece of shellac, heat it and roll it into a cylinder between the fingers; again heat the extremity and draw it out into a fine thread. This thread will break off, leaving a point at the end of the lac. Now heat the tongs at a little distance from the pallets, testing the degree of heat by touching the tongs with the shellac. When it melts easily, lightly touch the two sides of the notch with it; a very thin layer can thus be spread over them, and the pallet-stone can then be placed in position and held until cold enough. The tongs will not lose the heat suddenly, so that the stone can easily be raised or lowered as required. The projecting particles of cement can be removed by a brass wire, filed to an angle and forming a scraper.

      To fix an end-stone, the cap must be held by its edge in the sliding tongs, and shellac carefully applied around the edge of the hollow. It is advisable to hold the cap in a small tool formed of two parallel blades, as when reversed so as to press the stone on a flat surface, the shellac will spread over the end stone, from which it will be removed with difficulty.

ENAMEL.

      194. This name is applied to an opaque glass, with which various metallic compounds, such as oxide of tin, phosphate of lime, borax, etc., have been incorporated by fusion. The color, of course, varies with the substance so added.

      Willis recommends the following as a good white enamel for dials: silver sand, 14 parts; borax, 10 parts; red lead, 18 parts; niter, 2 parts; oxide of tin, 12 parts; flint glass, four parts; and binoxide of manganese, 1-50th of a part. But a good deal of care is requisite, both in selecting the materials and preparing the enamel, in order to insure a pure color of any desired shade; it is, therefore, often desirable to purchase the enamel ready prepared.

      In applying enamel, regard must be had to the relative dilatation of the metal to which it is applied, the two being so combined as to expand and contract together; otherwise there is danger of the enamel cracking, either at once or shortly after it has set.

      Enamel may be applied to gold or copper. Associated with the latter, it forms the ordinary dials of watches and timepieces, and, with the former, it serves for making enameled gold dials or cases. The gold should be of 22 carat, the 2 carats of alloy consisting of equal parts of silver and copper. If the gold is of a higher standard, it will not adhere so well, and, if lower, there will be a further danger of melting the metal before the enamel is fused.

      Silver is apt to cockle on the application of heat, and enamel applied to it presents a bubbly appearance.

      195 Application of enamel in the cold. We are indebted for the following particulars to M. Fournier, of Dieppe, a will-known enamel maker:

      There are two kinds of false enamel for application, when cold, to damaged dials.

      The first, a mixture of white resin and white lead, melts like sealing-wax, which it closely resembles. It is advisable, when about to apply it, to gently heat the dial and the blade of a knife, and, with this, to cut a piece of enamel of the requisite size and lay it on the dial. The new enamel must project somewhat above the old. When cold, the surface is levelled by scraping, and a distance from the flame of a spirit lamp. It is necessary to be very careful in conducting this operation, as the least excess of heat will burn the enamel and turn it yellow; it is, however, preferable to the following, although more difficult to apply, as it is harder and does not become dirty so soon.

      The second false enamel contains white lead mixed with melted white wax. It is applied like a cement, neatly filing up the space, and afterwards rubbing with tissue paper to produce a shining surface; if rubbed with a knife blade or other steel implement its surface will be discolored.

PRECIOUS STONES.

      196. The principal precious stones used in watches. chronometers and regulator clocks, in their order of hardness, are: diamond, ruby, sapphire, chrysolite.

      A watchmaker, although he may not have had any previous experience of jewels, can easily ascertain their relative hardness by rubbing one against the other. The softer will be scratched by those that are harder, and the stone that can be marked by a file may be thrown aside as useless.

      197. Diamond. We shall make a very brief reference to this stone, as it is not used except for the endstones for balances for chronometers and high-class watches.

      Splinters of diamond are employed for drilling materials of a less degree of hardness, and fragments fixed at the end of a rod are used for turning very hard steel; diamond dust is the principal material used for working precious stones, polishing, etc. (see articles 165 and 169).

      198. Ruby. This jewel, of a rich, velvety, red color, exists in three principal varieties: oriental, spinel and balas rubies, which differ as regards their chemical composition.

      From a jeweler's point of view, the value of a ruby is enhanced by its rich color and transparency; but this is not the case in regard to its application in horology, for which hardness and capability of taking a high polish are mainly necessary.

      The specific gravity of the three varieties is: oriental, 4.2; spinel, 3.7; balas, 3.6.

      The first of these is the best, since it is the hardest, both taking a better polish in the first instance and retaining it for a longer period.

      In comparison with the other varieties, its specific gravity is greater and it possesses a brighter color, but will often be found to be less transparent.

      Spinel and balas rubies are frequently met with that are very beautiful to the eye, but their hardness is inferior to that of the sapphire and even the chrysolite. They must be carefully excluded from all good work, for, either in consequence of the inferior hardness or the mode in which the oxide of iron, magnesia, etc., is combined, or of other causes, oil rapidly deteriorates in contact with them, and the moving parts, especially if they are of steel, soon show wear. The rubies themselves also suffer, and it is by no means uncommon, especially in the case of duplex escapement, to meet with such jewels quite rough and even pitted on their acting surfaces.

      199. False ruby. In a certain class of watches, a variety of stones pass for rubies that are known to jewelers as rubicelle, rubace, rock ruby, Brazil, Siberian or Bohemian ruby, rose ruby, etc., the hardness of which is even less than that of rock crystal. Pivot-holes made of these imitations of the real ruby are worth less than plain brass settings

      200. Sapphire. The color of this stone, sometimes even milky, passes through all the shades of blue. Like the ruby, there are several varieties that differ appreciably in regard to hardness. The hardness of oriental sapphire is equal to that of oriental ruby; both consist of nearly pure alumina, colored by a little oxide of iron; their chemical composition thus being the same, they only differ in regard to color. It is, then, a great mistake on the part of watchmakers to prefer spinel or balas rubies in place of the oriental sapphires.

      The sapphire is more brittle than the ruby.

      The other kinds of sapphire, such as water sapphires, are not true sapphires; they are soft and should never be used in horology. The density of the oriental sapphire is about 4.01, whereas that of other kinds is only 2.58.

      201. Chrysolite. Under this name lapidaries include a variety of stones of yellow-green, apple-green with shades of yellow, and other colors.

      That known as oriental chrysolite, which is the same as the oriental topaz, has a beautiful pale yellow color with shades of apple-green; it is the most highly esteemed. This stone has a sufficiently high degree of hardness for use in watchmaking, as it will scratch rock crystal. Its density varies from 3.73 to 3.00.

      The other varieties, ordinary chrysolites, come very low in the scale of hardness. They can be scratched by quartz, rock crystal and even by the file, and are thus of no use for watches.

      202, Agate, Carnelian, Topaz. Only the varieties of the stones already considered that are termed oriental can be used for the pivot-holes or the pallets of astronomical regulators, but for the escapements of the ordinary time-pieces of commerce, such, for example, as the pallets of Brocot escapements, the topaz, agate or carnelian may be used. When of the hardest kind, and capable of receiving a high polish, they will very efficiently resist the friction of brass teeth. As to the softer kinds, they are inferior to hardened polished steel for pallets.

Submitted by: Samuel Kirk (##)

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