The satin effect may be obtained on a dial by prolonging the acid dip and otherwise proceeding as before. Many of these dials were of zinc and all that applies to brass or copper may be also executed in zinc, but in plating it will be found necessary to plate two or three times, as the single coating will apparently disappear into the zinc unless it is given a heavy deposit of copper in a plating bath. Where it is desired to obtain a bright gold color, the gold plating solutions now sold for the coloring of jewelry may also be used on either of these metals. For the reasons given above, however, they are not very successful on a zinc base.
Many of the cheap clocks have paper dials glued on a zinc plate and when the dial is soiled the repairer cleans them up by pasting another dial on top of the original. These dials are made on what is known as lithographic label paper; that is paper which is waterproof on one side, so that it will not shrink or swell when dampened. In addition to the lithograph coating they are generally given a varnish of celluloid by the clock manufacturers, thus making them practically waterproof. They are very cheap and the repairer will find that he will obtain in prestige from such new dials far more than they cost.
Tarnished metal dials are best cleaned by a dip of cyanide of potassium, of about the same strength as that used for cleaning silver. If the tarnished parts have been gilded, however, the cyanide should be excessively weak. Mining men use a cyanide solution for the recovery of gold, which is only two-tenths of one per cent cyanide, and this will collect all the gold from ore that runs from $10 to $15 to the ton, the pulp in such cases being left in the solution from seventy to ninety hours. The ordinary cyanide dip for the jeweler is one ounce to thirty-two of water, while the miner’s solution is two-tenths of an ounce to one hundred ounces of water. You can see that with the strong cyanide solution the gilt surface will all be taken off unless very rapid dipping is strictly followed by thorough washing.
A novelty which keeps periodically coming to the front, say about once every ten years, is the luminous dial. This is done by painting the dial with phosphorus or a phosphorescent powder. Then when it is placed in the light it will absorb light and give it off in the dark until the evaporation of the phosphorus.
The composition and manufacture of this phosphorescent powder is effected in the following manner: Take 100 parts by weight of carbonate of lime and phosphate of lime, produced by calcination of sea-shells, especially those of the tridacna and cuttlefish bone, and 100 parts by weight of lime, rendered chemically pure by calcination. These ingredients are well mixed together, after which 25 parts of calcinated sea salt are added thereto, sulphur being afterward incorporated therewith to the extent of from 25 to 50 per cent of the entire mass, and a coloring matter is applied to the composition, which coloring matter consists of from 3 to 7 per cent of the entire mass of a powder composed of a mono-sulphide of calcium, barium, strontium, magnesium or other substance which has the property of becoming luminous in the dark, after having been impregnated with light. After these ingredients are well mixed, the composition is ready for use. Its application to clock dials is made either by incorporating suitable varnish therewith, such as copal, and applying the mixture with a brush to the surface of the dial, or by the production of a dial which has a self-luminous property, imparted to it during its manufacture. This is effected in the following manner: From 5 to 20 per cent of the composition obtained and formed as above described, is incorporated with the glass while it is in a fused state, after which the glass so prepared is molded or blown into the shape or article required. Another process consists of sprinkling a quantity of the composition over the glass article while hot, and in a semi-plastic state, by either of which processes a self-luminous property will be imparted to the article so treated.
Where enamel dials are chipped the cracks may be hidden by first pressing the cracks very slightly open and washing out. Then work in a colorless cement to fill the crack, allow to dry and stone down. Where holes have been left by the chipping, melt equal parts of scraped pure white wax and zinc white and let it cool. Warm the dial slightly and press the cold wax into the defective places and scrape off with a sharp knife and it will leave a white and lustrous surface. If too hard add wax; if too soft add some zinc white.
Varnish for Dials, Etc.—A handsome varnish for the dials of clocks, watches, etc., may be prepared by dissolving bleached shellac in the purest and best alcohol. It offers the same resistance to atmospheric influence that common shellac does. In selecting bleached shellac for this purpose be careful to get that which will dissolve in alcohol, as some of it being bleached with strong alkalies, is thereby rendered insoluble in alcohol. The shellac when dissolved should be of a clear light amber color in the bottle and this will be invisible on white paper when dry.
Colorless celluloid lacquer, known to jewelers as “silver lacquer” on account of its being used to prevent tarnish on finished hollow ware, also makes a good varnish to apply to dials, either metallic or painted. It is best to have it thin, flow it on the dial and then level the dial to dry.
Success in the repairing of a broken enameled clock dial will greatly depend upon the practical skill of the operator, as well as of a knowledge of the process. If it is only desired to repair a chipped place on a dial, a fusible enamel of the right tint should be procured from a dealer in watchmakers’ materials, which, with ordinary care, may be fused on the chipped place on the dial so as to give it a workmanlike appearance when finished off. The place to receive the enamel should be well cleaned, and the moist enamel spread over the place in a thin, even layer; and, after allowing it to dry, the dial may be held over a spirit lamp until the new enamel begins to fuse, when it may be smoothed down with a knife. The dial, after this operation, is left to cool, when any excess of enamel may be removed by means of a corundum file, and subsequently polished with putty powder (oxide of tin). The ingredients of enamel, after being fused into a mass, are allowed to cool, then crushed to powder and well washed to get rid of impurities, and the resulting fine powder forms the raw material for enameling. It is applied to the object to be enameled in a plastic condition, and is reduced to enamel by the aid of heat, being first thoroughly dried by gentle heat, and then fused by a stronger one. The following is a good white enamel for dials:
Silver sand, 3 ounces; red lead, 3¾ ounces; oxide of tin, 2½ ounces; saltpeter, ½ ounce; borax, 2 ounces, flint glass, 1 ounce; manganese peroxide, 2 grains. The basis of nearly all enamels is an easily fusible colorless glass, to which the required opacity and tints are given by the addition of various metallic oxides, and these, on being fused together, form the different kinds of vitreous substances used by enamel workers as the raw material in the art of enameling.