Black asphaltum mixed with a little wax or pitch, or even watchmakers’ cement, used to fasten staffs and pinions into a lathe for turning, is also used on these dials and with a sufficient proportion of wax or pitch it prevents shrinking and forms a very satisfactory dial with the single exception that it cannot be cleaned with benzine or hot potash, which will dissolve the enamel. Shoemakers’ heel ball is also used for repair jobs. In order to make either of these stick, the brass or copper plate is heated up so as to “hiss” as will a laundry flat iron when touched with a wetted finger, and a cement stick is rubbed over the letters to fill them; the excess of filling can be scraped off with an ivory scraper when at the right temperature—a little below the boiling point of water. Such filled letters can be lacquered over by going very quickly over the work so as not to dissolve the shellac in the cement.
Another way is to fill the letters with black lacquer. For quick repairs this is probably as good as any. Many of the old grandfather clocks have been filled in with a putty made with copal varnish and some black pigment. All putties shrink in drying and consequently crack and finally fall out. The wax and pitch are not subject to these disadvantages. If the plates are to be polished, polishing should precede the filling in of the letters, else the work may have to be done all over again. Black sealing wax and alcohol are also used, applied as a paint with a fine brush.
If the dial is to be silvered or gilt the blacking should be done first, and if to be electroplated the blacking should be what is known as the “platers’ resist,” which is composed chiefly of asphaltum and pitch dissolved in turpentine. It is also called “stopping-off ” varnish, and has large use in the plating establishments to prevent deposition of metal where it is not desired.
The repairer who gets many grandfather clocks will often find that it is necessary to repaint the dial, generally because of a too vigorous scrubbing, or because of cracks or scaling, which the owner may dislike. It is always best, however, to be cautious in such matters, as many people value such a clock chiefly on account of its visible evidences of age and such cracks form generally a large proportion of such evidence. Therefore it is best never to touch an antique dial unless the owner desires it.
Such dials are usually sheet-iron, and tolerably smooth, so the metal will need but a few coats of paint to prepare it. For ground coats, take good, ordinary white-lead or zinc white, ground with oil, and if it has much oil mixed with it pour it off and add spirits of turpentine and Japan dryer—a teaspoonful of dryer for every half pint of paint. The test for the paint having the right amount of oil left in it is, it should dry without any gloss. Rub every coat you apply with fine sand paper, after it is perfectly dry, before applying the next coat of paint. For the final coat, lay the dial flat and go over it with French zinc white. This coat dries very slow, and for a person not used to such work, is hard to manage. The next best (and for ordinary clock or watch making the best) for the last pure white coat is to take a double tube of Windsor & Newton’s Kremnitz white, thinned with a little turpentine. Such tubes as artists use are the kind. Apply this last white coat with a flat, camel’s hair brush. The tube-white should have turpentine enough added to cause it to flow freely, and sink flat and smooth after the brush. The letters or figures should be painted with ivory-black, which is also a tube color. This black is mixed with a little Japan, rubbing varnish and turpentine, and the lettering is done with a small, sign writer’s pencil. Any flowers or ornaments are painted on at the same time; and after they are dry the dial should be varnished with Mastic or Damar varnish or white shellac. All kinds of coach (Copal) varnish are too yellow.
Painted dials on zinc will blister and crack off if subjected to extremes of heat and cold, unless they are painted with zinc white instead of lead for all white coats. The reason is the great difference in expansion between lead paint and metallic zinc. This case is similar to that of using an iron oxide to paint iron work of bridges, ships, etc., where other oxides will chip and scale off.
The metal dials on these old clocks were silvered by hand. When you get such a dial, discolored and tarnished, it can be cleaned in cyanide and resilvered, without sending it to an electroplater, by the following formula:
Dissolve a stick of nitrate of silver in half a pint of rain water; add two or three tablespoonfuls of common salt, which will at once precipitate the silver in the form of a thick, white curd, called chloride of silver. Let the chloride settle until the liquid is clear; pour off the water, taking care not to lose any chloride; add more water, thoroughly stir and again pour off, repeating till no trace of salt or acid can be perceived by the taste. After draining off the water add to the chloride about two heaped tablespoonfuls each of salt and cream of tartar, and mix thoroughly into a paste, which, when not in use, must not be exposed to the light. To silver a surface of engraved brass, wash the surface clean with a stiff brush and soap. Heat it enough to melt black sealing wax, which rub on with a stick of wax until the engraving is entirely filled, care being taken not to burn the wax. With a piece of flat pumice-stone, and some pulverized pumice-stone and plenty of water, grind off the wax until the brass is exposed in every part, the stoning being constantly in one direction. Finish by laying an even and straight grain across the brass with blue or water of Ayr stone. Take a small quantity of pulverized pumice-stone on the hand, and slightly rub in the same direction, which tends to make an even grain; the hands must be entirely free from soap or grease. Rinse the brass thoroughly, and before it dries, lay it on a clean board, and gently rub the surface with fine salt, using a small wad of clean muslin. When the surface is thoroughly covered with salt, put upon the wad of cloth, done up with a smooth surface, a sufficient quantity of the paste, say to a dial three inches in diameter a piece of the size of a marble, which rub evenly and quickly over the entire surface. The brass will assume a greyish, streaked appearance; add quickly to the cloth cream of tartar moistened with water into a thin paste; continue rubbing until all is evenly whitened. Rinse quickly under a copious stream of water; and in order to dry it rapidly, dip into water as hot as can be borne by the hands, and when heated, holding the brass by the edges, shake off as much of the water as possible, and remove any remaining drops with clean, dry cloth. The brass should then be heated gently over an alcohol lamp, until the wax glistens without melting, when it may be covered with a thin coat of spirit varnish, laid on with a broad camel’s hair brush. The varnish or lacquer must be quite light colored—diluted to a pale straw color.
It is now possible to buy silver plating solutions which can be used without battery and they will produce the same effect as the formula just given. If they happen to be in stock for the repairing of jewelry they may be used in cleaning the dials, but as this is liable to fall into the hands of many who are far from such conveniences, we furnish the original recipe, which can be executed anywhere the materials can be obtained.
If the dial is of brass, very good effects have been produced by stopping off portions of the dial in an ornamental pattern before silvering, and then lacquering after removing the resist. But for a plain black and brass dial a dip of strong sulphuric acid two parts, red fuming nitrous acid one part, and water one part, mixed in the open air and dipped or flowed over the dial, forms what is known as the platers’ bright dip. After dipping the article should at once be rinsed in hot water and dried, and lacquered at once with a lacquer of light gold color. This makes a very neat and durable finish.