To produce a bronze finish on rough yellow brass castings, mix equal parts of nitric acid, sulphuric acid and water; the nitric acid and water should be mixed first and the sulphuric acid added slowly. Dip the yellow brass castings into boiling water a moment, then in the acid solution, then quickly back into the boiling water, and rinse thoroughly in clean water. Dry in pine sawdust. The castings must be perfectly free from soldering solutions, etc., or stains are liable to appear. This method gives a finish similar to gas fixtures, etc., and may be rendered very permanent by coating with a transparent lacquer.
I. W. Antano.
In the plating of brass or cast iron, or other porous metals, there is more or less trouble with what is called "spotting out" which is caused by the cyanide getting into the pores, and it has been hard to find a satisfactory remedy for this trouble. The following can be used with good results: First, give the work a good stiff coat of nickel, then put it through a brass solution without buffing. After the required deposit has been obtained, rinse it in cold water, and then hang in boiling water, as long as possible without tarnishing. Then hang it in a good hot oven until thoroughly dried out, after which buff and hang for a few moments in gasoline, and put it in the oven again. You will find this will cure a great deal of the trouble experienced on that class of work. This is a valuable process and one never before printed.
Bridgeport. Conn. J. L. Lucas.
This paste is used for silvering the scales on thermometers and the dials for clocks, aneroid barometers, steam gages, etc.
Put in an ordinary tea cup or other suitable vessel, 1 ounce of silver - coin silver will do, but pure silver is better and cheaper. Pill the cup half full of nitric acid, and place it in a vessel containing water, which must be heated. As the acid heats, it throws off fumes in shape of a brown smoke, very poisonous. When the smoke ceases to appear, add a teaspoonful of common table salt, and when the fumes caused by this cease, take the cup from the heat immediately and fill slowly to the top with cold water. Allow the white powder that will now be found in the cup to settle to the bottom and then slowly decant the liquid. When almost empty, fill again with cold water, and decant again, repeating this process at least half a dozen times. Mix the powder (commercial chloride of silver will do instead) with 10 pounds table salt, and ½ pound cream of tartar. Mix thoroughly dry, then add enough cold water to make a paste. Add the water slowly so as not to get in too much. Keep in a covered vessel and from the light.
The graduation marks, figures, and letters, stamped or cut into the work may be filled with ordinary roofing tar, which is applied by heating the work enough to melt the tar. Most of the surplus tar may be scraped off with the edge of a card, or any cardboard handy. This filling stands better than sealing wax, and will not dissolve and blur when lacquered if the lacquer is put on properly. Another filling is japan, which is applied with a brush cold, and cleaned with a card as before. It is then baked, and when the work is finished, the filling will be found to be glossy and permanent and will not be dissolved by any lacquer or heat.
The piece to be silvered should be thoroughly cleaned with emery cloth or paper just before applying the paste, which is to be put on by hand and rubbed well in the surface of the work. After this is done, the work should have a dirty, silvery yellow tinge, which will be brightened by rubbing with a dry mixture of ½ pound cream of tartar and 10 pounds salt well mixed. The work should be thoroughly washed to clear it of the surplus salt and then dried in sawdust and lacquered. I have used this method for silvering over 30,000 steam gage and clock dials, and many other dials and scales; hence I know it is all right.
Brooklyn. N. Y. J. S. Gordon.