The following receipt is often used for coating iron or steel, but it is not generally known among many of the craft that it may be used to prepare zinc for sketching, giving the zinc a dark coating. Dissolve 1 ounce sulphate of copper in 4 ounces water, add ½ teaspoonful of nitric acid and apply a thin coating to the zinc with a piece of waste. If used for iron or steel the work should then be rubbed dry. Care should be taken in handling and using the mixture, as it rusts iron and steel badly if left on.
Bronze may be renovated and recolored by mixing one part muriatic acid and two parts water, and applying the diluted acid to the bronze articles with a cloth. Before applying the acid the articles should be cleaned thoroughly from all grease. After having applied the acid let the article dry, and then polish with sweet oil.
E. W. Norton.
A very suitable and effective acid dip for bronze castings may be made up in the following manner. The constituents required are: One gallon pale aqua fortis, 1 gallon oil vitriol, 4 quarts of water, and 8 ounces of rock salt. In mixing the acids add the vitriol to the aqua fortis, after which the water should be introduced, by pouring it very slowly into the acid solution. Water should never be poured into the acids separately. When the water and acids have become thoroughly mixed, the salt may then be added. The solution becomes quite warm after mixing, which is a good time to add the salt, as the heated solution dissolves the salt readily. • After mixing, the solution should stand from 10 to 12 hours before using. It is best to make a large quantity of the solution if much dipping is to be done. To secure the best results it is necessary that the solution be kept at as low a temperature as possible, hence it is advisable to place the receptacle in a tank of cold water, or what is better, place it in running water. Urbana, Ill. T. E. O'Donnell.
Very often in the shop and also in the drawing room we want to lay out some piece of work for trial on something which will show fine accurate marks, but cannot obtain a piece of sheet zinc. I have used something which is just as good and more likely to be at hand, and that is a sheet of bright tin plate rubbed over with a piece of waste dipped in a sulphate of copper solution. This is made of water and blue stone with oil of vitriol added to the proportion 1 of vitriol to 50 water. Rub the tin thoroughly, keeping the waste wet with plenty of fresh solution and soon you will see spots of brass, then of copper, then a dark gray, nearly black, which wipe dry, and you will have an ideal surface to lay out on.
The above Is a kink which I have found very useful. F. W. Bach.
Ilion, N. Y.
The brass must be thoroughly cleaned, and then is heated slowly over a charcoal fire, care being taken not to allow the brass to touch the charcoal, or indeed not to allow any sparks from the charcoal to come in contact with the brass, as it will cause red spots. As soon as the brass is slightly red, dip it into nitric acid and reheat, just short of red. Rub strongly with a stiff bristle brush and clean with a greasy cloth. This gives a fairly permanent dead black finish. P. H. Oto.