Practical Magazine 20, 1876
(Chemistry applied to the Arts, Manufactures, &c.
Metallurgy.)
M. F. DIETLEN’s process for the above purpose is as follows. When the articles, such as those used in gas apparatus, are completed, they are slightly re-heated to get rid of all trace of grease. If that is not possible on account of the solder or their form, the cleaning is performed by brushes impregnated with potash or soda lye, and the articles are dried with very dry sawdust. After this they receive a dull coating, and the projecting parts are polished with the burnisher. For polishing, grease should not be used, but simply pure water. Lastly, the articles should be brushed with chalk, subjected to flame of charcoal or alcohol, and varnished with a palette pencil or by immersion.
For the dull coating equal parts of sulphuric acid and nitric acid should be used, care being taken to put a piece of zinc in the mordant liquid during the operation. When the articles are of bright or greenish brass they must first be coloured red, which is easily done by heating them in a bath of tartrate of potass. After the coating they should be well washed with plenty of water, lest they should be covered with spots.
The varnish is made by dissolving 65 grammes (2¼ oz.) of gum lac of a clear brown colour in a mixture of half a litre (rather more than three-quarters of a pint) of alcohol, and the same quantity of spirit of wine, and adding four soup spoonfuls of turmeric flour. The whole should be exposed in a warm place for twenty-four hours, and filtered through felt. If the articles are dried a little every time a layer of varnism is deposited, the latter will form a covering of a bright gold colour, which will not be injured by being often handled.
- Dingler's Polytechnisches journal.
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