By E. PULCHER.
The French brass castings and articles of sheet brass are made of cheap,
light colored brass, and possess a fine golden color which is not
produced by gold varnish, but by a coating of copper. This gives them a
finer appearance, so that they sell better.
This golden color can be easily produced at very little expense and with
but little trouble by the following process. Fifty grammes of caustic
soda and 40 grammes of milk sugar are dissolved in a liter of water
and boiled for a quarter of an hour. The solution is clear as water at
first, but acquires a dark yellow color. The vessel is next taken
from the fire, placed on a wooden support, and 40 grammes of a cold
concentrated solution of blue vitriol stirred in. A red precipitate of
suboxide of copper is at once formed, and by the time the mixture cools
to 167° Fahr., the precipitate will have settled.
A suitable wooden sieve is placed in the vessel, and on this the
polished articles are laid. In about one minute the sieve is lifted up
to see how far the operation has gone, and at the end of the second
minute the golden color is dark enough.
The sieve and articles are now taken out, and the latter are washed
and then dried in sawdust. If the brass is left longer in the copper
solution, in a short time a fine green luster is produced, becoming
yellow at first and then bluish green. After it turns green, then the
well-known iridescent colors finally appear. To obtain uniform colors
it is necessary that they be produced slowly, which is attained at
temperatures between 135° and 170° Fahr.
The copper bath can be used repeatedly and can be kept a long time if
bottled up tightly without change. After it is exhausted it can be
renewed by adding 10 grammes of caustic soda, replacing the water that
has evaporated, heating to boiling, and adding 25 grammes of a cold
solution of blue vitriol.
Similar operations with other well known reducing agents, such as
tartrate of soda, glycerine, etc., do not give such good colors, because
they do not precipitate the copper solution so rapidly and at so low a
temperature.
If the rinsed and pickled brasses are dipped for five minutes in a three
per cent. neutral solution of cocoa nut oil soap, and then washed with
water again before they dry, the coating gains in permanence.
Brass articles that have to be cleaned frequently should be covered with
oil of turpentine, or thin English copal varnish.--_Neueste Erfind_.
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