_How to put a thin coating of colouring on the surface of metals by
chemicals:_ A great variety of shades may be obtained simply through
heat. The colours ordinarily produced on copper articles by means of
heat come through the polishing. Any metal whose surface is highly
polished will take on a number of different colours, beginning at a
straw colour and changing to a dark straw, purple, dark blue, light
blue, and steel or gray, by heating the piece to be coloured to a
temperature of 630° F.
_Barium sulphide and water (a very good composition for colouring
metal):_ Immerse object until it assumes desired tint from light
brown to violet to black. Heat gently over bunsen flame until a rich
deep violet appears. After it is cool rub with soft cloth.
_Patina imitation (a very good composition for the greening of copper):_
1 part sal. ammoniac,
3 parts cream tartar,
6 parts salt,
12 parts hot water,
2 parts nitrate of copper.
Saturate soft cloth and rub or sprinkle the solution on the copper. Let
stand in the open air ten or twelve hours. Wash the colour off with
clear cold water. Tone down to suit.
Another way of colouring metal.
Silver.
_To oxidize silver:_ The following is a solution commonly used for
oxidizing silver:
Potassium sulphide, 5 grains,
Water, 10 fluid ounces.
The variety known as liver or sulphur is generally used, and imparts a
reddish brown colour to the silver, the colour being darker the darker
the solution. It should be worked at 60 or 70 per cent. The stronger
the solution the blacker the colour. If ammonium carbonate (20 grains)
is added to the above formula and is worked hot, a black colour appears
upon rubbing with a very fine wire brush. It takes on the colour of
black lead.
_Colouring of brass:_
Copper sulphate, 2 ounces;
Water, just sufficient to dissolve the copper sulphate;
Ammonia, to neutralize and make slightly alkaline.
This will turn brass a very beautiful blue-black colour. Copper assumes
a very beautiful tint from this solution.
_Cement for engravers:_ Melt best pitch in an iron pot and when
completely liquid stir in a mixture composed of two thirds of raw pitch
and one third plaster of paris. Make a lot of ten pounds. Add one half
pound mutton tallow, boil and mix thoroughly. Should this be too soft,
add plaster of paris until you get the desired hardness:
5 lbs. black raw pitch,
5 lbs. plaster of paris,
1-1/2 lbs. mutton tallow.
_To polish enamel:_ After rubbing it down with the corundum file, take
a small rod of tin or pewter and after anointing it with fine Tripoli
or rotten-stone, grind the surface of the enamel evenly with the tin
or pewter rod. Next take a stick of lime wood and use that with the
rotten-stone in the same way and finish with putty powder and stick
covered with chamois skin.
_To unsolder a piece of work:_ Paint those joints which are not to be
unsoldered with a mixture of clay water, to which add a little common
salt. When dry, scrape the part to be unsoldered and paint it with
borax. Now heat till solder melts, pick off with pliers or knock it off
with a gentle tap. The borax adds flux, thus helping the solder to run
at a melting temperature.