This problem introduces engraving and enamelling, two interesting but
somewhat difficult operations. The process to be carried out is as
follows: Using 12-gauge copper, saw the outline, and apply the design
for the part to be enamelled to the copper by sketching it with a
pencil or transferring it by means of carbon paper. Then strengthen the
pencil or carbon lines by scratching lightly with a scratch awl. Imbed
this fob in pitch, either in a pitch bowl or in a small quantity of
pitch placed on a piece of board clamped to the bench or table. Using
an engraving tool, remove the copper from the spot to be enamelled to
the depth of 1/32 of an inch. It is well to have the bottom of the spot
reasonably level but not necessarily smooth and the sides slightly
undercut. Before applying the flux, clean, by pouring a small quantity
of concentrated nitric acid over the cut and immediately rinsing it off
under the water tap. Flux should be kept in a closed jar under water
after grinding, and taken out as needed on the tip of a small strip of
copper previously cleaned with acid. Enough flux should be applied to
cover the bottom of the spot to be enamelled; but the depth of the spot
must not be filled up.
[Illustration: Design for a watch fob]
Now place the fob on a piece of wire gauze on an iron tripod, and apply
the flame of the blowpipe to the under side. Heat very slowly until all
the water is driven off, then force the heat until the flux is fused.
Allow it to cool slowly, then remove any flux that may have adhered to
the surface of the fob by grinding with Scotch stone. Clean with acid
as before, fill the spot with enamel in the same manner as the flux was
applied, and fuse again. After fusing, the surface should be stoned
again to remove inequalities and again fused, cleaned with water and
buffed on the wheel.
If it is desired to apply enamel to sterling silver the flux may be
omitted and the enamel applied directly, but the silver should be
cleaned with sulphuric acid instead of nitric acid, and great care
should be used in heating as the fusing point of silver is but little
above that of enamel. The depth of the engraving on the silver need not
be as great as on the copper.