Enamel is a glass fused to the surface of metals, for decorative
purposes. It is bought in flat discs about 1/4 in. thick and weighing
from 5 to 6 ounces. These discs are broken up so that one is able to
buy enamel in small quantities. It comes in any colour and when put
upon the surface correctly the colour does not change and it is not
affected afterward by atmospheric influences.
_Tools:_ One needs few tools for this work. A wooden mallet, a mortar
and pestle, and a small spoon used to put the enamel on the metal when
filling the design will be found sufficient. The spoon may be made by
taking a 1/8-in. piece of silver or copper wire with about 1/2 in. of
the end flattened down spoon shaped. File this end round and smooth so
there will be no ragged edges.
_Process:_ When you have decided upon the colour which you wish, put as
much enamel as you will need into the mortar and cover it with clear
water. The water washes the enamel and prevents it from flying out
as it is broken up. Place the pestle on the pieces of enamel and tap
gently upon the end of the pestle with the wooden mallet, till the
enamel is broken up into fine pieces. While doing this the water will
become discoloured. Drain the water off and pour fresh water on. Repeat
this so long as the water becomes discoloured. With the pestle grind
the enamel to a fine paste. Press down upon the pestle, at the same
time give it a twisting movement with the wrist. When the water remains
clear and the enamel is pasty and free from lumps it is ready for use.
While using it keep it just covered with clear water. This prevents its
drying and in this dampened state it is in the best working condition.
_How to place the enamel on the metal:_ With the small spoon pick the
enamel up out of the mortar, place it on the metal and press it down
into any depression. Keep it well moistened all the time. Repeat this
until the whole depression is covered. If any part is left uncovered,
that part will show black after firing. Then each black spot must be
scraped clean, covered with enamel again and refired, which makes
much unnecessary work, so be careful at the first to place the enamel
just where it should be on the metal, and so avoid the extra work and
firing. _The muffle furnace:_ This is a small furnace made for the
purpose of melting enamels by what is called a reflected heat. The
muffle is a half rounded, shaped clay form open only at one end, into
which the piece to be fired is put. The flame of the furnace plays on
the outside of this muffle. The temperature is raised to the required
heat and the piece inside the muffle is fired without having any flame
playing directly upon it. The reflected heat does the work. These
furnaces can be bought in almost any general supply store. They come
in all sizes. Natural or artificial gas can be used for heating; the
regular hose or tube attachment is all that is necessary.
_The piece in place for firing:_ It is usually best to light the oven
before you begin to place the enamel on the work to be fired. The
furnace heats up in the meantime. Place the piece on the top ledge
of the furnace close to the chimney. This is a good place to dry the
moisture out of the enamel. If this is not done the steam generated by
the moisture and the heat causes explosions, which in turn disturb the
enamel surface and dislodge small particles of the enamel. When the
steam has stopped rising from the enamel--which you can tell by holding
the piece between you and the light--the moisture has dried out and the
work can be put into the muffle by use of a long pair of muffle tongs.
Extreme care must be taken when placing the piece to be fired into the
furnace. The enamel is now very dry. The particles are no longer held
together by the moisture and the least jar will dislodge them. The
doors of the furnace are usually in two pieces, so that the upper half
can be lifted away from time to time. One can look in and watch the
process of melting. When the enamel is first put into the furnace and
the heat begins to melt it, it rapidly changes colour. As it begins to
melt it settles down and takes on a glassy, soft, smooth surface. At
this point it is ready to take out. It is placed again on the top of
this furnace, where it cools off slowly, otherwise the difference in
expansion between the metal and the glass would cause the surface to
crack. After one or two trials one easily recognizes the critical time
when the enamel is well baked. These directions are only for enamelling
flat surfaces. If one should wish to enamel both the inside and outside
of a box lid rounded on the top and curved on the under side, a few
large drops of gum arabic should be mixed with the enamel used for the
under side. This prevents it from dropping off when in position for
firing.
When the work has cooled off so that it can be handled, it will show a
surface every part of which is covered, if carefully done. If not the
black spots will appear. These are copper spots oxidized by the heat,
and must be thoroughly scrubbed and scraped. The enamel edges around
these spots must be scraped away, covered with enamel, and refired.
If there are no spots shown, the work is ready for finishing. You will
find on the upper edge of the enamel line a black line caused by the
impurities in the enamel which rise to the top edge. Scrape this off
with a fine file until it entirely disappears.
The copper, too, usually takes on beautiful colours during the heating
process. Many like to leave the colours just as they happen to come
by the heat, others prefer to polish the surface to bring out the
real copper colours rather than the oxide colours. To clean the oxide
off one must put the piece into a pickling bath made up of one part
of sulphuric acid to eight parts of water. This softens the scum on
the surface of the metal so that a soft rag dipped into any cleaning
material like pumice stone will easily clean it off.