PREPARATION OF THE METALS
MANY metals can be enameled, but the most practical ones, those most
used in jewelry, are gold, silver, copper, and their alloys. Hence we
will confine our descriptions to these metals.
Whatever metal is used, however, must first be made chemically clean
before it is “charged” or covered with enamel. This may be done in a
number of different ways, of which the following is considered the most
practical.
The metal, whether gold, silver, or copper, must be annealed by being
heated to a red heat and allowed to cool slowly in the air. When cool it
will be found to be covered with a black oxide.
The metal must now be plunged for half a minute or more into a solution
called a “dip,” consisting of two parts sulphuric acid (H_{2}SO_{4}),
two parts nitric acid (HNO_{3}), and a slight touch of hydrochloric acid
(HCl); a few drops of the latter to the gallon will suffice. This dip
will clean the surface of the metal and make it bright. As the solution
gets old it will become weak and a longer dip will be required. The
ordinary commercial acids are suitable for making these dips. Care
should be taken not to inhale the fumes of the acids, as they are quite
poisonous.
This dip may be used cold, but better results are obtained when it is
heated to 170°F. A convenient way to heat it is to set the jar
containing the dip in a larger jar containing water and then to heat the
water in the larger jar.
Many prefer to use first a hot and then a cold dip, rinsing the metal in
clean water between the dips. Experience will soon teach one to tell
when the metal is clean by looking at it, and this in fact is the only
satisfactory way, as the length of time required will vary with the
condition of the metals and the strength of the dip.
[Illustration:
FIG. 3. ENAMELER’S SPATULA WITH WOODEN HANDLE.
]
After the dip the metal must be thoroughly rinsed in clean water and
then dried in clean sawdust or hot air. If rinsed in very hot water the
metal will dry itself almost immediately. Some prefer to rinse the metal
in ammonia as well as in water in order to rid it of all trace of the
acid, but this is not generally necessary. If the metal is copper or
gold it is now ready to be charged, but if it is silver it must be
“fire-stained.”
There are many other possible ways of cleaning metals, but the above
means are generally used and will doubtless be found the most
convenient. If small quantities only are being “cleaned,” a copper
pickle pan and a Bunsen gas burner will suffice, while for large
quantities earthen pickle pots and large jars will be found
advantageous. Metals if “wriggled,” that is, scraped or engraved all
over with a graver, are generally clean enough to be charged.
If silver is used it must be “fire-stained,” or have the “fire” taken
out of it. This is done in the following manner. The silver is submerged
for a minute or more in a solution of four parts nitric acid and one
part water, heated to 170°F. The acid will react on the silver, which
will become covered with a brownish scum. The silver should now be
rinsed in clean water and brushed with a metal brush in a solution of
soap-tree bark and water. This will clean the scum off the silver and
make the latter bright. After being rinsed in clean water, the silver is
ready to be charged with enamel. Sour beer, or a solution of licorice
root and water may be used instead of soap-tree bark. It will be very
convenient to have the metal wire brush a circular one revolving on a
lathe.
If red enamel is to be used, the metal should always be either wriggled
or engine turned or else have some design cut sharply in it, in order to
bring out the brilliancy of the color. Engine turning and sharp
engraving or relief in the metal background will always enhance the
brilliancy and give an additional sheen to any transparent colors. As
the depth of the enamel layer has a great deal to do with the shade of
the enamel, different effects can be obtained, even when only one enamel
is used, if the metal background has been cut lower in some places than
in others.
If the silver is not “fire-stained,” red enamel will often become maroon
when fired, and fondant and other delicate colors will become streaked
or spotted. If the fire-staining and dipping have not been carefully
done, the enamel is likely to chip out, have pit-holes in it, or contain
black blotches.
As the acid fumes eat the flesh quite rapidly, it is advisable to wear
rubber gloves when dipping the metals.
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