If enamel is to be kept for any length of time it should be kept either as chunks preferably or as coarsely ground powder. When coarsely ground it may be kept dry in a dirt-proof jar or bottle.
The “dregs” and “slimes” if washed clean may be kept and used for paints in painting on enamel.
When enamel is bought in the form of a powder it is generally necessary to grind it finer and wash it thoroughly.
CHAPTER II
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 (H2SO4), two parts nitric acid (HNO3), 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.