When the stoning is finished it will be found that the surface of the enamel presents a rather dull or dead appearance, which will be removed by again firing the piece. Before this firing, however, the piece should be submerged for about a minute or less in hydrofluoric acid and then brushed in clean water. This may be done with any small stiff-bristled hand brush. The piece will dry readily in the air, but more quickly if first dipped in scalding hot water or brought in contact with steam. It may also be dried in hot air or sawdust. When dry it is ready to be fired.
Sometimes after stoning, low places or pit-holes are found in the enamel surface, which may be remedied by re-charging these places with enamel and then firing the piece.
When only a very small amount of enamel is to be stoned off, or when one does not want to fire the piece after the stoning, a soft soapstone called a “Scotch stone” may be used to advantage.
If the piece to be stoned is small it is desirable to have a small wooden stick the size of a pencil with which to hold the piece steady and keep it from slipping out of its mold. Of course a mold is not always necessary, but will often be found very convenient.
A sharp steel tool, such as a three-cornered scraper or a slightly dull awl, is very useful to clean out pit-holes or to chip enamel off from places where it is not desired.
When a large number of pieces are to be stoned, it is advantageous to use an emery or carborundum wheel of No. 90 to No. 120 grit, from two and one-half to six inches in diameter and from three-eighths to three-fourths of an inch thick, revolving on a lathe at a low rate of speed. A stream of water should be kept constantly dropping on the wheel in order to keep both the wheel and the work wet.
Rubber cots are a great protection to the fingers, which are gradually worn away by the stones.
CHAPTER VI
POLISHING
After an enameled piece has been stoned and fired for the last time, it is often desirable to give the enamel a gloss or polish additional to that which it naturally receives from the firing.