then highly polished, or covered with crystal varnish.
b. The inside of the socket in which the stone or paste is to be set is covered with tin foil, by means of a little stiff gum or size; when dry, the surface is polished and the socket heated, and whilst it is warm, filled with quicksilver; after repose for two or three minutes the fluid metal is poured out, and the stone gently fitted in its place; lastly, the work is well fitted round the stone, to prevent the alloy being shaken out.
c. The bottom of the stone is coated with a film of real silver, by precipitating it from a solution of the nitrate in spirit of ammonia, by means of the oils of cassia and cloves.[318] This method vastly increases the brilliancy both of real and factitious gems, and the work is very permanent.
[318] See Silvering.
2. (Coloured foils.) The following formulæ produce beautiful coloured effects, when judiciously employed:—
a. (Amethyst.) Lake and Prussian blue, finely ground in pale drying oil.
b. (Blue.) Prussian blue (preferably Turnbull’s), ground with pale, quick-drying oil. Used to deepen the colour of sapphires.
c. (Eagle marine.) Verdigris tempered in shell-lac varnish (alcoholic), with a little Prussian blue.
d. (Garnet.) Dragon’s blood dissolved in rectified spirit of wine.
e. (Vinegar garnet.) Orange lake finely tempered with shell-lac varnish.