To produce embossed letters, or figures on marble.—Take some of the coloured varnish described at 37, and with a hair pencil, draw the letters, on the marble, (which should be previously well polished,) and also cover with the varnish, every part of the face of the marble that is to remain plain.
Lay the marble in a horizontal position and make a border of oil putty round it, and pour on muriatic acid to the depth of half an inch on the marble.
When ebulition ceases, the acid may be drained off, and the work examined; and if the letters are not sufficiently prominent, a fresh quantity of the acid may be added. When the work has been thus corroded to the depth required, the varnish may be washed off with spirits of turpentine. The acid that has been thus employed need not be lost, for a muriate of lime being thus formed, may be crystallized by a slight evaporation, and preserved for other purposes; or by the addition of a small quantity of sulphuric acid a sulphate of lime is precipitated, and the muriatic may be poured off and be used again for the same or a similar purpose.