Embossing on glass is usually done by means of hydrofluoric acid. The design is pounced or sketched on with French chalk. Then every part that is not to be embossed is painted over with a special Brunswick black. A little wall of tallow is then built all around the pane of glass laid flat, and the acid is gently poured on. In about half an hour it has eaten into the glass sufficiently to form a well-defined pattern. The acid is poured off into a guttapercha bottle, the tallow removed, and the surface washed with clean water. The black is softened with turpentine and removed by means of an old chisel.
A priming coat can never prove satisfactory unless it is composed of very fine materials. White lead, red lead, or white lead and ochre are among the best primers.
The best tests of linseed oil for the practical man are the senses of smell and taste. The analysis of linseed oil is a very difficult process, and every oil dealer should educate his senses by constant practice and recognise the pure oil immediately when he smells or tastes it. Adulteration in boiled oil is more difficult to detect than it is in raw oil.
Never mix two different kinds of driers in a paint; they may re-act upon one another and actually retard the drying of the paint.
Too much driers in paint will destroy its durability and may affect the gloss.