Ultramarine (Artificial).
—This is one of the chief blues used by the painters, and must be bought ready made. It cannot be imitated, but it can be bought in many different qualities. It must not be mixed with chromes or white lead, as it contains sulphur, and there would on that account be a likelihood of discolouration. Natural ultramarine is very expensive.
CHAPTER VII.
Yellows.
A great variety of yellows may be obtained by using the different shades of yellow chrome, etc., on the market, adding a little red occasionally. It may be taken as a general rule that blacks should not be added to yellow unless a greenish tint is desired. If a yellow is too bright it may be lowered by adding a small quantity of blue and red. Instructions for obtaining the various grades of yellow are given explicitly below.