Ochres.
—Analysis is of no value in determining the value of an ochre. Sometimes chrome yellow is used to tone it up. The colour is an important feature, as is also the fineness.
Blacks.
There are a number of blacks on the market, drop black, ivory black, blue black, vegetable black, carbon black, etc. The subject of their tests is a somewhat intricate one, but its tinting strength can be readily ascertained by mixing with white lead or zinc in the manner already described. They are frequently adulterated with barytes.
Blues.
Prussian blue is one of the most important used by the painter. It is very strong and a little goes a long way. It must be very finely ground or it is likely to settle out. A pure Prussian blue has a rich bronze appearance when looked at from certain points of view. The tint made by mixing with white should be clear and free from any leaden or gray appearance. Some Prussian blues have a certain red or purplish cast which cannot be removed. These should be avoided, as if a purple is required it is a simple matter to add a little red to the blue to produce the desired colour. As shown in our samples of paint, one part in a hundred of good Prussian blue gives a distinct sky blue.
Ultramarine.
—As explained elsewhere, this colour cannot be mixed with white lead. Where it is necessary to make a tint, zinc white should be employed in preference.
Umbers and Siennas.
The colour should be a rich brown rather than a red cast. In siennas prepared for grainers’ use, it is important that they be transparent rather than opaque. Richness and quality of tint should be considered rather than the body.