26. Yellow, bearing, as already stated, the same relation to light as blue does to shadow, is capable of reduction, through several shades, till it merges into a cream white, its color limit.

27. Naples yellow is composed of the salts of lead and antimony, owing its name to the fact that it is supposed to have been first obtained from a volcanic product of Mount Vesuvius, near Naples. It is a very opaque pigment, and, therefore, covers thoroughly the surface to which it is applied, but is not as brilliant as chrome yellow and is very difficult to grind.

28. Chrome yellow, one of the most durable of pigments, is obtained from the subchromate of lead. Frequently adulterated with gypsum, it is prepared by mixing diluted solutions of acetate or nitrate of lead and bichromate of potash.

29. King's yellow is the name of a very dangerous and unsatisfactory pigment obtained from arsenic. It is not very poisonous, but injurious to other colors when mixed with them. Least durable of all the yellow pigments, it is known, also, under the names of yellow orpiment and Chinese yellow.

30. Yellow ocher is a natural clay, colored by oxide of iron, found abundantly in many parts of England. Stone ocher is a similar pigment, found in the form of balls embedded in the stone of the Cotswold Hills, England. It varies in tint from yellow to brown.