Purple being a secondary colour, composed of blue and red, it follows of course that any blue and red pigments, which are not chemically at variance, may be used in producing mixed purple pigments of any required hue, either by compounding or grinding them together ready for use, or by combining them in the various modes of operation in painting. In such compounding, the more perfect the original colours are, the better in general will be the purple produced. In these ways ultramarine and the rote colours of madder constitute excellent and beautiful purples, which are equally permanent in water and oil, in glazing, or in tint, whether under the influence of the oxygenous or the hydrogenous principles of light and impure air, by which colours are subject to change. The blue and red of cobalt and madder afford also good purples. Some of the finest and most delicate purples in antient paintings appear to have been similarly compounded of ultramarine and vermilion, which constitute tints equally permanent, but less transparent than the above. Facility of use, and other advantages, are obtained at too great a sacrifice by the employment of perishable mixtures, such as are the carmines and lakes of cochineal with indigo and other blue colours.