In closing this chapter it may be useful to state that the pigments to which a place in our Class I. has been assigned have stood the very severe test of long exposure to direct sunlight. On a subsequent page it will be shown that this method of determining the stability of pigments is not in all cases a fair one, because changes brought about by such exposure may not occur at all when the temperature does not rise beyond a particular point, and when the radiant energy of light and actinism does not exceed a moderate measure of intensity. So far, then, as exposure to light is concerned, it may happen that some of the pigments in Class II. really deserve a higher position than that assigned to them in our table. In this connexion we may give some of the conclusions which Messrs. Winsor and Newton have published as to the stability of oil colours when exposed, not to sunshine, but to a strong north light. It will be noticed that the class of permanent pigments has been greatly enlarged as the result of the milder ordeal through which the materials have passed:

Class I. - Permanent

Zinc white. Aureolin. Cadmium yellow. Yellow ochre. Raw sienna. Baryta yellow. Mars yellow. Vermilion. Venetian red. Light red. Indian red. Alizarin lakes. Crimson madder.

Madder carmine. Pink madder. Rose madder. Purple madder. Brown madder. Rubens' madder. Scarlet lake (new). Burnt lake (madder). Cobalt green. Oxide of chromium. Viridian. Cerulean blue. Cobalt blue.

Ultramarine. Manganese violet. Cobalt violet. Prussian brown. Caledonian brown. Cappagh brown. Burnt umber. Burnt sienna. Vandyke brown. Bone brown. Black lead, Blue black. Ivory black.

Class II. - Moderately Permanent

Flake white. Chrome yellow. Naples yellow (imitative). Kings' yellow.

Indian yellow. Green cinnabar. Emerald green. Malachite. Rose dorée.

Leitch's blue. Prussian blue. Antwerp blue. Asphaltum. Brown pink.

Class III. - Fugitive

Citron yellow

(ZnCrO4). Yellow lake. Gamboge. Primrose yellow. Carmine.

Burnt carmine. Crimson lake. Indian lake. Purple lake. Violet carmine.

Green lake. Sap green. Verdigris. Indigo. Italian pink.