The Permanence of Colours.
—It must be admitted that it is very disappointing to a painter to find, after taking pains to produce the exact colour required, that it flies or fades after a little exposure to the weather. The tests for the permanence of a colour when exposed to light are simple enough and are to mix a little of the colours to be tested in oil and to spread them on different slips of paper, cut the paper in half, number each half with corresponding figures or letters, expose one half to a strong light for as long as may be deemed desirable and put the other half away into a safe place where the light does not penetrate. Waxed paper is the best, as it will not absorb the thinners or, better still, glass may be used, this being cut across with a diamond after the paint has been applied. It need hardly be said that the permanence of water colours is entirely different from that of oil colours. Some very useful experiments were made several years ago by Capt. Abney on the permanence of water colours, and these were published in the form of a blue book. As far as pigments are concerned, we consider that yellow ochres, siennas, umber, Vandyke brown, and the earth colours generally are permanent, as are Venetian red, Indian red, chrome yellow, and lemon yellow. Ultramarine, Prussian blue and vermilion are also permanent or nearly so.
We may now take each colour separately following the order taken by the late Mr. W. C. Wilson, who arranged the above quoted table in conjunction with the author.