The third is the change produced by artificial means, from exposing the oil a long time to the sun, whereby it is freed from its grosser and more feculent parts, and rendered colorless, and of a more thick and less fluid consistence than can be produced by any other treatment; but, at the same time, it is made less likely to dry, particularly when used with mineral colors, as vermilion, Prussian blue and King's yellow; it likewise becomes disqualified by other bad qualities that render it of little use as a vehicle for painting. Oils in this state are called also fat oils, though it is a change that has not the least affinity with either of the other, but, on the contrary, differs from both. In speaking, therefore, of the fattening of oils or colors, attention should be had to the not confounding these three several kinds one with the other.
Linseed oil, from its cheapness, is the only oil in common use for house painting, and it may, by proper management, be made to answer for every kind of work. This oil is pressed from the seed of flax, and is best when manufactured in great quantities. The general defect in linseed oil is its brown color, and its tardiness in drying, both of which are in a much greater degree found in some parcels than others. There is also found such as, in consequence of its being mixed with the oil of some other vegetable accidentally growing near it, partakes of the nature of olive-oil, and cannot be made to dry by any means whatever. The faults of the color and want of drying quality may be greatly reduced, if not entirely taken away, by keeping the oil for a length of time before it is used; it then becomes fat in the second sense of the word, as before explained, and is a good vehicle for color without any mixture; but it is generally used with a proper drier, as it never by itself becomes sufficiently pure to use with white or other light tints, without imparting a brown color to them.
Poppy Oil. This is a colorless oil, and is in some in-
