Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/245

Rh from good and full-grown seeds should, when held up to the light, appear clear, pale and bright; it is sweet to the taste and has little or no smell.

Linseed oil may be purified by the following process: Place the oil in a bottle or jar, and drop into it some powdered whiting, stir or shake up the mixture and allow it to stand on the stove, or in an oven, not too hot; the whiting will very soon carry down all color and impurity and form a precipitate at the bottom. The refined oil at the top may then be poured off.

In rare instances, where the least yellowness in the oil would be injurious, nut or poppy oil may be used with advantage; but, as already stated, linseed is the oil used for general purposes.

Oils of a nature suitable for painting are the most commodious and advantageous vehicle to colors hitherto discovered, first, because the unctuous consistence of them renders their being spread and layed on a surface with more evenness and expedition than any other kind of vehicle; secondly, because, when dry, they leave a strong gluten or tenacious body that holds the colors together, and defends them much more from the injuries either of the air or accidental violence than the vehicles formed of water. The principal and most general quality to be required in oils is their drying well, which, though it may be assisted by additions, is yet to be desired in the oil itself, as the effects of the pigments used in it are sometimes such as counteract the strongest driers, and occasion great delay and trouble from the work remaining wet for a great length of time, and frequently never becoming thoroughly hard. There are some oils that have this fault to an incurable degree. The next quality in oils is the limpidness, or approach to a colorless state, which is likewise very material; for where they partake of a brown or yellow color, such brown or yellow necessarily mixes itself with the pigments; but, besides the brown color which may be visible in the oil