OILS AND DRIERS.
Linseed oil is produced by expression from the seeds, either by hydraulic or steam power. This material varies in quality: According to the goodness of the seed from which it is expressed, and according to its age and clearness; for, when a large stock is kept, it is found that, in about six months, there is a considerable amount of accumulation of refuse at the bottom of the tank, which is only fit to be employed in mixing coarse paint for out-door work. The best is yellow, transparent, comparatively sweet-scented and has a flavor resembling that of the cucumber. Great consequence has been attributed to the cold drawing of this oil, but it is of little or no importance whether moderate heat be employed or not in expressing it. Several methods have been contrived for bleaching and purifying this oil so as to render it perfectly colorless and limpid, but these give it more beauty to the eye, in a liquid state, without giving it any permanent advantage, since there is not any known process for preventing the discoloring after its drying, and it is, perhaps, better upon the whole that this and every vehicle should possess that color at the time of using to which it subsequently tends, so that the painter may depend on the continuance of his tints, and avoid the disappointment and annoyance arising from a change of color.
Linseed oil is sometimes boiled with litharge to make it dry quickly, but when it is thus treated it is unfit for best work.
The quality of linseed oil may be determined in the following manner: Fill a phial with oil and hold it up to the light; if bad, it will appear opaque and turbid, its taste will be acid and its smell rancid. The oil which is expressed
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