Linseed, poppy, and nut oils are the fixed oils used as vehicles; turpentine and occasionally spike-lavender are the essential oils so used. Of the fixed oils, linseed is in most common use. It should be of a pale amber colour, transparent, and limpid; and, when used in moderately warm weather, it should dry in a day. The most valuable qualities of linseed oil, as a vehicle, consist in its great strength and flexibility. It is by far the strongest oil, and the one which dries best and firmest under proper management. The next in importance is poppy oil. It is inferior in strength, tenacity, and drying, to linseed oil; but it has the reputation of keeping its colour better than linseed oil; and it is on this account generally employed in grinding white, and most of the light pigments. Nut oil is more uncertain in its qualities than either linseed or poppy oil; and is frequently extremely long in drying. Poppy oil, however, supplies its place so well, that it is not commonly required. Oils are all more or less influenced in their drying by the colours with which they are combined; some of which greatly accelerate, while others retard it.
With certain colours some oils will scarcely dry at all, unless means are employed to cause them to do so.