Chemistry has, however, been called into operation, and, by various processes, oil can be rendered siccative in a very short time, and so enables us to make use of it in the manufacture of varnish.
Linseed oil is not soluble in water, very slightly in alcohol, but can be dissolved in ether and essential oils.
If prepared by the cold process it is a light yellow colour, and if prepared by heat it is brown yellow.
In common oil, there is often a solution of oils of resin, and such oils must never be employed if good results are to be obtained.
The quality of oil depends completely on the nature of the seed from which it is extracted.
A good oil is very liquid and transparent, and is practically odourless.
Viscous and strong smelling oils are the result of using seeds of inferior quality, or those not fully matured.
Oils as usually obtained in the trade are seldom pure, they generally contain colouring matter, and are otherwise adulterated, therefore only those of the very best quality must be used.
