To avoid peeling and blistering, the paint should be mixed with raw
linseed oil in such proportions that it neither becomes too brittle
nor too soft when dry. Priming paint with nearly all oil and hardly
any pigment is the foundation of many evils in painting; it leaves too
much free oil in the paint, forming a soft undercoat. For durable
painting, paint should be mixed with as much of a base pigment as it
can possibly be spread with a brush, giving a thin coat and forming a
chemical combination called soap. To avoid an excess of oil, the
following coats need turpentine to insure the same proportion of oil
and pigment. As proof of this, prime a piece of wood and a piece of
iron with the same paint; when the wood takes up part of the oil from
the paint and leaves the rest in proportion to harden well, where at
the same time the paint on iron remains soft. To be more lucid, it
need be explained, linseed oil boiled has lost its oleic acid and
glycerine ether, which form with the bases of pigments the insoluble
soap, as well as its albumen, which in boiling is thrown out. It
coagulates at 160° F. heat; each is needed to better withstand the
action of wind and weather, preventing the dust from attaching itself
to a painted surface, a channel for ammonia in damp weather to
dissolve and wash off the paint. In later years linseed oil has been
extracted from linseed meal by the aid of naphtha and percolation, the
product of a very clear, quick drying oil, but lacking in its binding
quality, no doubt caused by the naphtha dissolving the fatty matter
only, leaving the glycerine and albumen in the meal.

All pigments of paint group according to their affinity to raw linseed
oil into three classes. First, those that form chemical combinations,
called soap. This kind is the most durable, is used for priming
purposes, and consists of lead, zinc, and iron bases, of which red