Scientific American Supplement, No. 443, June 28, 1884 | Page 4

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 lead takes up the
most oil; next, white lead, the pure carbonate Dutch process made,
following with zinc white and iron carbonates, as iron ore paint, Turkey
umber, yellow ocher; also faintly the chromates of lead--chrome-green
and chrome-yellow, finishing with the poorest of all, modern white lead,
made by the wet or vinegar process. The second class being neutrals
have no chemical affinity to linseed oil; they need a large quantity of
drier to harden the paint, and include all blacks, vermilion, Prussian,
Paris, and Chinese blue, also terra di Sienna, Vandyke brown, Paris
green, verdigris, ultramarine, genuine carmine, and madderlake. The
last seven are, on account of their transparency, better adapted for
varnish mixtures--glazing. The third class of pigments act destructively
to linseed oil; they having an acid base (mostly tin salt, hydrochloride
of tin, and redwood dye), form with the gelatinous matter of the oil a
jelly that will neither work well under the brush nor harden sufficiently,
and can be used in varnish for glazing only; they are not permanent in
color, and among the most troublesome are the lower grades of
so-called carmines, madderlakes, rose pinks, etc., which contain more
or less acidous dyes, forming a soft paint with linseed oil that once dry
on a job can be twisted or peeled off like the skin of a ripe peach. All
these combinations of paint have to be closely observed by the painter
to insure his success.
Twenty-five years ago a house needed to be painted outside but once in
from five to seven years; it looked well all the time, as no dust settled
in the paint to make it unsightly. Painters then used the
Dutch-process-made white-lead, a base and raw linseed oil, a fat acid,
which formed the insoluble soap. They also put turpentine in the
following coats, to keep up the proportions of oil and pigment. All held
out well against wind and weather. Now they use the wet-process-made
white lead, neutralized by vinegar, with oil neutralized by boiling, from
the first to the last coat, and--fail in making their work permanent.
W.S., in the Building News, relates an unaccountable mysterious
blistering in a leaky house, where the rainwater came from above on a

painted wood wall, blistering the paint in streaks and filled at the lower
ends with water, which no doubt was caused by the water soaking the
wood at the upper ends where there was no paint, and following it
down through the fibers, pushed and peeled off the soft, inadhesive
paint. Green, sappy, and resinous wood is unfit for durable painting,
and to avoid blistering and peeling wood should be well seasoned and
primed with all raw linseed oil, some drier, to insure a moderately slow
drying, and as much of a base pigment as the painter can possibly
spread (much drier takes up too much oil acid, needed for the pigment
base to combine with), which insures a tough paint that never fails to
stand against blistering or peeling, as well as wind, weather, and
ammonia.
The coach, car, and house painter can materially improve his