PAINTING MATERIALS
4
It has been suggested (' Methacrylate Resins/ p. 1163) that the monomeric
ester, since it has such low viscosity and can be polymerized so easily, may be
used as an impregnating agent which can be polymerized in situ. Porous, fibrous,
and cellular materials, which are ordinarily difficult to impregnate because of
the viscosity of the organic solutions of the polymers, may be treated for pro-
tection and stiffening in this way. It is also reported (ibid.} that * monomeric
methyl methacrylate has been used to protect wood to give a final product con-
taining as much as 60 per cent by weight of resin/
Albumen (see Egg White).
Alkyd Resins (see also Synthetic Resins). The alkyd resins are obtained by
the elimination of water from polyhydric alcohols (glycol and glycerol) with
dibasic acids (phthalic, etc.). These resins have been prepared from a number of
different ingredients leading to widely differing properties. There are many so-
called ' alkyd resins.' Combined with drying oils, they are now much used in the
industrial preparation of paints, lacquers, and enamels which are durable and
flexible and do not yellow. Some of the resins are thermosetting and are used for
making molded articles. The alkyd resins are the most important of the synthetic
resins in the industrial paint and lacquer field today. Incorporation of alkyd resins
in cellulose nitrate and cellulose ester coatings has helped to overcome some of
the disadvantages of the latter.
Amber (see also Resins). The name ' amber ' in early times was given to many
hard resins. It is, properly, a fossil resin found chiefly on the shores of the Baltic
Sea but also in Denmark, Sweden, Norway, France, and along the coast of
England. A dark variety has been found near Catania, Sicily. Aristotle was the
first to record that amber was not a mineral but a fossil tree resin. It is mostly
known in its natural state as jewelry. Beads of it have been found in early English
graves and good specimens are still highly valued for ornamental purposes. It
has been used, also, as a varnish ingredient, undoubtedly when adulterated with
other hard resins.
The chief distinguishing feature of true amber is its yield of succinic acid
when heated, and the name, ' succinite,' is now commonly used in scientific
writings to denote the real Prussian amber. There are several ways to distinguish
between amber and copal with which it is often confused or adulterated. One is
the presence of succinic acid in the distillate of amber; another is the insolubility
of amber in cajuput oil which completely dissolves copal; amber, when heated
quickly, splits up and then fuses into a viscous liquid, the drops of which rebound
when falling on a cold surface; copal resin does not have this characteristic.
Amber is practically insoluble in ordinary resin solvents. When made into a
varnish, it is melted or distilled and the residue is dissolved in amber oil, oil of
turpentine, or a fatty oil. It makes a very dark, slow-drying varnish, unsuitable
for paintings, and there is doubt that it was ever employed alone for this purpose,
Animal Waxes (see also Waxes and Vegetable Waxes). These are obtained
from a great variety of sources and have little in common, except their absence
of glycendes. Small deposits may be found in many parts of animals and are