PAINTING MATERIALS
varnishes is about like that of ethyl alcohol. It is a good solvent for cellulose ace-
tate. Toch says (p. 91) that diacetone alcohol is one of the most important restor-
ing agents for paintings because of its miscibility with other solvents, its slow
evaporation, and its ability to coalesce the crackle on old varnish films.
Dibutyl Phthalate (CJELJ^COOCJJ.^) is the most widely used chemical
plasticizer for commercial lacquers. A colorless liquid, it has a boiling point be-
tween 200° and 2i6°C. and a flash point of i6o°C. It is made by the direct action
of butyl alcohol on phthalic anhydride and has a high degree of stability, being
only very slightly volatile. Amounts equalling or exceeding the solids content are
used in compounding commercial lacquers. Although the films that contain it
remain plastic for a long time, they eventually lose it, with a consequent harden-
ing. Gardner (p. 419) reports experiments in which it was found that a film of 2
parts nitrocellulose and I part dibutyl phthalate lost only 0.98 per cent of the
plasticizer after baking for 20 hours at 5o°C. It is light-stable but yellows very
slightly on long standing. On a number of resins, including mastic, it has some
solvent action. Other alkyl esters of phthalic acid are used as plasticizers—diethyl
phthalate, diamyl phthalate, and dimethyl glycol phthalate.
1,2-Dichlorethane (see Ethylene Bichloride).
Diluent. In its broad meaning this is any material added to a paint or varnish
to make it thin and easily applied. More specifically with respect to varnishes
and lacquers, it is an added liquid which by itself would not serve as a solvent for
the film material. As such, it can be put into the mixture only to a limited extent
without causing precipitation of the solid. The amount of diluent that is tolerated
in combinations of film materials and solvents is called * the dilution ratio.' No
film material can be properly called a ' diluent.' Whether or not a completely vola-
tile fluid is a diluent or a solvent depends entirely on its relation to a particular
solid. If the fluid is capable of dispersing all or part of that solid and holding it as so
much suspended matter, then that fluid is a solvent for that solid. If it can not do
this but is in some degree miscible with a solution formed by another fluid, it is
a diluent. Turpentine, for example, is a solvent for mastic resin but is only a
diluent to a small extent for solutions of certain synthetic resins. Petroleum
naphtha is a solvent for dammar resin but is only a diluent within limited pro-
portions for solutions of mastic.
Dioxane (i,4-dioxane [O : (CH2CH2)2 : O]) is a cyclic diether. The boiling
point is ioi.5°C. and the liquid is colorless and stable, with a faint ethereal odor.
It is made by distilling ethylene glycol with sulphuric acid. Completely miscible
with water and with most organic solvents, it has itself a high solvent strength
for natural and synthetic resins, and also for oils, fats, and waxes. Like ether, it
is much used in the extraction of ethereal oils, but since it has a relatively low
volatility, it is much more useful in the removal of old surface films, especially
those in which a wax or partly dried oil is present. The vapors are explosive, and