6 PAINTING MATERIALS
the resulting wax will thus be largely adulterated. Besides its use in the arts (see
Waxes, history in painting), and it has doubtless been the principal wax used^by
painters, beeswax is mainly used in candle manufacture and in the preparation
of wax polishes.
Benzoin (see also Resins) is a dark, resinous substance obtained from trees
(Styrax Benzoin and other species) growing in Siam and in Sumatra. Siamese
benzoin has a characteristic odor which results partly from the presence of I per
cent vanillin. It has frequently been used as a plasticizer for varnishes and lac-
quers. It was imported into Europe at an early period, but Merrifield (I, cclx)
says that it does not appear to have been used as an ingredient in varnish until
the middle of the XVI century when it became a spirit varnish, but did not figure
in the preparation of oil varnishes. It is mentioned in various mediaeval MSS.
Binding Medium (see Medium).
Bitumen Waxes form a link between the vegetable waxes and the mineral
waxes. In this respect they resemble lignite and peat, the parent substances which
are bodies intermediate between vegetable and mineral in character (see also
Waxes and Montan Wax).
Blown Oil. The usual procedure for preparing blown oil is to pass an air
current through the oil (see Oils and Fats), at about 120° C., in the presence of
traces of cobalt driers. Blown linseed oil is used somewhat instead of stand or
polymerized oils which are more expensive to manufacture. By prolonged blow-
ing, drying oils yield jelly-like or even solid, elastic masses. Fatty oils belonging
to the class of semi-drying oils lend themselves especially to the manufacture
of blown oils. Rape oil and cotton-seed oil* are blown in order that the products
may be mixed with mineral oils to produce specific lubricants, while other blown
oils find various technical applications.
Boiled Oil is oil which has been heated with the addition of lead, manganese,
or cobalt oxides, or other suitable compounds of these elements, such as the
linoleates or resinates. Formerly it was usual to heat the oil at 2,60° to 290° C.,
to add a metallic oxide, and to continue heating for a few hours until a homo-
geneous solution was obtained. The modern practice is to operate at lower tem-
peratures (130° to 150° C.) and to employ c soluble driers' such as the metallic
resinates or linoleates. If the oil is blown with air, the driers may be incorporated
at temperatures as low as 100° C,, for slight oxidation of the oil facilitates dis-
persion of the driers. These are probably colloidally dispersed, not truly dissolved.
Boiled oils have the property of absorbing oxygen from the air at a much more
rapid rate than does raw linseed oil, and the time required for the formation of
a skin is thereby much shortened (see Oils, drying process). They are used largely
for industrial paints, varnishes, and enamels, and for waterproofing, for electrical
insulation, and for patent leather. Doerner (pp. 105-106) says that commercial
boiled oil is not of much use for artistic purposes because it dries with a sleek,
greasy sheen and easily forms a skin.