32 PAINTING MATERIALS
milky liquid which rapidly thickens and darkens on exposure to air. It can be
kept in closed containers without change for a considerable length of time. On
standing, it separates into two layers, the top, of superior quality, being filtered,
slightly heated, and thinned before it is used.
Secrecy surrounded the methods of making and working lacquer, and it is only
recently that its composition and the art of its manufacture and application have
been generally known and studied. When used as a furniture varnish, it can be
applied in extremely thin coats. It has the unique quality of attaining extreme
hardness in the presence of moisture. It does not become brittle, and can be highly
polished. It affords permanent protection as it is unaffected by acids, alkalis,
alcohol, or heat up to about 160° C. It may be dried either in a moist chamber at
temperatures below 20° C., which takes several days, or at 100° to 200° C., which
takes only a few hours. Moisture and temperature are both important. In drying
at low temperatures, evaporation is increased with the amount of moisture present.
The loss of weight from evaporation occurs before the film begins to set, and then
an increase in weight, from oxidation, is noticed. As moisture accelerates the
drying process, it has been suggested that it acts as an oxygen carrier and also
provides a suitable medium for the action of the oxidase enzyme, * laccase/ At a
temperature above 63° C., laccase ceases to be active, and the drying occurs by
oxidation. When lacquer is mixed with Chinese wood oil (80 per cent lacquer to 20
per cent bodied oil) it dries more slowly than lacquer alone, but is satisfactory,
for the oil gives the mixture a high gloss, and the lacquer prevents the oil from
forming a wrinkled film.
According to the findings of Majima and Tahara (see Barry, pp. 141-142),
lacquer contains 90 per cent urushiol and 10 per cent hydro-urushiol. Chinese
lacquer was found by Majima to have a lower percentage, possibly because of
inferior methods of cultivation or of climatic differences. Yoshida lists the com-
position as follows:
Urushic acid....................85.15 per cent
Gum........................... 3.!5 " "
Nitrogenous matter.............. 2.28 " "
Volatile and water...............9.42 " "
Its density is 1.002. Tschirch, in his investigations, found that an oily, non-volatile
substance, which was soluble in petroleum ether, was responsible for the skin
poisoning which affects lacquer workers.
Lanolin (see Wool Wax).
^ Linoxyn (see also Oils and Fats) is oxidized linseed oil. This comprises a col-
loidal system which is by no means a simple mixture of organic compounds. In
its simplest terms it must be looked upon as a conglomerate of unsaturated
glycendes which have partially or completely undergone addition of a molecule
of oxygen at each double bond, together with the unsaturated glycerides which