jg PAINTING MATERIALS
As the term ' copal' is so commonly used for a variety of resins, tests have
been made to distinguish the true or fossil copal from such resins as dammar,
colophony, and Kauri and Manilla copals. True copal is insoluble in an 80 per
cent solution of chloral hydrate, but the other resins are partially or completely
soluble. The hard and soft varieties may be distinguished by treating a sample
with boiling water. After standing for half an hour, the hard copal remains un-
changed, whereas the soft copal becomes milky and opaque. The hardest copal
resin is Zanzibar; Sierra Leone and Kauri are of medium hardness; Manilla is a
soft copal.
Congo copal is the chief copal resin used in general commercial varnish manu-
facture today. It is practically the standard fossil resin. Copals appear in the
market in a variety of forms and colors. They may be had in large lumps or
pea-size * tears,' and they range from an almost colorless, transparent mass to a
bright, yellow-brown. They have a conchoidal fracture.
Copal resins make a thick, hard, dark, oil varnish. From varnish recipes of
the Middle Ages, it may be assumed that amber was often confused with copal.
The trade in copal probably began in the X century with the Arabs, but it is
mentioned only infrequently until the latter part of the XVIII century. It has
been used chiefly as a furniture and coach varnish. The old coach painters appar-
ently executed their designs in bright oil colors, freely mixed with turpentine.
This was coated with several layers of a spirit varnish, well rubbed down, and
over that was spread a copal oil varnish. Because of its tendency to become yellow
and dark, however, and because of the difficulty of dissolving and removing it,
copal varnish is not practical or useful as a varnish for paintings.
Crude Turpentine (see Balsam and Turpentine). This is another term for the
balsam in its natural state as it exudes from the pine tree. More commonly, that
is called ' turpentine,' c balsam,' or * oleo-resin.' The last two names are prefer-
able, for the common use of * turpentine * applies to * spirits of turpentine/
Dammar (see also Resins and Varnish) is derived from a certain family of
trees (Dipterocarpaceai) growing in the Malay States and in the East Indies.
The tree, Agathis Dammara, sometimes grows to a height of eighty or even a
hundred feet. From incisions the resin oozes readily in a soft, viscous state, with
a highly aromatic odor which it loses on hardening. € Dammar Mata Kuching,*
from Malaya, is known as ' cat's eye resin/ and is of a very high quality. It is
used for incense in the Orient, but appears in the European market in trans-
parent, brittle, odorless lumps for the manufacture of a spirit varnish. Its dis-
tinguishing characteristic is that it is completely soluble in coal-tar hydrocarbons
and in turpentine, and is almost completely insoluble in alcohol. It is light in
color, lustrous, and adherent The film is soft, however, is less durable than that
made from copal resin, and has a tendency to remain slightly tacky. Its paleness
and the ease with which it may be used have caused it to be very popular, and
it is regarded by some as the best varnish for pictures (see Maximilian Toch,