34 PAINTING MATERIALS
facturers. Now only a small amount is collected in these islands. The bulk of it
comes from the Dutch East Indies, more than 75 per cent being estimated as
shipped from Macassar. It passes through many hands before its final shipment,
and it is probably adulterated to a considerable degree. This would account for
the many different properties ascribed by authorities to Manilla copal and the
difficulties in tracing a sample's origin. The wide varieties of commercial grades
come from the tree, Agathis alba (Lam.) Foxw., growing to a height of two hun-
dred feet, nearly that of the Kauri pine of New Zealand. Manilla is a soft copal,
and makes a less durable varnish than the hard varieties.
Mastic (see also Resins and Varnish) is a resin used chiefly in varnishes for oil
paintings. It comes from the tree, Pistacia Lentiscus, which grows in the Greek
Archipelago. It is also found in Portugal, Morocco, and the Canary Islands, but,
since the days of Dioscorides, commercial production has been almost exclusively
confined to the island of Chios. The trees are small and the resin, contained in the
bark rather than in the wood, is collected from numerous vertical incisions. Mastic
appears commercially in small, pea-like, transparent' tears/ of a pale straw color.
It is very fragile, and has an aromatic odor. Its melting point is very low (95° C.),
its specific gravity is 1.074, and, besides resinous constituents, it has a small
quantity of essential oil and moisture. It is almost entirely soluble in alcohol,
ether, chloroform, and ethereal oils, but the greater part is insoluble in petroleum
spirit.
Mastic, as well as dammar, may be used as a varnish ingredient, for certain
purposes as a paint medium, and as an addition to oil colors. The varnish produced
with mastic is light-colored, glossy, and elastic. It yellows with age, becomes
fragile and fissured, and blooms readily in a moist atmosphere. From old recipes
it seems probable that the varnish most widely used from the IX till the late XV
century was made by dissolving mastic, or both mastic and sandarac, in linseed
oil, often with the addition of a considerable quantity of pea grecay or colophony.
Today mastic is primarily used in spirit varnishes. A mastic-turpentine solution
is most common because it does not dissolve dry paint. To increase its elasticity,
elemi resin, linseed oil, or Venice turpentine is sometimes added (see Megilp).
Doerner (p. 130) recommends the following proportions: for a picture varnish
and painting medium, i part of mastic is dissolved in 3 parts rectified or doubly
rectified oil of turpentine. For a tempera emulsion, the proportions are I : 2. The
commercial mastic varnishes are usually prepared by dissolving the resin in hot
oil of turpentine. They are sticky and very yellow, characteristics which, according
to Doerner, come from the method of preparation as well as from the probable
use of inferior resin. He maintains that cold-prepared varnishes are almost color-
less and remain so. Mastic and sandarac are easily confused. Mastic, however,
softens when chewed, whereas sandarac powders. The colors, also, are different,
sandarac becoming darker and redder with age.