Kauri resin is sometimes spoken of as dammar, but this name properly belongs to the resins produced by other trees, not by Dammar a australis. White or Singapore dammar is the resin of Dammara orientalis. It is soft, and may be scratched even by mica. 'Sal dammar' is produced by Shorea robusta, the sal tree, widely distributed in India. This resin, though soft, yields a good flexible paper varnish. The tree belongs to the Dipterocarpeæ. Vateria indica, another Dipterocarp, yields piney resin or white dammar: a similar resin is produced by another species, V. acuminata, a Ceylon tree. Several kinds of Hopea (H. micrantha, H. odorata, etc.), which belong to the same natural order, yield pale, transparent resins which are a trifle harder than that of the sal tree. Black dammar or Tinnevelly resin is produced by Canarium strictum; it is of very inferior quality. This tree belongs to the Burseraceæ: several kinds of elemi resin are also furnished by plants belonging to the same natural order. These elemis are soft, sticky resins, occasionally employed in varnishes to prevent them from becoming brittle and cracking.

They contain essential oils and other aromatic bodies, and vary very much in composition and properties, although they resemble one another in their solubility in boiling alcohol and in their easy alterability. They are unsatisfactory resins.

The resin first known as sandarac was probably juniper resin, although the name was also applied to amber. It is spoken of by the older authorities on painting as having a red colour. Its hue is a dull reddish orange, and it yields a dark-brown varnish when dissolved by the aid of heat in a drying oil. The effect of this varnish in imparting an agreeable warm tone to pictures painted in tempera is very evident, when the cold aspect of an old Italian unvarnished tempera picture is compared with the glowing colour of a painting which still retains its original sandarac varnish. The resin now called sandarac is produced by another coniferous plant (Callitris quadrivalvis), a native of Algiers. It is a pale yellow resin, when fresh resembling mastic in colour, but becoming yellower with age. It is brittle and melts easily. When finely powdered and sifted it forms one of the kinds of pounce used in preparing the surface of parchment and vellum for writing and illuminating. It dissolves in alcohol and in acetone, incompletely in petroleum spirit and benzol.

There is one more resin which requires mention. This is mastic. The best and most important sort of mastic is produced by a small tree (Pistacia Lentiscus), belonging to the cashew-nut order or Anacardiaceæ. This tree occurs in Scio and other islands of the Greek Archipelago. Mastic exudes in the form of tears from incisions made in the bark. It occurs in small pea-like masses, and presents when fresh a very pale straw-colour. It is so fragile that it may be crushed to powder between the fingers. It has an aromatic odour, and dissolves completely in boiling alcohol and in spirits of turpentine. Its melting-point is low, on an average about 110° C. It contains, besides its resinous constituents, a small quantity of a volatile essential oil (a terpene) and of moisture. It yields a tender but glossy varnish, largely employed for the final protection of pictures in oil. This varnish yellows with age, and becomes fragile and fissured.

Resins, sometimes called mastics, are produced by other trees of the same genus. These resins, which are of no value for artistic purposes, are:

Indian mastic from Pistacia cabulica. Bombay mastic from P. Khinjak. Pistachio mastic from P. Terebinthus.

In the following table, compiled from the results of Böttler, are comprised some particulars concerning twelve of the resins commonly called 'copals.' In the first column the names are given, in the second the melting-points, in the third the relative hardness (12 being the hardest), and in the fourth and last column the degree of solubility (xii being the least soluble). The specific gravity of these copals depends so much upon the relative freedom of the several kinds from cavities and bubbles that the figures for this character are not included in the table. It may, however, be mentioned that all these resins are rather heavier than water, their specific gravities ranging from 1.035 to 1.07.

All these numbers are approximative only; and the valuation of these resins for varnish-making ought to take into account other properties not here recognised, such as toughness after as well as before heating and solution, liability to darkening in colour by lapse of time, and durability.