The Chemistry of Paints and Painting is a free textbook on chemical aspects of painting. See the editorial for more information....

Turpentines and Balsams

There is a group of substances, many of them derived from coniferous plants, which are, or have been, included under the term balsam. Strictly speaking, this designation should be limited to those resinoid exudates which contain benzoic or cinnamic acid, while the term oleo-resin, or, better still, the term turpentine, should be given to those soft and semi-liquid natural exudates which consist of terpenes associated with bodies of resinous character. The word turpentine is, however, so generally connected with the volatile hydrocarbons (terpenes) distilled from these exudates, that it should be clearly understood that the three vegetable products hereunder described are of natural, not artificial, origin. It is in consequence of the preservative influence upon certain pigments which has been assigned, not without experimental confirmation, to these bodies that they are noticed here.

Venice Turpentine. Under this name the resin of the common larch is now known. It comes chiefly from Tirol. Recent examination has shown it to consist mainly of three groups of compounds, namely, about 63 per cent of resinous acids, 20 percent of terpenes, and 14 percent of resins. The best specimens are never quite so clear and free from colour as those of the next product to be described.

Strasburg Turpentine is derived from Abies pectinata, the silver-fir, the best quality coming from the Italian side of the Tirolese Alps. It contains about 57 percent of resinous acids (not identical with those in larch-turpentine), 28 percent of terpenes, and 13 percent of resins. This turpentine is the true Olio d'Abezzo of Italian writers, and when dissolved in a terpene was used as a varnish for pictures in tempera and oil, and for the special protection of verdigris and of some other dangerous pigments. Some specimens of this turpentine are beautifully clear and colourless. It is decidedly superior to larch turpentine, with which it has no doubt been often confused, and to Bordeaux turpentine, obtained from Pinus Pinaster. The chemical study of the olio d'abezzo has at present thrown no light upon the specially protective or locking-up qualities which are claimed for this turpentine.

Canada Balsam, from Abies balsamea, much resembles Strasburg turpentine. The resinous acids which constitute three-fifths of its weight are said to be different from those already mentioned as existing in the turpentines from the larch and silver-fir.

Last Update: 2011-01-23