Natural Resins - Dammar

Wrap the clear lumps of resin in a piece of fine cheesecloth and tie the cloth so as to make a closed bag, leaving about a foot of string as a hanger. Put one pint of fresh turpentine into a clean, dry, wide-mouth jar. The jar should have a capacity of at least one quart. Lower the bag of resin into the turpentine. Punch a hole in the center of the jar lid and thread the string through this hole. Fasten it so that the bag of resin does not touch either the sides or the bottom of the jar. When the resin has dissolved, [p. 48] throw away the cheesecloth bag, which will contain a surprising amount of bark and dirt. If the resin contained much bark or other impurities, there may be brownish deposit on the bottom of the jar. This can be removed by allowing the solution to stand until all the impurities have settled. The clear varnish is then strained through cheesecloth into another container.

Caution: While the varnish is being made, do not allow any trace of water to come in contact with the jar, the turpentine, or the resin, lest moisture be trapped in the varnish, causing the film to dry with a bluish frost known as bloom.

The varnish is best stored away from light in containers that are filled so as to contain as little air as possible. Varnish in clear bottles left in direct sunlight for a long time may become darker and may not dry as well as freshly made varnish. Wrapping the bottle with opaque dark paper may help to keep the varnish in good condition over a longer time. To insure good drying characteristics of the varnish, the turpentine used to dissolve the resin should be fresh, clear, and of good quality.

Dammar varnish will brush out to a smooth, glossy, transparent coating and will dry very rapidly, since it hardens as soon as the turpentine evaporates from the film. It will darken to some extent with age, turning faintly yellowish brown, forming a film which is brittle compared to that of linseed oil. Like all simple solution varnishes, after its film has thoroughly dried it is easily redissolved by its thinner--in this case, turpentine. After the varnish has aged for many years, a stronger solvent is required to remove it.

For additions to painting media dammar varnish is usually made as a 5-pound cut. For picture varnish, painters reduce this to a 3-pound cut. Artists often prefer a more dilute picture varnish, made by reducing the dammar resin concentration to a 2 1/2-pound cut. For retouch varnish the concentration of resin is further reduced to a 1-pound cut.

These concentrations, or cuts, indicated in terms of pounds of resin per gallon of turpentine, can be made in smaller amounts with the following proportions of resin and turpentine.

Table 2-2
DRY RESIN, Weight - TURPENTINE

Stock, 5-pound cut 10 oz. [av.] - 1 pint
Picture varnish, 3-pound cut 6 oz. [av.] - 1 pint
Picture varnish, 2 1/2-pound cut 5 oz. [av.] - 1 pint
Retouch varnish, 1-pound cut 2 oz. [av.] - 1 pint

Sometimes it is more convenient to make up the varnish as a 5-pound cut stock solution. Then as various concentrations of varnish are needed, the stock solution can be diluted with turpentine as follows:

- For picture varnish [approx. 3-pound cut] add 1 1/2 oz. of turpentine to 4 oz. of 5-pound cut varnish
- For light picture varnish [approx. 2 1/2-pound cut], add 2 1/2 oz. of turpentine to 4 oz. of 5-pound cut varnish. [p. 49]
- For retouch varnish [approx. 1-pound cut], add 8 oz. of turpentine to 4-oz. of 5-pound cut varnish.

Application of the varnish is described [in a document titled: Procedures for Applying, which is filed in the Oil Painting Technique folder under Varnishes, in the Protection of the Picture folder.] [pp. 48-50]