George's Blog

Formulas for varnishes and mediums call for measurements that are often confusing for artists. For example, in his formula for a glazing medium, Ralph Mayer calls for a “5-pound cut” of damar varnish.¹ This measurement refers to the amount of dry damar resin with spirits of gum turpentine in a ratio called a “cut,” which refers to the amount of resin in pounds dissolved in a gallon of turpentine. This measurement is simple enough to use when preparing your own varnish, but what if you want to use a commercially-prepared damar varnish, such as Natural Pigments Damar Picture Varnish or Neil’s Best Damar Varnish? How do you know if it is a 5-pound cut?

You will notice in the information provided for Natural Pigments varnishes that the resin amount is identified as a percentage, such as 31% (w/v), where w represents weight and v is volume. This is a common scientific expression to describe the amount of solute² in a solution. This expression measures the amount of solute in grams and measures the amount of solution in milliliters. In our example, Natural Pigments Neil’s Best Damar Varnish is a 31% (w/v) solution. It contains 31 grams of damar resin for every 100 mL of varnish.

		weight of solute (in grams)
Volume percent	=		x 100
		volume of solution (in milliliters)

Because of the different units in the numerator and denominator, this type of concentration is not a true percentage. It is used as a quick and easy measurement because volumes are easier to measure than weights and because the density of dilute solutions is generally close to one gram per milliliter (1 g/mL). Thus, the volume of a solution in milliliters is very nearly numerically equal to the mass of the solution in grams.

What is a 31% solution in “cut” measurements? Neil’s Best Damar Varnish contains 31 grams of damar resin for every 100 milliliters of varnish. This amount of damar is equivalent to 1.09349282 ounces and 100 mL of solution is 3.38140227 U.S. fluid ounces. If we multiply the solution volume to equal one U.S. gallon, and use the same multiplier for the weight of the damar, we obtain 41.39 ounces or 2.59 pounds. This means that a 31% solution is approximately equivalent to a 2.5 pound cut (slightly more) of varnish. To use Neil’s Best Damar Varnish in Ralph Mayer’s glazing medium formula, simply reduce the amount of the turpentine from 5 fluid ounces to 2.6 fluid ounces to obtain the same results. Hence the formula would read:

Stand Oil 1 fluid ounce
Neil’s Best Damar Varnish (2.6-pound cut) 1 fluid ounce
Pure gum spirits of turpentine 2.6 fluid ounces
Cobalt drier 15 drops

Notes
1 Mayer, Ralph. The Painter’s Craft. An Introduction to Artist's Methods and Materials. Revised and updated by Steven Sheehan, Director of the Ralph Mayer Center, Yale University School of Art. New York: Penquin Group. 1948. 1991. p. 110–111. The formula for the glazing medium is as follows:

Stand Oil 1 fluid ounce
Damar varnish (5-pound cut) 1 fluid ounce
Pure gum spirits of turpentine 5 fluid ounces
Cobalt drier 15 drops

2 A solute is a substance dissolved in another substance, usually the component of a solution present in the lesser amount.