(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)
Ideally, little or no stabilizer should be used in an artist‑grade paint. There are certain pigments, when ground into linseed or poppy oil, that could either have a stringy consistency or a tendency to separate from the oil. Such stabilizers as waxes (beeswax or aluminum stearate), water, and alumina hydrate (added to give bulk) are currently utilized to regulate consistency. Although there are definitely cases where it is more helpful than harmful to have small amounts of these additives, the use of these materials has been abused, particularly in lesser grades of oil paint. Since these ingredients can be use to give a desirable consistency to an otherwise inferior paint, one has to look for additional clues to determine the quality of a paint.
Stabilizers easily cross over into use as fillers. It is considered acceptable by most manufacturers to use, for example, as much as 1 to 2 percent aluminum stearate, by weight, to improve the consistency of some colors. However, aluminum stearate weighs very little compared to the volume it can occupy. Aluminum stearate does to oil paint what goose down does to a comforter; it is easily possible for this wax to take two to four times its weight in volume. If an ” average” tube oil paint consists of 50 percent oil to 50 percent pigment by volume, the adding of 2 percent aluminum stearate, by weight, could reduce the volume of pigment by 8 percent to a total 42 percent. Although certainly significant, this is not serious. It becomes serious when more than 2 percent by weight is used, not only because it replaces more pigment, but because it becomes necessary to increase the proportion of oil to offset the increased effects of the aluminum stearate. If 5 percent aluminum stearate, by weight, is used, the result could be volumes of 70 percent oil, 20 percent aluminum stearate, and only 10 percent pigment.
No reputable manufacturer of artist grade paints would do this because most of the costs of making these paints is for labor, marketing, distribution, and not for materials. It would be pointless to scrimp on raw materials for the products for which their companies reputations stands. In lesser grades, however, where competitive pricing is so strong, the manufacturing process in less labor intensive, compromising on the raw materials becomes one the most effective ways to save money. Here is where an artist can protect themselves by doing tint tests.