MATERIALS & METHODS - Painting - Oil Painting
Characteristics - Painting Methods & Techniques - Materials and Equipment - Work Space & Storage - Manufacture of Pigments - Protection of the Picture
Oil colors are made by mixing an adequate amount of cold-pressed linseed oil with a pigment to make a smooth buttery paint. When the paint is applied to a surface, the oil absorbs oxygen from the air and polymerizes to form a solid film, which binds the pigment to the canvas or panel. The dried film is tough and flexible, resistant to abrasion and water, and is not easily soluble in normal diluents, such as turpentine. The paint will keep well for long periods when stored in containers, such as tubes or jars, that exclude the air. It is desirable to use only as much oil as is absolutely necessary to bind the pigment in a film of good flexibility and adhesiveness. Since all linseed oil yellows to some degree the more oil that is used in the paint, the greater the amount of subsequent yellowing.
Pigment ground with a drying oil may settle out of the oil paint after prolonged storage, leaving excess oil at the top of the container and poorly bound pigment at the bottom. To prevent this, a small amount (about two percent of the volume of the paint) of a material called a stabilizer is added, which causes a better dispersion of the pigment in the oil and therefore gives the paint better quality. It may also impart a buttery quality to certain colors which otherwise grind out in either a stringy or an excessively liquid consistency. Aluminum stearate and beeswax are materials frequently employed as stabilizers.
Industrial manufacturers of artists' colors must consider certain problems of distribution . . . . stabilizers may be used more generously than would be necessary if a color were to be used up immediately after it was made.... are under some pressure from artists consumers who are often not too well informed as to the natural character of their materials, to provide colors that are all of the same buttery consistency and the same drying rate, regardless of the natural tendencies of the various pigments. For these reasons some manufacturers may resort to driers and "modified" linseed oils more than they would under ideal circumstances.
It must be kept in mind, however, that color manufacturers now have at their disposal machinery that can be controlled to produce minute changes in the character of their products. They have behind them the accumulated knowledge of generations of artists and color makers concerning standards of quality and sources of supply. They often subsidize research staffs of chemists and technicians to maintain the necessary quality control and standardization to compete with other manufacturers. Above all, they know that their reputation and long-range economic survival depend solely on the quality of the paint that they produce. Although an artist's ignorance of materials may be sometimes overlooked because it is balanced by expressive strength and painterly skill, no such refuge exists for the commercial color makers. For the sake of their reputations they must try to turn out a superior product. There is no question that they are capable of doing so when they see a demand for it.
On the other hand, there may be several reasons for artists to grind their own colors . . . . First, there is economy. For a very small outlay of money for materials and with the expenditure of a relatively small amount of labor, artists can produce in their studios very acceptable paint at a fraction of the cost of commercial color. Since it need not contain much stabilizer, it may be stronger, to a surprising extent, than comparable commercial "student-grade" paint. Second, by grinding their own colors, they gain knowledge of the nature of their ingredients and can better understand how they can use and modify even the industrially manufactured products. Third, they can obtain colors produced, so to speak, to the specification of their own techniques and styles . . . . by manipulating standard materials, they can make a color that is faster or slower in its drying, more or less buttery, or more or less fusible. [pp. 56-57]
[Kay, Reed. The Painter's Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983. pp. 127-129]
Consistency of Paint
All pigments do not react with oil in the same manner. Some, such as white lead, will produce very good paints, smooth and short [buttery]; others, such as ultramarine, have a tendency to be long and stringy; still others, like cobalt yellow, are inclined to become grainy or crystalline. Artists can accommodate their painting manipulations to the various natural characteristics of the individual pigments, as was done to some extent in the past. However, today the manufacturer has learned from long experience how to turn out a whole set of colors, all of which come out of their tubes in much the same consistency, with a close similarity of handling properties, and within a reasonably close range of drying speeds. The manufacturer gets these results by manipulation of mixing and grinding operations and by the addition of modifying ingredients. These added materials should be chosen from time-tested ingredients known not to be detrimental to the permanence of the finished painting. It is permissible to adjust the properties of paints with them, provided that they are not used in excessive amounts. [p. 98] [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.]
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