Manufacture of Oil Colors

In the Studio

Dry Pigments. Only artist-grade pigments listed for oil technique should be used.

Thinner. Pure gum spirits of turpentine or mineral spirits.

Wax. Pure white beeswax

Tubes. 1' by 4' "studio" size, pure tin, aluminum or lead.

Oil. First choice, pure cold-pressed linseed oil; or if this is unobtainable, well-refined linseed oil, free from traces of chemical-refining agents.

Stabilizer. Painters who grind colors in their studios can employ as a stabilizer a paste made of beeswax dissolved in linseed oil. Such a paste may be made in the following way:

l. Measure into a metal container, such as the top of a double boiler, 7 fluid onces of linseed oil. Weigh out 1 ounce (av.) of beeswax, break it into smaller pieces, and put the wax into the oil.

2. Heat the mixture over an electric hot plate until the wax dissolves completely in the oil. Do not get the wax too hot or it may darken.

3. Shut off the heat and remove the mixture from the stove.

4. When the mixture of oil and liquid wax has cooled sufficiently, store it in a covered jar or tin can.

Grinding Oil. The pigments may be ground simply, using only pure linseed oil as the grinding oil, or if a stabilizer is desired in the finished paint, prepare the grinding oil by combining:

8 fluid ounces wax paste stabilizer [see prev. recipe]
24 fluid ounces [1 and 1/2 pints] linseed oil

Put the wax paste in a quart jar and stir it to be sure it is smooth and free of lumps. Add the oil gradually, a few ounces at a time, and stir the mixture so that the paste is evenly distributed in the oil.

When used with average pigments, this grinding oil will produce paints containing roughly 1 and 1/2 - 2 percent by volume of wax. Slightly more or less wax paste may be used, according to the nature of the particular pigment being ground.

[pp. 58-59]

Equipment

Spatula. About 6" by 8" long, flexible steel blade well riveted to a wooden handle. A professional-quality cooking spatula serves very well.

Scraper. 3" wide. A flexible steel wall scraper, used by house painters to remove wallpaper, is excellent.

Palette Knife. Straight blade, less than 1/2" wide.

Pliers. Artist's canvas-stretching pliers or upholsterer's pliers.

Grinding Muller. 3 and 1/2" face, made of glass.

Grinding Slab. 18" by 24" by 1/4" The grinding slab can be made of 1/4" plate glass, with edges that have been ground smooth and rounded slightly so they are not dangerous to handle. The surface of the slab should be prepared in the following way:

l. Put the slab on a solid table or bench and tack 1/2" wooden stripping around it so that it cannot move about on the table. Put a sheet of heavy cardboard between the slab and the table to act as a cushion and to prevent the glass from cracking.

2. Put a few tablespoons of medium-grit (number 40) carborundum on the slab. Add enough water to make a loose paste.

3. Using the glass muller, grind the paste with a circular motion over the slab until the whole surface of the glass has been roughened by the carborundum. This may take about 15 minutes. Rinse both slab and muller with cold water until all traces of carborundum paste are completely removed. Dry thoroughly with a clean cloth. When they are dry, both the slab and the face of the muller should have an etched, frosty appearance, and their surfaces should have sufficient tooth to grind the colors well. Clean all traces of carborundum from the bench.

This surface should last for many hours of grinding. If, after much use, it becomes too smooth, it should be roughened again with carborundum.

[pp. 57-58]

2. Take a small amount [about a tablespoonful] of color paste from the pile and put it on the center of the slab. Grind this with the muller, using light pressure and a circular motion, gradually widening the circle until most of the slab is [p. 59] covered with the color. Continue grinding over the color until the paste is very smooth and no grittiness can be heard as the muller goes over it. Use the spatula frequently to remove the paste that rides up on the sides of the muller and regrind this paste. Set the smooth ground color, which now can be called paint, in a pile on a corner of the slab opposite the color paste.

3. If the color becomes too liquid when it is ground with the muller, add more dry pigment to the mixed color paste before proceeding further.

4. Continue to grind small amounts of the color paste until all the color has been ground with the muller and is a smooth, buttery consistency that will stand up in peaks like commercially produced tube paints.

5. When all the paste has been thus ground into paint, mix it well with the spatula in the center of the slab or grind it quickly once more to insure a homogeneous quality through the whole batch. It is now ready to be put into tubes.

6. Hold the tube with the cap pointing down and the open end pointing up. Loosen the cap slightly to avoid trapping air in the paint. Use a narrow palette knife to feed the paint into the open end of the tube. Grasp the tube lightly around the cap and the collar, and tap the heel of your hand sharply against the table to make the paint settle into the cap end of the tube. Do not tap the cap directly on the table, or the tube will dent and crumple. As more paint is added, tap frequently to eliminate the air pockets in the paint. When the tube is filled up to about 1" from the open end, close the end by pressing down on it lightly with the edge of the spatula, about 1 1/2" from the end of the tube, to eliminate a little paint and all the air in the bottom of the tube. Take care not to cut the tube by pressing too hard with the spatula. Fold the [p. 60] end several times, using the spatula to obtain a straight fold. Crimp the folded end of the tube with wide-jaw pliers.

7. Close cap of tube well. Clean outside of the tube with a rag that has been moistened with mineral spirits. Gummed labels or masking tape may be applied to identify the color. [p. 61]

8. Clean the slab, muller, and tools with mineral spirits and rags. Then wash the equipment thoroughly with steel wool and soap and water or scouring powder. Be sure to rinse away all traces of the soap from the slab, tools, and muller. Dry well with clean rags before using the equipment for the next color. [pp. 59-62]

Notes
A. The brushing and drying character of the paint may be altered by changing the composition of the grinding oil used as a binder. [Kay, Reed. The Painters Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983. p. 62]

B. Addition of resin varnishes to the grinding oil will accelerate the setting of the color, inhibit "sinking in" of colors, and produce glossier films. Up to 10 percent of heavy dammar varnish to 90 percent linseed oil may be used. Sun-thickened linseed oil or stand oil may also be useful here.

C. Poppyseed oil may be added to the grinding oil to produce colors that will dry slowly and yellow somewhat less than they would with pure linseed oil. Poppy-seed oil also produces paints that are more buttery and "short" than those ground only with linseed oil, and so it may sometimes be added in small amounts [up to 10 percent] to the grinding oil when a pigment has a tendency to grind out to a stringy or runny state.

D. The grinding oil or binder should be prepared at least a day or so in advance to allow for complete assimilation of the ingredients.

E. Casein or egg emulsion is sometimes added to the colors to produce a "short" brushing quality.

F. Whiting may be added to "stretch" colors to be used for sketching paints or where permanence is not essential. Such additions cause the paint to yellow more with age.

G. Zinc white, viridian, ultramarine blue, and, occasionally, the yellow ochers should be allowed to stand for a day or so in closed containers after they are first ground in oil. If they revert to a more liquid consistency, they should then be reground with more dry pigment. Ultramarine in particular becomes so liquid and stringy that additions of wax stabilizer or poppyseed oil are required to give it a buttery consistency.

H. Manufacturers often use a white powder--aluminum stearate--as a stabilizer, in amounts up to 2 percent by volume of the total volume of paint. In oil colors this material is transparent and does not materially affect the color quality of the paint. However, just because of this transparency it does not hide the yellowing of the additional oil required to bind it into the paint film. Furthermore, its addition in any great quantity makes the paint film spongy or crumbly. For these reasons, although very small amounts can be accepted as useful, particularly in the case of certain "difficult" pigments [such as ultramarine blue], larger percentages are considered to be adulterations of the quality of the paint which will cause it to age badly.

I. Beeswax is more easily controlled than a aluminum stearate as a stabilizer in small batches of paint. however, as in the case of the other stabilizers, 2 percent of the total volume of the paint is usually considered the limit for improving it. Appreciable amounts in excess of 2 percent will result in a paint that may behave well initially but will age poorly and will be deficient in tinting strength. [pp. 62-63.]

Storage
Dry pigments are best kept in glass jars securely covered to avoid the absorption of moisture from the air. [p. 63]

Oils used as binders and diluents should be kept in full jars. As the oil is used, clean glass marbles may be dropped into the jar to maintain the level of oil in the vessel and thus keep out air.

Turpentine is best stored away from light and air in well-closed dark-glass containers. It should not be kept too long or it may become yellow and gummy.

Varnishes should be stored in tightly closed containers so that no water gets into the varnish. They should be shielded from strong light, especially if they contain turpentine. [pp. 63-64.]