(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)
Today, with the exception of a few pigments that are too delicate to be made other than by hand, oil paints are generally made by machine. For packaged paints, the machine process is far more effective than the techniques used in making paints by hand, and the range of available colors is much greater.
With the exception of a few delicate pigments such as genuine carmine, madder, and lapis lazuli (genuine ultramarine), the unromantic truth is that handmade oil paint is rarely as good as the finest machine‑made paint. The main reason is that machine grinding, or ball grinding, disperses the pigment particles and coats them more thoroughly with far less oil (excess oil means more yellowing and other undesirable effects) than could possibly be done by hand. Other drawbacks to making handmade paints are issues like storage, self-life, spoilage, and the considerable health hazards, acquiring the recipes with the proper ratios, wetting agents, pH buffers, preservatives, driers, and anti-foaming agents. Not to mention the knowledge and experience of how to combine all of them and the necessary tools to do it. As for saving money by making your own paint, most people who have tried it have found that for the average painter it is not worth it. During the 1960’s it was the rage in among New York artists to make your own paints, almost a status symbol. Those who did so apparently had disastrous results because they used formula found in books that where meant for machine grinding, when they used them for hand grinding their oil paint yellow badly and tended to shriveling in paint films.
The only reasons for an artist to make his or her own paint, in spite of all the obstacles, is either for the learning experience or to make a paint that cannot be bought, such as a resin‑oil paint or restoration paint.
Blockx paint is the last commercially available, extra‑fine, handmade paint. They claim to use a small amount of liquid amber medium. A precious and very desirable ingredient that would normally classify this paint as a resin-oil paint if not for the small quantity used in its manufacture. Because it is handmade, it is not only extremely expensive, but the range of colors is small by comparison to other lines of extra‑fine paints and finding a consistent supply of those colors is difficult.
Most commercial artist quality oil paints are made with some variation, or abbreviation, of the following description in large part is supplied by the artists material manufacturer Holbein Company in Japan.
The first stage is preparation of the mill‑base, a mixture of pigment, oil, wetting agents, and sometimes resins in ratios prescribed by the natural characteristics of each pigment, which is then placed in an agitator to disperse the ingredients evenly. Some pigments require a vacuum agitator to remove water and trapped gas. If the mill‑base is not properly prepared, the next stage of grinding will not be effective.
Additional medium and pigment are mixed with the mill‑base and fed into the first series of rollers to grind the mixture and produce a base‑paint. The purpose of grinding is to completely disperse each individual particle of pigment and coat it completely with the medium, or vehicle. This isolates and protects the pigment from reacting chemically with other uncoated pigments, and is what gives oil paint its brilliant quality. That quality is determined during this stage of processing. The rollers that grind the paint are made from iron, stone, and ceramic, and are used individually or in combination with varying ratios of revolutions depending on the nature of the pigment. Most pigments at this stage are ground three or four times starting with the iron, then the stone, and finally the ceramic rollers to make an artist‑grade paint. (Most manufacturers only use iron, some iron and stone, a few use all three). If there is too much grinding, the pigment will be pulverized and its brilliance lost, and if there is too little grinding, the paint will be oily and gritty. The grinding must not be hurried. Faster grinding means more friction and increased temperature to the point that it can cook the pigment and thereby alter its color.
The third stage is the adjustment process where the base‑paint is mixed with an antiseptic, an antifungal agent, driers (if needed), and stabilizers (such as wax, if needed), and is ground two to three times more. At this time, the color is also adjusted to match a previous company standard. The finished product is then tested for tinting strength, covering power, handling properties, resistance to putrefaction, and stability under exposure to light and variations in temperature. After quality control standards have been met, the mixture is aged, usually three to six months. This allows any excess oil to separate naturally from the pigment so that it can be removed before the final process of filling the tubes.
The manufacturing process described here is for an extra‑fine quality, or artist grade paint. Lesser grades are manufactured with substantially less grinding and quality control, as well as less expensive ingredients.
(Excerpts from ART HARDWARE: The Definitive Guide to Artists’Materials, by Steven Saitzyk © 1987 revised 1998)