(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)
Three grades of paint seem to have developed particularly in North America: artist (finest, extra‑fine, super‑fine), professional (fine), and student. Ideally, artist‑grade paints are made with only the purest, highest‑quality ingredients, and manufactured without regard to cost. The paint is manufactured according to the tradition that each company has established for itself and upon which it rests its valuable reputation. A line of artist grade paints includes a large array of traditional and modern pigments, predominately composed of single pigments. For example, out of 132 colors of Lefranc & Bourgeois Extra-fine Oil Colors, more than 80 are single pigments. Single pigment colors allow you to mix to a large variety of secondary colors. Premixed colors are useful when you are looking for a color that is difficult to make, but undesirable for mixing with each other because they often produce “mud,” all but useless brownish gray. The pigment concentration can reach as high as 75% to oil and other ingredients in some colors.
Large manufacturers of artist grade oil paints frequently offer a professional grade paint as well. With professional grade, cost is major factor, but it is not the bottom line. This paint is designed to come as close to artist grade in quality, but not price. The level of craftsmanship varies, some manufacturers still grind their paints to the same degree as their artist grade, where others do not. In this grade, the range in colors is significantly reduced, with exotic pigments absent. Single pigment colors comprise 1/3 to ½ of the line, the balance of the color range is divided among colors with two to three pigments mixed together. This significantly increases the likelihood of mixing two colors together and getting mud instead a desired color. In professional grade the average pigment concentration is less, closer to 50% pigment to other ingredients. Fillers like aluminum hydrate are commonly used to some degree. Although professional grade is not as fine as in artist‑grade paint, it is safe to use, and without extensive testing the average painter using a limited range of colors would be hard pressed to tell the difference. Since white is generally the bulk of the paint used in a painting, and the difference in price between artist grade white and a professional grade white is small, one should consider only using artist grade whites.
Student grade paint varies widely in quality, from passable to simply awful. Student grade paint is made with the least costly raw materials and with the most cost‑effective methods, and price is the bottom line. Most of the colors are composed of more than one pigment, frequently three. Tradition mineral pigments like cadmium and cobalt are frequently replaced by cheaper modern substitutes, such as azos for cadmiums. Azo pigments tend to be duller, more transparent, and when mixed with other colors imparts a slightly unnatural appearance. This grade is loaded with fillers and oil and therefore has questionable longevity. Student paint lines are viewed as tools for studies or learning exercises where the final product will be discarded. Yet, it begs the question of what exactly is learned by using this grade of paint? What other profession teaches it students with substandard tools that perform completely different than the tools they would, and should, use as professionals?
The purpose of having this information about grades of paint is to help you make an educated choice. You may wish to choose the azo‑pigmented color over the cadmium‑barium color for aesthetic reasons. Unless you are among the most successful, price will be a factor in making your decision, because the finest cadmium red paint is expensive. If you paint large pictures, which have to be viewed twenty to thirty feet away, the difference between the best cadmium paint and one that is slightly impure cannot be seen.
Although student grade paints should not be used for professional work, choosing between profession grade and artist grade can simply be based on whether you can or cannot see and feel the difference. If you wish to test for yourself you can begin with such colors as manganese blue, cobalt violet, cadmium red, and Vandyke brown. The greatest differences can often be found with these colors. You can make a comparison of one or more of these colors by spreading some of each color on a clean sheet of glass with your fingertips. (Wash your hands thoroughly afterward.) If it is not ground well you can frequently feel the grit and if it is too oily you can usual feel that as well. Let the colors dry and then inspect them again. If you cannot see, feel, or care about the difference, then it is pointless to buy the more expensive paint.
Mixing one brand of artist grade with another, is not a problem. For best results it should be done within the same system: drying oil with drying oil, resin-oil with resin-oil, etc. The same is true within professional grades and student grades. When you mix different grades of paint, the general rule is that you reduce the quality of the better grade more than you improve the quality of the lesser grade. Notwithstanding, if you are going to intermix it only makes sense to mix artist grade with professional grade. To save money, many artists underpaint with either acrylics or profession grade oils, and reserve their finest paints for the upper most layers where the viewer might perceive a difference.