Genuine Vermilion and Cinnabar
For artists’ grade color, use the best grade of vermilion known as Chinese, or high quality native cinnabar, both of these pigments are available from Natural Pigments. Vermilion is the name of the artificial pigment, while cinnabar is the designation of the native mineral, both of which are chemically red mercuric sulfide (II).

To grind vermilion or cinnabar, 86 parts by weight of the dry pigment to 14 parts by weight of linseed oil, walnut oil or poppy seed oil is about the right proportion for mixing. Due to the heavy specific gravity, the pigment separates from the oil in tubes and some have resorted to using wax with the oil to keep pigment and oil together in storage, and while this can be employed successfully, you may have trouble with the color on account of the presence of the wax. The drying of oil can be seriously impaired by wax. Stearates are also effective in preventing separation. A better and safer plan is to grind the pigment in part linseed oil, walnut oil or poppy seed oil and part heat-bodied linseed oil, such as is used in making lithographers’ ink. The proportion of the two oils varies considerably depending upon the viscosity of the heat-bodied linseed oil. You can later thin this color with gum turpentine for easier brushing without impairing the gloss or life of the color.

…cold pressed linseed oil… I think it is the ultimate for oil paints, though other binders are more than satisfactory.

Why do you think cold-pressed linseed oil is the “ultimate” for oil paints?

I infer from your question, you have other views to my own (prejudices, misconceptions?) on this.

No misconceptions or prejudices about cold-pressed linseed oil. We have gained much experience in making paint using a wide range of pigments and variety of oils. We have noticed that there is a pervasive concept that cold-pressed linseed oil is the best to use for making one’s own paint. Some cite different reasons with offering much rationalization. Others cite that it has greater pigment wettability than other oils due to the high acid content. The interesting thing is that almost none of the paint manufacturers use cold-pressed linseed oil to make paint. One would wonder if all the paint manufacturers are wrong and a small group of artists are correct. So why is this? There are a wide range of industrial linseed oils available to paint manufacturers that offer high acid content, yet have been suitably aged and refined to remove the “foots” or mucilage. There is very little color in these oils and they handle quite well on the brush. Whereas, raw cold-pressed linseed oil has a high acid content, it is very yellow and contains many impurities that must be removed.

I have heard and my limited experience has shown that cold-pressed linseed has quite different characteristics from other binders. It has I believe a different more intense light refractivity, than say safflower.

What other binders have you compared it to? More intense light refractivity? I am not sure how you mean this in this context. If you are referring to the refractive index of cold-pressed linseed oil as compared to that of refined linseed oil or aged linseed oil, then there is almost no difference, none at least this is perceptible by the unaided eye. The difference between it and other drying oils is also small and would only make a difference with pigments that have very low refractive indexes, not most whites like lead white and titanium white.

The point is that while the romantic appeal of refining your own raw, cold-pressed linseed oil and the excitement of seeing mucilage separate from solution may be overwhelmingly popular for some artists who also claim to get back to the roots of art (funny thing is that these same artists only use modern synthetic pigments with this homegrown oil), it is not necessarily achieving a superior paint binder. Refined linseed oil with medium acid content makes a superior paint, because it yellows less, forms tougher paint films and contains sufficient acid to wet even the most finely divided organic pigments.

How much hand grinding is needed to form satisfactory pigment dispersions in drying oil vehicle? Moreover, how can you tell when sufficient grinding has been done? The answers to these questions are not simple to provide and depend upon the pigment and vehicle selected for hand grinding. However, I can provide some general guidelines that may help artists in this task:

When adding oil to the pile of dry powder pigment on the stone slab or glass plate, do so drop wise (drop-by-drop), mixing the oil with a spatula or palette knife, until all the pigment powder is incorporated and the mixture has a stiff, dough-like consistency. DO NOT ADD MORE OIL TO THE MIXTURE AT THIS POINT. The mixture will appear too stiff for painting, but this is all right, because the stiff mass creates more shear forces as it is kneaded and, as the pigment particles are wetted, it will relax and become more plastic.

Knead this mixture for some time with the spatula or palette knife, carefully observing changes in the consistency of the mass. For most pigments, you should observe a slight yet noticeable change from a stiff consistency to one that is softer and plastic. Continue kneading the mass, as the change in consistency indicates that agglomerates of pigment particles are breaking down into smaller ones and more pigment particle surfaces are being presented for wetting by the vehicle.

If you do not notice any further change in the consistency of the mass, stop kneading it with the spatula or palette knife. Some pigments, such as ultramarine blue or lapis lazuli (natural ultramarine blue), are refractory and difficult to grind to the right consistency. The best approach to grinding such pigments is to knead the mass until no further change is observed in its consistency and then allow the mixture to “sweat.” Sweating is a paint maker’s term for allowing the pigment-vehicle mixture to stand for a period. Cover the mixture with a plastic film and let it stand overnight. Some pigment agglomerates simply require time to allow the air in their interstices to escape and for the vehicle to wet their surfaces.

If the well-kneaded mass has the consistency of stiff yet plastic paste (somewhere between dough and toothpaste), then you are ready to begin grinding the mixture with a muller. If the mixture is too stiff for grinding with the muller, then add more vehicle drop-by-drop. Knead the mixture between drops of oil to check the consistency of the mass. It typically takes only a few drops to turn a stiff dough-like mass into a runny liquid so caution in adding more vehicle is necessary.

Stiff paste is the best word to describe the consistency of the pigment-vehicle mixture that is best suited for hand grinding with the muller. It should be slight more stiff than you would use for painting. It will become more fluid as you grind, so avoid the temptation to add more vehicle at this point.

Gather the mixture into a pile at the center of the slab or plate and begin grinding with the muller in circular motions. Some may advise that you grind in figure-eight motions or other fancy gyrations. It makes little difference as long as you grind all of the mixture thoroughly.

Periodically, using the spatula or palette knife, gather the mixture back together at the center as you spread it around on the slab or plate when grinding.

As you grind the mixture, you will notice a distinct change in the consistency of the paint:

[*]At first, pigment agglomerates will make small tracks in the mixture as you grind. You will see these begin to disappear entirely or at least become fewer in number. They may never disappear entirely, even if you grind from now until you wear a hole in the plate. Do not worry; you may never completely rid yourself of them and in themselves do not indicate a poor dispersion, because some may be large discrete particles of pigment and do not ruin the paint or decrease its brushability.

[*]Initially, the paint should have a stiff paste-like consistency. As you grind with the muller, the paint will become more plastic and flowing. If it becomes runny and liquid, then you may have added too much oil. No problem, because you can add more pigment to the mixture. The only problem with adding more pigment at this stage is that it will increase the time needed to grind the paint.

[*]The paint will usually have a dull mat surface before you grind. As the grinding proceeds, the surface of the paint will become glossy when you stop grinding and it is allowed to rest. This indicates that pigment particles are being wetted and are “sinking in” to the vehicle.

[*]There will be a distinct change in the sounds emanating from the grinding. It may initially sound like sand grinding on the plate surface and then soften and become more quite. This alone does not indicate that the paint mass has been sufficiently ground and a good dispersion has been achieved. The reason is quite simple; some pigments never cause the sound of sand grinding while others never quite stop making this sound. It all depends on the hardness of the pigment being ground. Some mineral pigments are very hard, such as azurite, malachite and earth pigments containing a small amount of silica (sand). In any case, a distinct change in the sound should be noticed while you are grinding with the muller.

If after grinding for some time the consistency of the paint does not soften to the viscosity that you prefer for painting, then add more vehicle, but do so drop wise and check the consistency after every one or two drops.

After observing the four characteristics noted above while grinding and you do not notice further changes in them, you most likely have achieved the best dispersion possible with hand grinding. You can congratulate yourself for hard work accomplished.