The following is an email I received from Jim Flanagan with some insight on the qualities of organic and inorganic paint pigments. It has been edited and published with the permission of the author.
The differences between organic and inorganic oil paints is something most artists probably don’t know enough about. I only found out myself less than five or six years ago, but once I did it completely changed my palette and lowered my frustration level in achieving the effects I was trying to get with the paint.
Here are some basic facts:
These are natural pigments like the Cadmiums, Cobalts, Earth Colors, etc. They’re like tiny, opaque rocks and integrate well with mediums (both oils and acrylics) allowing a high pigment load. Organic based paints are also generally opaque which means they have strong covering power.
These are pigments created in the laboratory and include the Pthalocyanines, Quinacidrones, Dioxazenes, Napthols, etc.
Instead of tiny, opaque rocks like the natural colors mentioned above, these pigments resemble tiny, translucent chips of stained glass. They tend to be fussy when mixed with a medium and can’t reach the high pigment load enjoyed by organic hues. They also tend to be transparent, which means that they don’t have the covering power that the organics do.
What this means for the artist
The most important difference is the way organic and inorganic pigments act when you mix tints. If you squeeze out some Cadmium Red Light, say, along with a Napthol Red Light, you’ll see that both colors are somewhat similar in appearance in terms of hue, value, and intensity.
But (and this is a big but) when you start cutting the colors with white you’ll notice the intensity (or chroma) of the Cadmium Red drops off sharply as you lighten it in value but the Napthol red stays fairly vivid and intense when you do the same thing.
So if you want to create a light, warm pink for instance, with a fairly high intensity, you’d need to use an inorganic color to get this effect. Organic colors work for the most part in “realistic” paintings of nature because the intensity “fall-off” when mixing tints is naturally seen in nature.
On the other hand, a painter who desires expressive, high intensity colors at various value levels like I do can only achieve these affects with inorganic colors. When I need brilliant reds, oranges, or yellows (or need to cover another color) I’ll use the cadmiums but I rarely use them to make tints unless I want a softer effect.
Incidentally, one of my favorite daydreams is to go back in time to the late 19th century and give Van Gogh a big box containing a full range of modern professional oil colors. Maybe this would have kept him from shooting himself!
-Written by Jim Flanagan of FlanaganStudio.com