A Basic Guide to Artist Pigments
Learn the Properties and Characteristics of Pigments and Dyes in: A Basic Guide to Artists' Pigments
What are pigments?
- Pigments are dry, powdery materials which happen to possess color. They come from many sources and they vary greatly in their characteristics.
- Pigments have little or no affinity for the surface onto which they are applied. The use of a binder (e.g. gum arabic, oil) is required to unite the pigment with the painting surface, whether it be paper, canvas, plaster or metal.
- Pigments are particulate materials which do not dissolve, but remain dispersed or suspended when mixed with a vehicle.
- Pigments are either organic (containing carbon) or inorganic (without carbon).
- Some pigments come from natural sources. Earth colors, such as umbers and siennas are really natural earth. Other pigments, such as the cadmium colors, are manufactured.
Comparing Pigments and Dyes
Dyes are used as colorants primarily in the textile industry and by designers and illustrators who prepare camera-ready artwork. Most dye colors are not permanent enough to be used for fine art applications where long term lightfastness is required. Two primary factors differentiate pigments and dyes:
Solubility - Dyes are nearly always soluble in the liquid into which they have been introduced, while pigments are nearly always insoluble.
Affinity - Dyes have an affinity for nearly any surface and will stain freely, with or without the addition of a binder. Pigments have little or no affinity for the surface onto which they are applied. To unite the pigment with the painting surface, a binder is required.
Dyes can be chemically converted into pigments for paints by Precipitating (separating them from their solution) and fixing them onto a colorless base so they become insoluble. The pigments obtained are called lakes, such as Crimson Lake or Alizarin Crimson.
Pigments fall into two basic categories: organic and inorganic. Organic pigments contain carbon. They tend to be transparent, light in weight and high in tinting strength-- especially those made synthetically. Inorganic pigments are mostly metallic compounds from metals. They tend to be opaque, heavy in weight and dense. Pigments with names like cobalt, zinc, iron, etc. are easily recognizable as inorganic.
Natural Inorganic Pigments
These are the natural earth colors (ochres, umbers, siennas), mined directly from the earth. Their color comes from the presence of iron oxides and hydroxides in the soil, along with varying amounts of clay, chalk and silica. When earth colors are calcined (roasted), their usual color becomes warmer and deeper, (e.g. calcined raw umber = burnt umber).
Synthetic Inorganic Pigments
These pigments are inorganic substances produced in the laboratory and are mostly metallic compounds (e.g. cobalt blue, manganese violet). There are also synthetic replications, like Mars Red and Yellow, of the natural earth colors. These factory equivalents contain fewer impurities and are smaller in particle size than their natural earth counterparts. Natural Organic Pigments. These are pigments of vegetable or animal origin, such as madder lake and ivory, bone or vine black, the last three of which are charcoals derived from the sources in their names.
Synthetic Organic Pigments
The list of synthetic pigments containing carbon (e.g. phthalocyanine blue, quinacridone red) continues to expand with the growth of organic chemistry. As a class, these pigments tend to be transparent, light in weight and high in tinting strength.
Factors For Analyzing Pigments
It should be noted that pigments used by different color manufacturers do vary slightly in specification and will yield slightly different results. This is especially apparent in tinting strength and permanence to light.
Actual tinting strength is tested by mixing the color with white paint, usually at a 1:10 ratio. Tinting strength can be affected by the pigment's particle size and the way it has been ground. Organic pigments, especially synthetic ones, are more likely to have a high tinting strength than inorganic ones.
Opacity is the hiding or covering power of a pigment and is dependent on the structure of its particles and on the vehicle used. Inorganic pigrnents are more apt to he opaque.
Transparency is the ability of a paint layer to contain so little pigment, or be applied so thinly that the layers beneath are revealed. While it is easy to apply a thin paint layer, it can be muddy if the pigment is not naturally transparent. Certain pigments, such as the synthetic organics, are transparent as a result of their molecular structure and are often referred to as glazing pigments.
Permanence To Light
The ability of a pigment to resist fading is referred to as lightfastness and is recorded two ways: mass tone and tint. Mass tone is obtained by using the pigment in its full strength. Tint is obtained by diluting the pigment in white. Some pigments may be satisfactorily lightfast in mass tone, but not in tint. The binder in which a pigment is dispersed can also have an effect.
This denotes the way a pigment affects the drying rate of the oil in which it has been mixed. Some pigments, such as vermilion, retard the drying process of the oil, while others, such as cobalt blue, accelerate the drying process. This information is invaluable to painters who use wet-in-wet techniques.
Oil Absorption (by volume)
The amount of oil required to properly wet and suspend a pigment varies. Artists should know which paints are "fatter" than others. The more oil the paint contains, the more it may be prone to cracking. This is why the rule "fat over lean" is important in oil painting.