Cassel Earth Pigment

Cassel Earth is a pigment of a deep semi-opaque brownish-black color, similar to the pigment used by Rubens and Anthony Van Dyke in their paintings. Rublev Colours Cassel Earth is imported from Italy.

Origin and History

Cassel earth, also known as Vandyke brown and Cologne earth, contains iron and manganese oxides and lignites, organic substances from peat or coal. It was first used in European painting in the 17th century and is still used today. This color is found in the pictures of the old masters, among them Rubens, who used it mixed with yellow ochre as a warm, transparent brown, which held up remarkably well in resin varnish.

Source

A brown earthy substance found in peat and lignite beds and used as a pigment; originally found near Cassel, Germany. Cologne brown or Cologne earth is a similar substance found initially near Cologne, Germany. The brown earth has since been obtained from various localities, which may differ slightly in color and composition. To add to this confusion, some pigments labeled Cassel earth or Vandyke brown are bituminous earth, typically composed of lignites. In contrast, other pigments labeled with these names are artificial pigments made from carbon black and iron oxide mixtures. When natural Cassel earth is ignited, the pigment leaves a soft gray residue. It is not soluble in petroleum solvents like bitumen. Lignite, also known as brown coal, is a brownish-black, heterogeneous mixture of compounds that have high inherent moisture and high ash content compared with bituminous coal. They are prone to alter color over time when exposed to light and humidity.

Rublev Colours Cassel Earth is a blend of natural iron oxides and burnt umber sourced from varied locales, notably Italy and Cyprus. The meticulous processing of this composite involves drying, pulverizing, and grinding to simulate the color and properties of genuine Cassel earth with exceptional precision. This thorough mixture ensures that the mixed pigment achieves the desired hue and upholds the distinctive characteristics associated with genuine Cassel earth.

Permanence and Compatibility

The blend of minerals composing Cassel earth is considered to be among the most permanent pigments on the artist's palette. The lignite portion of genuine Cassel earth has limited lightfastness, chemical resistance, and heat stability. Cassel earth (the lignite portion) is partially soluble in oil and may exhibit a slight tendency to turn gray (most apparent when mixed with whites). When used in an oil paint layer coated with spirit varnish or mixed with resin varnish, it is more permanent than when used in oil alone. It is sensitive to alkalis and becomes a cold gray in fresco. It can be used in oil, egg tempera, and watercolor but should not be used in fresco and casein tempera painting techniques. Unlike genuine Cassel earth, this blend from Itlay has no issues with permanence or incompatibilities with other pigments.

Oil Absorption and Grinding

Cassel earth absorbs a moderate to a large amount of oil, is a medium to slow dryer in oil paint, and forms a good film. The oil absorption ratio is 60–70 parts by weight of linseed oil to 100 parts by weight of pigment. Cassel Earth requires 60–70 grams of linseed oil to grind 100 grams of pigment to form a stiff paste if the measurement were grams. The pigment absorbs the oil with difficulty, so it is best to let the oil and pigment remain in contact overnight before grinding with a muller. The mixture before grinding may be quite thin, but after grinding, it will stiffen to a jelly-like consistency, which is the nearest state to a paste possible with this pigment. The finished paint may subsequently soften and become more fluid. Using boiled oils does not remedy this situation. From 25 to 50% of the weight of pigment of terra alba may be added to improve the physical characteristics of Cassel earth.

Colour Index

The Colour Index (Third Edition 1997) lists Van Dyke Brown or Cassel Earth as Natural Brown 8 (NBr 8) and lists Pigment Brown 7 (PBr 7) as iron oxides (the natural form usually also contains iron oxides and clays). This pigment primarily consists of iron oxide with smaller amounts of manganese oxide. This makes classifying this natural pigment difficult, which seems to be a common point of confusion among pigment and paint manufacturers. We have provided the Colour Index Generic Names (CIGN) of the latest component of this blend to assist its identification since many natural pigments are not pure compounds but mixtures.

Toxicity

Cassel earth is not considered toxic; however, one of its components, manganese oxide, is moderately toxic, and care should be used in handling the dry powder pigment so as not to inhale the dust.

Notes

1. The refractive index is based on the measured refractive index of umber, as discussed in A. Adam, P. Planken, S. Meloni, and J. Dik, "TeraHertz imaging of hidden paint layers on canvas," Optical Express 17, 3407-3416 (2009). Last accessed August 9, 1023.