Pyrrole Red Dispersion

The roots of the plant Rubia tinctorum supply the coloring substances that are converted to madder lakes, the principle coloring substance which is alizarin. The shades of colors of madder lakes vary from scarlet (stannous madder lakes), carmine red (carmine-containing madder lakes called madder carmine), pink madder (madder lakes with a high content of pseudopurpurin and/or purpurin called pink madder or rose madder), to red with a bluish tint (alizarin lakes).

Rublev Colours Aqueous Dispersions are pigments dispersed in water ready to be mixed with water-based mediums. These dispersions are especially made for use with traditional painting mediums, such as egg tempera, casein tempera, fresco, watercolors and distemper (glue tempera). They are also ideally suited for use with gesso to make toned grounds for drawing and painting. Pigment dispersions from Rublev Colours contain only naturally-derived ingredients, in addition to pigment and water, making them ideally suited for traditional mediums. Unlike other pigment dispersions that are typically made for acrylic medium, Rublev Colours Aqueous Dispersions do not contain coalescent solvents, artificial dispersing resins and other additives that interfere with natural mediums. Aqueous Dispersions make preparing traditional mediums easy; you do not have to hassle with powders, grinding pigments in medium and calculating binder ratios to make water-based paint. They make adding the right amount of paint binder, such as egg yolk, a no brainer because the right amount of water is already contained in the dispersion, simply add egg yolk.

Names
Common Names (Dyestuff):	alizarin, alizarine, purpurin, Rubia tinctorum
Common Names (Pigment):	English: madder lake French: laque de garance German: Krapplack Italian: lacca di robbia Portuguese: laca de ruiva Russian: крапплак Spanish: laca de rubia

Origin and History
Madder has been cultivated as a dyestuff since antiquity in central Asia and Egypt, where it was grown as early as 1500 B.C. Cloth dyed with madder root pigment was found in the tomb of the Pharaoh Tutankhamun and in the ruins of Pompeii and ancient Corinth. In the middle ages, Charlemagne encouraged madder cultivation. It grew well in the sandy soils of the Netherlands and became an important part of the local economy.

Thompson thinks that the madder lakes were less employed in medieval painting then were the brazil lakes. He says that pure madders, as they are known now, came into use in the 17th and 18th centuries and that they were not important in the Middle Ages [The Materials of Medieval Painting, pp. 123-124].

By 1804, the English dye-maker, George Field, had developed a technique to lake madder by treating it with alum. This turned the water-soluble madder extract into a solid, insoluble pigment. This resulting madder lake had a longer-lasting color, and could be used more versatilely, for example by blending it into a paint. Over the following years, it was found that other metal salts, including those containing iron, tin, and chromium, could be use in place of alum to give madder-based pigments of various other colors.

In 1826, the French chemist Pierre-Jean Robiquet found there were two colorants in madder root, alizarin and the more rapidly fading purpurin. The alizarin component became the first natural dye to be synthetically duplicated in 1868 when the German chemists Karl Graebe and Karl Lieberman, working for BASF, found a way to produce it from anthracene. About the same time, the English dye chemist William Perkin independently discovered the same synthesis, although the BASF group filed their patent before Perkin by only one day. The synthetic alizarin could be produced at less than half the cost of the natural product, and the market for madder collapsed virtually overnight. Alizarin itself has been in turn largely replaced today by the more light-resistant quinacridone pigments developed at DuPont in 1958.

Source
As an extract of the root of the madder plant, which was allowed to grow for two years in the ground, the root is not red itself, but contains alizarin, which can be made to produce red lakes of several shades and precipitated on a clay base.

Preparation of Lake Pigment
Pigments and dyes are not identical, although there are cases in which the same coloring matter which yields a dye or stain may give rise to a pigment. A pigment is, in fact, a substance which is insoluble in the vehicle with which it is mixed to make a paint, while a dye is soluble. A lake pigment is a natural organic pigment prepared when a dye has been precipitated on a powdered, colorless, inorganic substrate. The term derives from the Latin word lacca, used in the Middle Ages to denote both lake pigments and the Lac dye. Because of its transparency, aluminum hydroxide is the most commonly used substrate or carrier. Barites, such as barium sulfate, provide an opaque lake pigment. Other compounds used as carriers are: chalk, clay, gypsum, tin oxide, zinc oxide, white earth, and green earth. Often a mordant, such as tannic acid, lactic acid, or sodium phosphate, is used to fix the dye to the substrate. Madder lake and rose madder for artists' pigments are prepared from madder extract by adding alum and precipitating with an alkali.

Permanence and Compatibility
It is a beautiful transparent red, but impermanent. In the trade it is available as rose, light, medium to dark, and violet. Rose madder is known to fade within a few months of exposure to strong light, but the darker tones are more permanent. In fresco, lime destroys madder completely. In the original root there is a second coloring agent called purpurin, which when removed creates a superior permanence. Madder lake requires about 70% binder, dries poorly and should therefore be first mixed with linseed oil and ground with an addition of damar. It has been observed over time that madder lake bleeds, and when so it has been an indication that it has not been used properly, perhaps too thickly in underpainting, or that it has been mixed with impermanent coal-tar dyes.

Madder lakes, especially those that contain little or no purpurin have been well preserved in numerous European easel paintings, especially where it was employed as a glaze with another similar hue. Glazed over vermilion madder lake produces an intense cherry red unachievable by direct mixture of paints. Vermeer used this glaze in the plumed hat of his painting The Girl with a Red Hat and in the satin gown in The Girl with a Glass of Wine, both very well preserved.

Oil Absorption and Grinding
No data has been published on the oil absorption and grinding qualities of lake pigments made from madder root.

Toxicity
The essential coloring matter of the madder root is considered to be non-toxic.

Rublev Pigment: Madder Lake

Pigment Information
Color:	Red
Colour Index:	Natural Red 9 (75330, 75420)
Chemical Name:	Alizarin (1,2-dihydroxyanthraquinone), Purpurin (1,2,4-trihydroxyanthraquinone)
Chemical Name:	C14H8O4, C14H8O5
ASTM Lightfastness Rating
Acrylic:	III (alizarin)
Oil:
Watercolor:	III (alizarin)
Properties
Density:	�
Hardness:	�
Refractive Index:	�