The History and Production of Rose Madder and Alizarin pigments
George Field (1777-1854), is credited as one of the most outstanding colourmen of his age. Field spent many years researching the preparation of madder and lake colours.
Lake colours are pigments made by fixing a dye onto an insoluble base, such as hydrate of aluminium or sulphate of calcium. Field in fact wrote 10 volumes of notes and experiments on how to improve the quality of pigments. These books were purchased by William Winsor, co-founder of Winsor & Newton, after Field's death in 1854.
Field focussed heavily on pigments extracted from the Madder plant. Madder, more specifically, Common Madder (rubia tinctorum) is a small herbaceous plant, native to Asia and Southern Europe. One volume of his notes contains over 800 references to Madder alone.
This important dye had been used for more than 5000 years on fabrics and its use as a lake pigment dates from the 7th Century BC. So significant was Madder, that imports into the Great Britain were valued at £1.25 million per year in the 1860s.
Pigments made from Madder root, varied from rose to brown and were used by contemporary painters of the day, amongst them Constable and Holman-Hunt.
|Madder root and pigment
To increase the speed, quality and efficiency of pigment production, Field designed a lake "laboratory", shown in one of his notebooks dating from 1809. It is this layout, of a three tier system, that Winsor & Newton based their own lake laboratory upon.
Due to this, real madder, not a synthetic one, has been in constant production by Winsor & Newton since 1835.
For a pigment to be suitable for artists' colours, certain criteria are essential. Namely hue, colour strength, brightness, transparency, lightfastness, ease of dispersion and particle size. The method of manufacture has a critical effect to most of these.
The natural colouring matter of Madder is ruberythric acid - a clycoside of a number of anthraquinone dyes and mono saccharides (cellulose derivatives), the main dyes being:
|Alizarin - 1,2 - dihyroxyanthraquinone
|| Purpurin - 1,2,4 - trihyroxyanthraquinone
In 1826, two French chemists, Jean Jacque Colin (1784-1865) and Pierre Jean Robiquet (1780-1840), were the first to isolate the two main dyes, namely the alizarin and the purpurin.
Their findings were published 1827, in Annales de Chimie XXXIV, "Recherches sur la matière de la garance". ["Research on the subject of Madder"]
For the production of the pigment for Genuine Rose Madder [Natural Red 9], it is important to separate the cellulosic materials from the dyes, the main methods being:
- Fermentation (enzyme)
- Mordant extraction
Aluminium hydroxide gives the optimum transparency, so the dye is extracted using alum. The lake pigment being formed by precipitation with alkali. It is important to avoid metal impurities as these can alter the colour. However, intentional addition of metal salts can be used to produce other colours, such as brown madder and purple madder.
The pigment is also washed free of soluble salts produced in the precipitation process and then the final pgiment is produced by means of a purification process. The total process produces pigments for both oil and water colours, by slight modifications to the precipitation process.
The illustrations show the rose madder water colour wash and its spectral reflectance curve.
|Washes and curve
The total process takes about 13 weeks, which produces pigments for both oil and water colours, by slight modifications to the precipitation process.
Many other methods old and new have been tried to produce the pigment, however, none have been found to match the unique properties of the Rose Madder produced following Fields methods.
In 1846, Henry Edward Schunck (1820 -1903), a British chemist with a keen interest in dyes, started his own extensive research into the colouring materials found in madder.
Colin and Robiquet's analysis had given the formula C37H48O10. Using sublimation and crystallisation, Schunck obtained a result which appeared to be C14H8O4. However, taking into account the analysis of metal derivatives, he chose C14H10O4 as the best result. The modern formula is C14H8O4.
Schunck found by oxidising alizarin with nitric acid; alizaric acid (phthalic acid) was formed, which upon heating gave pyroalizaric acid (phthalic anhydride).
This discovery led to the suggestion that alizarin was a derivative of naphthalene, a C10 hydrocarbon, although Schunck pointed out that this did not explain the reactions of alizarin.
Schunck's findings were justified when Carl Gräbe (1841-1927) and Carl Theodore Liebermann (1842 -1914) distilled alizarin with zinc dust to give anthracene in 1868, subsequently synthesising alizarin from anthraquinone in 1869.
The principal synthesis entailed oxidation of anthraquinone-2-sulfonic acid with sodium nitrate in concentrated sodium hydroxide.
In studying the transformations of alizarin under the action of chemical reagents, Gräbe and Liebermann were led to connect it with anthracene and to devise a mode of forming it artificially.
Anthracene, is a solid polycyclic aromatic hydrocarbon (C14) consisting of three benzene rings derived from coal-tar.
This discovery was hailed as one of the most significant in dye chemistry as it presented a new route to the production of such a significant colour.
In addition to this, due the fact synthetic alizarin could be produced at less than half the cost of the natural product, the market for Madder rapidly declined. This meant large areas in France where returned to agriculture as appose to Madder cultivation.
Gräbe and Lieberman were working for the German company Badische Anilin- und Soda-Fabrik [Baden Aniline and Soda Factory (BASF)] at the time who, in 1869, patented their method of alizarin synthesis in England.
The English chemist William Henry Perkin (1838-1907), who was best known for his discovery, at the age of 18, of the first aniline dye, mauveine, had independently discovered the same synthesis. Unfortunately for Perkin, BASF filed their patent just one day before Perkin attempted to file his.
As with the natural madder lake, aluminium hydroxide is used as a substrate for the synthetic variety. The pigment produced (PR83) is most commonly used in alizarin crimson.
Gräbe and Liebermann's method for the production of synthetic alizarin starts by mixing one part of anthracene with four parts of sulphuric-acid. The resultant mixture is then heated to 212° C for between three and four hours, followed by an hour at 300° C.
Once cooled, water equal to three times the weight of anthracene and manganese equal to four times the weight is added.
This mixture is in turn boiled for three hours at which point milk of lime added. A deposit then forms consisting of the excess lime and manganese, along with a photodiode of manganese. A double sulphate of anthraquinone and lime remain within the solution.
The solution is now acted upon by an excess of carbonate of soda causing carbonate of lime to separate, producing a salt of soda. The salt of soda is then evaporated until dry.
The solid mass is then mixed with two to three parts of caustic soda and a small amount of water, which is in turn heated under pressure in a suitable vessel, at a high temperature.
This heat at pressure oxidises the anthraquinone converting it into alizarin.
Once cooled, the mass is dissolved in water and either sulphuric or acetic acid added causing an orange-yellow flocculent substance to precipitate.
The precipitant is then washed and dried to produce synthetic alizarin.
The synthetic alizarin appears identical and is chemically identical the alizarin contained within the colouring matter obtained from the Madder root.
Rose Madder & Alizarin in oil
Both also have comparative lightfastness.
However due to the absence of purpurin, the alizarin crimson is less saturated and brilliant when compared to the Genuine Rose Madder produced by laking.