Madder

Synonyms:

Madder, Pink Madder, Rose Madder, Madder Carmine, Madder Red, Rubens' Madder, Madder Purple, Madder Lake, Madder Brown, Carmin de Garance, Laque de Garance, Krapplack

Some authorities assert that madder was used in dyeing long before its employment in painting. But there is some evidence, derived from 'finds' of pigments and from paintings, that the ancient Greeks and Romans were acquainted with a pink pigment derived from madder, while there are good reasons for believing that such substances were widely known in Europe as early as the thirteenth century. Even in England, such a pigment is almost certainly referred to, under the name 'sinopis,' in the middle of the fourteenth century. Now Alcherius (close of fourteenth century) tells us that 'sinopis is a colour redder than vermilion, and it is made from varancia.' 'Varancia' is clearly garance, that is, madder, the same material being named 'warancia' and 'waranz' in a British Museum manuscript (Sloane, No. 416) which contains recipes of the fourteenth century. Besides 'sinopis' (strictly, a red earth), madder-lake was called, in English account-rolls of the fourteenth century, 'sinopre' and 'cynople.' It is, however, difficult, if not impossible, to ascertain the precise date at which pigments derived from madder came into use in the various schools of painting in Europe. For the nomenclature of pigments has always been somewhat vague, while the evidence furnished by existing pictures does not at present enable us to trace back with absolute certainty the mediæval use of madder paints to an earlier time than the fifteenth century.

Eraclius does not mention madder, nor does Cennini, who lived at a much later time. Mr. R. Hendrie, in his notes to 'Theophilus,' speaks of an English manuscript of the fourteenth century in which directions are given for extracting the colouring matter of 'madyr.' From these directions we are, perhaps, justified in concluding that the preparation of a kind of liquid paint was intended.

The European madder-plant, a native of Greece, belongs to the tribe Galieæ, of the order Rubiaceæ; it is the Rubia tinctorum of Linnæus. Several other species of this genus are used or grown in India for the sake of the red dye they afford. Among such species, Rubia cordifolia (Linn.) and R. sikkimensis (Kurz.) may be named, but the European madder is also cultivated extensively in India. Much madder was formerly grown in the Levant, in Holland, and in the south of France; but the manufacture by artificial means from the anthracene of coal-tar of its two chief colouring matters, alizarin and purpurin, has almost entirely extinguished the cultivation of the madder-plant in Europe. We shall have something to say presently concerning the artificial products above named.

The root of madder contains a much larger proportion of the colouring matters (or, it would be more correct to say, colour-making substances) than the other parts of the plant. They occur dissolved in the yellow cell-contents of the soft tissue of the root. The finest madder was grown in the 'Palud,' a chalky valley near Vaucluse. But the cultivation of this plant was carried out in great perfection in Zeeland during the eighteenth century.

The colouring matters obtained from madder exist in the plant in the form of glucosides. These glucosides are resolved by the fermentation, brought about by a peculiar ferment in the plant itself, and by many chemical agents, such as mineral alkalies and acids, mainly into glucose on the one hand, and on the other into the several colouring principles. Of such colouring principles the glucosides in madder yield at least three, of which the most important are these two:

1. Alizarin, C₁₄H₈O₄.

2. Purpurin, C₁₄H₈O₅.

Both alizarin and purpurin are now manufactured artificially from anthracene. This compound, which occurs in coal-tar, is a crystalline fluorescent hydrocarbon, C₁₄H₁₀. By a series of processes this substance gives rise to alizarin and purpurin, which are in all respects identical with these colouring matters as derived from the madder plant itself. The artificial alizarin of commerce contains several other colouring matters, two of which are better known than the others; these are anthrapurpurin (C₁₄H₈O₅) and purpuro-xanthin (C₁₄H₈O₄). Purpuroxanthin is also present in the natural pigments derived from madder, but it exists in small proportion. Of all these compounds alizarin is the most important and the best known, and yields lakes having various hues of crimson, rose, purple, violet and marone, according to its purity, its concentration, and the nature of the base (alumina, aluminium phosphate, iron oxide, manganese oxide, copper oxide, or lime with alumina) with which it is associated. The purpurin and anthrapurpurin resemble one another closely, and give pigments which are generally characterized by more orange or red hues than those obtained with alizarin.

The rose and pink madders and the madder carmines of commerce are generally so manufactured as to include, for their colouring constituents, much alizarin and very little purpurin. A few indications of the ordinary methods of preparing these lakes may first be given.

The material used is often that called 'madder flowers,' which consists of the finely ground dried root after it has been submitted to the action of dilute sulphuric acid and washed. Four pounds of this madder are taken and warmed for two or three hours on a steamer, with a solution of 1 pound of pure alum in 1 gallon of water. The mixture is placed in a filter-press, and the liquor obtained (which must be perfectly clear) precipitated by the gradual addition of a solution of sodium carbonate. The first portions of madder lake which fall, being the best, should be collected apart. All the precipitates should be thoroughly washed with rain or distilled water till the wash-waters are no longer troubled on the addition of barium chloride solution; they are then moulded into small cones, drops, or discs, and carefully dried at a moderate temperature. Another process for preparing madder lakes is a modification of the above. Four pounds of madder-root in powder, after having been fermented and then washed with a weak solution of sodium sulphate, are boiled for fifteen minutes with 4 gallons of a 10 percent solution of pure alum, the whole is filtered, and at a temperature of 45° partially neutralized with a solution in water of about 8 ounces of pure sodium carbonate.

The liquor is now brought nearly to the boiling-point; the madder lake which is then deposited is to be thoroughly washed and then dried: it is much denser than that produced by the preceding process. In the manufacture of alizarin lakes it is customary to introduce a small quantity of a preparation known as Turkey-red oil or sulphated castor oil. This is made into a soap and added to the alkaline solution employed to precipitate the lake.

By the employment in various proportions of solutions of alum and calcium chloride, by the substitution of sodium phosphate for the carbonate, and by choosing various qualities of madder-root, a number of hues and tints of rose and pink madder may be obtained when one or other of the methods above described is adopted. The oxides of iron, manganese and copper, when used in association with more or less alumina as a base for receiving the various colouring matters of madder, give other hues, including madder purple and madder brown.

But occasionally the pigments sold under these names are mixtures. For instance, burnt sienna and copper ferro-cyanide have been found in samples of madder brown; the presence of copper in madder brown seems, however, to be usual, but it arises from the employment of copper sulphate in its preparation along with alum.

From alizarin and from purpurin (either natural or artificial) lakes may be readily prepared by dissolving these substances in the smallest necessary quantity of an alkali, such as ammonia or sodium carbonate, and then adding a solution of a pure aluminium salt or some pure freshly precipitated and thoroughly washed aluminium hydrate. Another and more recent process consists in dissolving the colouring matter in a solution of sodium aluminate, and then precipitating the 'lake' by adding dilute sulphuric acid or, better, a solution of alum.

The best artificial alizarin of commerce occurs as a yellowish powder, presenting the aspect of raw sienna. It may, however, be obtained in yellow or orange red crystals, either by repeated crystallization from a solvent or by sublimation in vacuo. Its colour is always brighter than that of purpurin, which in powder has about the hue of Venetian red. But when solutions are made of these two substances in alkalies, then it is seen that the colours are reversed, alizarin yielding a crimson verging upon purple, and purpurin a red verging upon crimson. Differences of colour will be noticed in the lakes prepared with these two bodies. The directions for preparing pigments from the above-named bodies are practically identical with those already given in outline, but the minute details of manipulation can be learned only in actual practice. The following process gives an artificial red madder of excellent hue: Equal weights of pure alum (absolutely free from iron and lime) and of the purest artificial purpurin in powder are ground together, and then washed with cold water until the washings are colourless; then the residue on the filter is boiled with a 5 percent solution of pure alum, filtered while boiling, and immediately neutralized with pure sodium carbonate solution (also boiling) until red flocks appear.

These are filtered off, and constitute, when washed and dried, a fine pigment of a rich red hue. By heating the mother liquor to 80°, and adding more sodium carbonate, a further and equally good product is obtained. The purpurin residue, when again heated with more alum-solution and precipitated as above directed, yields a further quantity. The final residue, after several such exhaustions, produces an impure lake, having a brownish-red hue. A very large number of commercial preparations of alizarin and of other dye-stuffs closely allied to it are now available for the preparation of the so-called 'madder lakes.' Some of these preparations when dissolved and then precipitated on a suitable basis, yield pigments of great richness and stability, others, especially those which possess a yellow, orange, or red-brown hue, are less permanent. Here it may be remarked that, broadly speaking, the true or 'root' madders are complex so far as their colour-constituents are concerned and simple as regards their base, while the converse is true of the alizarin lakes.

Although the madder colours are very much less affected by light than are the pigments derived from cochineal, yet it cannot be affirmed that any of them are absolutely permanent when continuously exposed. The following figures show approximately the amount and nature of the change, observed after certain intervals, in the case of several madder pigments used as water-colours:

The letters A to F indicate different samples of the several pigments, which were in all cases 'moist' colours; a parallel but less complete series with 'cake' colours gave practically the same results. The five samples marked* are instances of exceptional stability, and are of importance as showing the possibility of obtaining some, at all events, of the madder pigments in a satisfactory form. It is noticeable that the paler (pink and rose) madders, which contain much water, are generally more perishable than the concentrated madder carmine; the comparative trials having, of course, been made with washes of nearly the same depth of tint.

A study of this table inclines one to think that the genuineness and purity of some of these pigments are doubtful, yet one specimen only (Madder Carmine C) was not tested. In this case the material used was not available for analysis, but I have no reason to doubt its authenticity.