Indicum, on account of its long carriage by land, must have been dear, and therefore it was one of those pigments which the ancient painters, who were often poor slaves, were not accustomed to keep in any quantity by them, and with which it was necessary they should be supplied by those for whom they executed paintings[620]. Our indigo was also exceedingly dear till it was cultivated in the West Indies, where the value of it decreased as long as good land was plentiful and the price of labour was lessened by the slave-trade.
That indigo, which at present is used only by dyers, should have been employed also for painting, needs excite no surprise. It was applied to this purpose till the invention of painting in oil, and the discovery of Prussian blue, smalt and other pigments of a superior quality. It is even still used by landscape-painters to produce a pale gray; but it will not harmonise with oil. As to the medical properties of indigo, I can at any rate show that the experiments made with it at the end of the seventeenth and the beginning of the eighteenth century fully confirm the high encomium bestowed by Dioscorides upon his Indicum. There was a time when the former was much prescribed and recommended. At present our physicians are acquainted with purer and more powerful remedies than indigo, the internal use of which, as the fermented mass is prepared in copper vessels, must be attended with suspicion.
That the author, so often mentioned already, was not acquainted with the preparation of indigo, cannot be denied. It would, indeed, have been extraordinary had the account of it reached the Greeks and the Romans undisguised by fables, added either to answer the purposes of the interested merchant, or accidentally in the course of its long journey, in passing through so many countries and languages. It appears to me, however, that through these it may still be discovered; and in all probability we should be better able to form some idea of it were the oldest method of making indigo still known. In the slime deposited on the reeds, I think I can remark the first degree of fermentation, or commencement of putrefaction, without which the pigment could not be separated. Who knows whether the indigo plants in the earliest times were not deposited in pits or in stagnant water, in the same manner as our flax and hemp? Who knows whether after putrefaction they were not taken out, and the colouring parts adhering to them washed off and collected? The quantity indeed obtained by this process would not be great, and at present a much better method is employed; but the improvements made in every art have been gradual. The old inhabitants of the Canary islands scratched their land with the horns of oxen, because they were not acquainted with the spade, and far less with the plough. The above conjecture will appear much more probable, when it is known that in many parts of India the plants were formerly placed in large pits; and in Malta, where indigo was still cultivated in the seventeenth century, they were put into reservoirs or basins in order to ferment[621]. If this was usual in the oldest times, it may be easily seen how fabulous accounts might arise. Indigo was a slime attracted from the water by a reed, which the indigo plant, stripped of its bark, was considered to be.
Dioscorides speaks of another kind of indigo, which was the dried purple-coloured scum of the dye-pans. My predecessors, considering this account as an error, which might have arisen either from conjecture or misconception, or which was purposely occasioned by merchants, did not think it worthy of further examination. I cannot, however, refrain from remarking, that a blue pigment, and even a very fine one, if the proper preparations had been made for that purpose, might have been obtained in this manner. It was not indeed indigo, in the proper sense of the word, but a pigment of a similar nature. That fine high-priced powder sold, at present, under the name of blue carmine, is made from the separated scum of a dye-liquor, in which the finest colouring particles remain suspended. The scum or flower of a blue pan[622] which floats on the surface exhibits a play of many colours; and as among these the ancient purple is frequently observed, it may therefore very properly be said to have a purple colour[623]. In my opinion, there is no reason to disbelieve Dioscorides, when he says that in his time a blue pigment named indigo was made in this manner, especially as it can be proved that the woad-dyers, at the end of the sixteenth century, separated from their pans a colouring substance, which they sold instead of indigo, an article at that time exceedingly dear[624]. Besides, we read that in the establishments for dyeing black, the scum was in like manner collected in old times in the form of a black pigment, and this practice, as appears, was usual in all the dye-houses in general. Pliny, who says that this indigo was made in the purple dye-houses, seems either to have misunderstood Dioscorides, or to have been too precipitate; but it is certain that the scum in the purple dye-houses may have been collected and dried into a purple-coloured carmine.
As the Europeans did not become acquainted with the nature of indigo till modern times, it needs excite no astonishment that the old commentators should have erred in explaining the passages to which I here allude; and their opinion can therefore be of little weight in opposition to mine. Those who have approached nearest to the truth, Sarazen, Mathioli, Salmasius, &c., speak as if indigo were made from our woad, which however does not grow in India. Dioscorides speaks also of woad in a particular section. Marcellus Vergilius says, that Dioscorides meant indigo is certain; and this article is so generally known that it is not worth while to mention it. But he himself seems not to have been acquainted with it, else he would have amended the erroneous passage which speaks of Indian stone[625]. This arose from the ignorance of the old transcribers, who being unacquainted with Indicum thought only of gemma Indica, mentioned by Pliny[626]. But Vergilius was right in this, that the purple lake, spoken of by Pliny, and not by Dioscorides as he believes, can no longer be produced.
I have long made it a rule, and prescribed it to others, in explaining any object mentioned by the ancients, never to admit, without the strongest proofs, that the same article is denoted by different appellations. This, it is true, has been often done. By these means the small knowledge we possess of a thing that occurs under one name only may be increased. A wider field may thus be opened for conjecture, and more latitude may be given to the imagination; but at the same time one may fall into groundless explanations, and hazard assertions, which, with whatever caution and learning proposed, will, on closer examination, be found either false or highly improbable. According to this rule, I have carefully endeavoured not to suffer myself to be so far misled by the respectability of my predecessors, as to consider the Indicum and Indicum nigrum of the ancients to be the same substance. On further research I find that the latter not only appears by the epithet to be different from indigo, but that it is China, or, as the Dutch call it, Indian ink. To prove this, I must refer to the passage of Pliny[627] on which my assertion is founded; and perhaps the short illustrations added will render this minuteness less tedious to those who are fond of such disquisitions. In the passage referred to, Pliny enumerates all the materials which in his time were used for black ink. He therefore mentions two vitriolic substances, a slime or sediment (salsugo), and a yellow vitriolic earth (called also misy). Such minerals continued in use as long as men were unacquainted with the art of lixiviating the salt, and causing it to crystallize; or in other words, as long as they had no vitriol-manufactories. He speaks also of lamp-black being made in huts built for the purpose, which are described by Vitruvius, and from which the smoke of burning pine-wood was conveyed into a close apartment. The article was certainly adulterated, when soot, taken from the baths and other places where an open fire was maintained with wood of all kinds, was intermixed with it. It is very remarkable that black from burnt refuse of grapes, noir de vigne, which at present our artists, and particularly our copper-plate printers, consider as the most beautiful black, was made even at that period. Germany hitherto has obtained the greater part of this article from Mentz, through Frankfort, and on that account it is called Frankfort black. Some is made also at Kitsingen, Markbreit, and Munich. For this purpose the refuse of the grapes is charred in a close fire, and being then finely pounded is packed into casks. Pliny observes, that it was asserted that from this substance one could obtain a black which might be substituted for indigo. Another pigment was bone-black, or burnt ivory, which is highly esteemed even at present. Besides these, continues he, there is obtained from India what is called Indicum, the preparation of which I have not yet been able to learn: but a similar pigment is made from the black scum of the dye-pans, in places for dyeing black, and another kind is obtained from charred fir-wood finely pulverized. The cuttle-fish (sepia) likewise gives a black; but that however has nothing to do with the present question. He remarks, in the last place, that every kind of black pigment is improved, or rather the preparation of it completed, by exposure to the sun[628]; that is to say, after gum has been added to that intended for writing, and size to that destined for painting. But that which was made with vinegar was more durable, and could not be easily effaced by washing. All this is very true. Our ink acquires a superior quality when exposed to the light of the sun in flat vessels. That vinegar renders black colours faster, is well known to our calico-printers; and those who wish to have good ink must employ in making it the brightest vinegar of beer. It is equally true, that every black pigment mixed up with gum or size can be sooner and easier washed out again with water[629].
A considerable part of what has hitherto been quoted from Pliny, may be found also in Vitruvius[630]. The latter, in like manner, mentions huts for making lamp-black; he speaks also of ivory-black, and says expressly, that when it is properly made it not only forms a good colour and excellent ink, but approaches very near to Indicum.
Now I might here ask, whether it is at all probable that the learned Pliny and the practical connoisseur of painting, the architect Vitruvius, could consider and describe our blue indigo as a pigment which, like lamp-black, could be employed as a black colour and as ink? Is it credible that Pliny, if he meant blue indigo in the before-mentioned passage, would have said that he was not able to learn the preparation of it, when he expressly describes it, as he believed it to be, in the course of a few lines further? Would Pliny and Vitruvius, had they been acquainted with black indigo only, remark immediately after, that, when costly indigo could not be obtained, earth saturated with woad, consequently a blue earth, might be used in its stead? Is not allusion here made to a blue pigment, as was before to a black one? Is it not therefore evident, that the name of Indicum was given to a black and also to a blue pigment brought from India? And if this be the case, is it not highly probable that the black Indicum was what we at present call Indian ink, which approaches so near to the finest ivory-black, and black of wine lees, that it is often counterfeited by these substances, a preparation of which is frequently sold as Indian ink to unwary purchasers? Indian ink is in general use in India, and has been so in all probability since the earliest ages. In India all artificial productions are of very great antiquity; and therefore I will venture to say, that it is not probable that Indian ink is a new invention in India, although it may probably have been improved, and particularly by the Chinese.
To confound the two substances, however, called indigo (indicum) at that period was not possible, as every painter and dealer in colours would know that there were two kinds, a blue and a black. It has, nevertheless, occurred to me, that in the works of the ancients obscurity may have sometimes been avoided by the addition of an epithet; and I once thought I had found in Pliny an instance of this foresight; that is, where he names all kinds of colours—purpurissum, Indicum cæruleum, melinum, auripigmentum, cerussa[631]. I conceived that in this passage our indigo was distinguished from the black indicum by the epithet cæruleum. But my joy at this discovery was soon damped by Hardouin, who places between Indicum and cæruleum a comma, which is not to be found in many of the oldest and best editions. I cannot, therefore, get rid of this comma; for it is beyond all dispute that cæruleum was the common appellation of blue copper ochre, that is, mountain blue. I shall now proceed to examine whether my observation be true, that the Greeks frequently used the term black indicum, when they meant to denote the black, and not the blue.
The term nigrum Indicum occurs in Arrian, Galen, Paulus Ægineta, and perhaps in the works of other Greek physicians; and as the Latin writers were acquainted with an Indicum which dyed black, there is reason to conjecture that this was the Indicum nigrum of the Greeks, though I should rather be inclined to translate this appellation by the words Indian black, in the same manner as we may say Berlin blue, Roman red, Naples yellow, Brunswick green, Spanish brown, &c.; or I should as readily translate it Indian ink. Arrian introduces it along with other Indian wares. I do not indeed find that he makes any mention of indigo properly so called; but a complete catalogue of merchandise is not to be expected from him. Indicum, however, occurs once more in this author; but in the passage where it is found it is only an epithet to another article. Speaking of cinnabar, he adds, that he means that kind called Indian, which is obtained from a tree in the same manner as gum. I am inclined to think that he alludes to dragon’s blood, which on account of its colour was at that time called cinnabar.