Green is obtained by dyeing a blue of the required shade in the indigo-vat, and then greening it with a good yellow dye, adding what else may be necessary (as, e.g., madder) to modify the colour according to taste.
Purple is got by blueing in the indigo-vat, and afterwards by a bath of cochineal, or kermes, or madder ; all intermediate shades of claret and murrey and russet can be got by these drugs helped out by " saddening."
Black, as aforesaid, is best made by dyeing dark blue wool with brown ; and walnut is better than iron for the brown part, because the iron-brown is apt to rot the fibre ; as once more you will see in some pieces of old tapestry or old Persian carpets, where the black is quite perished, or at least in the case of the carpet gone down to the knots. All intermediate shades can, as aforesaid, be got by the blending of these prime colours, or by using weak baths of them. For instance, all shades of flesh colour can be got by means of weak baths of madder and walnut M saddening " ; madder or cochineal mixed with weld gives us orange, and with saddening all imaginable shades between yellow and red, including the ambers, maize-colour, etc. The crimsons in Gothic tapestries must have been got by dyeing kermes over pale shades of blue, since the crimson red-dye, cochineal, had not yet come to Europe.
A word or two (entirely unscientific) about the processes of this old-fashioned or artistic dyeing.
In the first place, all dyes must be soluble colours, differing in this respect
■ from pigments; most of which are insoluble, and are only very finely divided, as, e.g., ultramarine, umber, terre-verte.
Next, dyes may be divided into those which need a mordant and those which do not; or, as the old chemist Bancroft very conveniently expresses it, into adjective and substantive dyes.
Indigo is the great substantive dye : the indigo has to be de-oxidised and thereby made soluble, in which state it loses its blue colour in proportion as the solution is complete ; the goods are plunged into this solution and worked in it " between two waters," as the phrase goes, and when exposed to the air the indigo they have got on them is swiftly oxidised, and once more becomes insoluble. This process is repeated till the required shade is got. All shades of blue can be got by this means, from the pale "watchet," as our forefathers called it, up to the blue which the eighteenth-century French dyers called " Bleu d'enfer." Navy Blue is the politer name for it to-day in England. I must add that, though this seems an easy process, the setting of the blue-vat is a ticklish job, and requires, I should say, more experience than any other dyeing process.
The brown dyes, walnut and catechu, need no mordant, and are substantive dyes; some of the yellows also can be dyed without mordant, but are much improved by it. The red dyes, kermes and madder, and the yellow dye weld, are especially mordant or adjective dyes : they are all dyed on an aluminous basis.
To put the matter plainly, the goods are worked in a solution of alum (usually with a little acid added), and after an interval of a day or two (ageing) are dyed in a bath of the dissolved dye-stuff.
A lake is thus formed on the fibre which is in most cases very durable. The effect of this " mordanting " of the fibre is clearest seen in the maddering of printed cotton goods, which are first printed with aluminous mordants of various degrees of strength (or with iron if black is needed, or a mixture of iron with alumina for purple), and then dyed wholesale in the madder-beck : the result being that the parts which have been mordanted come out various shades of red, etc., according to the strength or composition of the mordant, while the unmordanted parts remain a dirty pink, which has to be " cleared' into white by soaping and exposure to the sun and air ; which process both brightens and fixes the dyed parts.
Pliny saw this going on in Egypt, and it puzzled him very much, that a cloth dyed in one colour should come out coloured diversely.
That reminds me to say a word on the fish-dye of the ancients : it was a substantive dye and behaved somewhat as indigo. It was very permanent. The colour was a real purple in the modern sense of the word, i.e. a colour or shades of a colour between red and blue. The real Byzantine books which are written on purple vellum give you some, at least, of its shades. The ancients, you must remember, used words for colours in a way that seems vague to us, because they were generally thinking of the tone rather than the tint. When they wanted to specify a red dye they would not use the word purpureus, but coccineus, i.e. scarlet of kermes.
The art of dyeing, I am bound to say, is a difficult one, needing for its practice a good craftsman, with plenty of experience. Matching a colour by means of it is an agreeable but somewhat anxious game to play.
As to the artistic value of these dye-stuffs, most of which, together with the necessary mordant alumina, the world discovered in early times (I mean early historical times), I must tell you that they all make in their simplest forms beautiful colours ; they need no muddling into artistic usefulness, when you need your colours bright (as I hope you usually do), and they can be modified and toned without dirtying, as the foul blotches of the capitalist dyer cannot be. Like all dyes, they are not eternal; the sun in lighting them and beautifying them consumes them; yet gradually, and for the most part kindly, as (to use my example for the last time in this paper) you will see if you look at the Gothic tapestries in the drawing-room at Hampton Court. These colours in fading still remain beautiful, and never, even after long wear, pass into nothingness, through that stage of livid ugliness which distinguishes the commercial dyes as nuisances, even more than their short and by no means merry life.
I may also note that no textiles dyed blue or green, otherwise than by indigo, keep an agreeable colour by candle-light : many quite bright greens turning into sheer drab. A fashionable blue which simulates indigo turns into a slaty purple by candle-light; and Prussian blues are also much damaged by it. I except from this condemnation a commercial green known as gas-green, which is as abominable as its name, both by daylight and gaslight, and indeed one would almost expect it to make unlighted midnight hideous.