Printed for D. Wilson, and T. Durham, at Plato's Head, in the Strand. Lontoo, 1756
The ordinary greens, stained blue in a woad vat, and afterwards yellow, in a bath of dyer's woad, are seldom uniform, almost always dull, and require several days labour to finish them intirely.
The green, dyed according to the new process, of which the Saxons are believed to be the inventors, is, without comparison, more fresh and lively; and, in four and twenty hours, one may dye several pieces of cloth, first blue, and then green, in the same copper. Altho' this green is not so solid, when tried instantaneously, as the common green; nevertheless, it resists as much as these, both the action of the air, and the rays of the sun; and its lustre hath obtained it the preserence over them, in England, Germany, and the Northern countries.
The first Saxon greens imported into the kingdom were purchased immediately, and the public, astonished at their liveliness, was desirous that they should be imitated in France. Their desire was complied with, as soon as it was possible to learn the basis of the process; and those who were charged with the execution have succeeded so much to their wish, that the last cloth which they dyed are, at least, as pretty as the finest greens brought from Saxony.
The foundation of this green is a blue, extracted from indigo by the acid of vitriol: it is covered with a yellow, extracted from real yellow woad, from dyer's weed, or from any other in gredient, which gives a yellow of a good tint: but the success of the process depends upon the choice of the acid, known in trade by the appellation of oil of vitriol; and also upon the equal distribution of the same acid, when it is incorporated with the blue of indigo in the copper, where the cloth is to be dyed first a lively mining blue, and afterwards a yellow, which is to be changed into a green.
If the oil of vitriol is weakened by a too great quantity of aqueous particles, it doth not attack the best indigo, or, at least, extracts from it but an ugly grey.
If the indigo blue, extracted by a concentrated, or very acid oil of vitriol, is not equally distributed in the bath of the copper; as this liquor is much heavier than water, it is precipitated to the bottom by its own gravity: in this case, the cloth dipt in the bath imbibes the blue unequally, and appears variously shaded. It takes indeed the green colour in the bath of yellow; but that green is also differently shaded.
In publishing the process of a Saxon green, we thought proper to begin with informing dyers with the method of preventing these defects. The common oil of vitriol, which is bought of druggists, or brought from Hamburgh or Holland, must be concentrated by distillation. But this operation is difficult for a dyer, who is not supposed capable of conducting a distillation by a retort. Now it is required to have the oil of vitriol with the fewest aqueous particles possible; these may be expelled by a sand-fire, strong enough to make them evaporate into smoke or vapour. When the oil of vitriol ceases to smoke with the same degree of heat, it is a sure sign that it is concentrated, or acid enough to extract the blue colour from indigo, and consequently to make what is called in the process the composition. This evaporation is performed in a glass pot without a funnel, better than in any other vessel: where that is wanting, a well-burnt stone pot may be used, provided it is not porous; or, finally, an earthen pot well varnished, which, however, is not so proper for that operation, as either those of stone or of glass.
This vessel, of glass, of stone, or of varnished earth, is to be placed upon an iron pan, half, or two thirds, full of fine sand, which ought to be well dried before.
This iron pan must be put upon a stove, with a grate, and an ash-pan under it, and the bed of sand must be gradually heated with a charcoal fire, that the glass, stone, or earthen pot may likewise be heated by degrees, and not be in danger of cracking, which would certainly be the case, if it was warmed too quickly.
As soon as the oil of vitriol emits no more aqueous vapours, the acid begins to evaporate: it is easily judged if the vapour is acid by holding a piece of blue paper stretched over it: if the paper becomes red almost instantaneously, the liquor is sufficiently evaporated: allow it then to cool, till it be lukewarm, by taking the pot off the hot sand, and placing it upon straw at a small distance from the stone, that the contiguous air may be dry: for, was it placed in a moist air, the oil of vitriol would re-imbibe the aqueous humidity, which it lost by evaporation.
This liquor, being thus cooled, so as to be hardly luke warm, must be poured upon the quantity of indigo, which shall be afterward prescribed.
The indigo, however, must be beforehand reduced to a powder, and put into a glass or stone vessel, which should be well stopt with a cork, with wax round it, left the oil of vitriol, after dissolving the indigo, which is then called the composition of blue, should re-attract the moisture of the air.
In fine, if you would be absolutely certain that the oil of vitriol is concentrated enough not to fail in forming this composition, you have only to pour two ounces of it upon forty or fifty grains of pulverized indigo, put into a vial, and to mix them well by shaking the vial: in an hour's time, the liquor which floats above the sediment, should be of a fine dirk blue: if it is only grey, the oil of vitriol is not enough concentrated.
Process for dying a piece of cloth, twenty ells long, into a Saxon green.
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Dissolve in a sufficient quantity of river-water, which breaks soap persectly well, three pounds and a half of Roman allum, and two pounds of the powder of white tartar: boil the cloth in it half an hour, or, five and thirty minutes at most: take it out and expose it to the air to cool, but do not wash it.
Refresh the bath of this boiler with twenty or five and twenty buckets full of water, and throw in, at two disferent times, the composition of blue, designed for the cloth. If the oil of vitriol has concentrated, or has stood the proof which we shewed above, it is sufficient to take a pound and an half, and pour it lukewarm upon two ounces and an half of fine powder of indigo. You must wait till the dissolution is made, and the liquor becomes a fine dark blue: but if this composition of blue has been made some days before, so much the the better; For then you may take one pound ten ounces, or a little more, and pour the half of it into a pretty large stone pot, or into a bucket, proper for the use, into which there must be put before, ten or twelve pints of the refreshed bath from the boiler. The whole must be well jumbled, in order to diffuse the composition of blue. You must likewise have a straining bag of cloth, steep it well in the bath of the boiler, open it, and pour into it that half of the composition, which is already mixt. By this means you will preserve the straining-bag, which, without this precaution, would have been burnt by the oil of vitriol, if it had been poured in as much concentrated as at first.
Put the straining-tag over the whole extent of the bath, that it may imbibe the blue equally: palliate likewise the bath, that the distribution of the colouring particles may be more equal: when the cloth is cooled, let it down into the cauldron, and keep it there five or fix minutes without boiling, turning it rapidly, and agitating the bath with a pole of white woad. Then take out the cloth, raising it only upon the turn.
Put the straining-bag again into the same bath, and throw in the other half of the composition of blue, after it has been dissolved as the former half, in ten or twelve pints of water taken from the boiler. Pass the straining-bag over the bath, as formerly, palliate it strongly, let down the cloth, and turn it three or four times very quickly, in continuing to agitate the bath with the stick: in fine, in order to make the colour even, boil the bath of blue very gently, and turn the cloth in it slowly for seven or eight minutes. Take it out stained blue, and let it cool.
Empty this boiler of three-fourths of its contents, and as many buckets full as you take out of the blue bath, pour in the like number of the yellow bath, described below.
In order to make the yellow bath, you must heat gradually another boiler, into which must be put a sufficient quantity of pure river-water, with a bag of new coarse cloth, containing from ten to twelve pounds of real yellow woad (not fustic) cut into chips.
When this bath has been heated by degrees till it boil, you must let it boil two full hours.
Yellow woad, cut into chips, succeeds better than when it is ground; in this case, eight pounds are sufficient for a piece of cloth of twenty ells; but there is a great risque of using it adulterated.
After you have poured into the first boiler when the blue was made, the quantity of the yellow bath, prescribed above, or even a greater number of buckets full, according to the shade of green required; the blue cloths, which ought to be sufficiently cooled, must be let down into this new bath, when very hot; and stirred about till you have the shade of green you want: then take out the cloth, cool it by exposing it to the air, wash it, lay the nap, dry it on the tenterhooks, brush it, as scarlet is brushed, and afterwards press it, but in this operation, let it be as cool as possible.
If you have several pieces of blue cloth to be dyed green successively, you must take from the bath, which dyed the preceding piece blue, as many buckets full as are to be added from the yellow bath to dye the blue cloth into a green; which will amount to twenty buckets full, or thereabouts, to be taken out, and twenty to be supplied; by these means the shades of green are rendered more equal and uniform.
The Saxon green of that cloth, which hath been first dyed blue in a bath composed of allum and white tartar, is much more solid than of that which is stained blue in a new bath of plain water, without these salts; but it has not so good a lustre. However, as it resists the rays of the sun for twelve days, it may be reputed a very good tint. Being made by means of an acid, it must not be proved by soap, which is prescribed for the ordinary greens made in the blue vat.
In order to prove it, you should boil it for five minutes in a quart of water, with two drachms of Roman allum, as scarlet is tried, what is also dyed with an acid: if it preserves its colour, it may be reckoned a very good tint, although by this operation it loses much more than in the rays of the sun.
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