As there is an infinite variety of greys, without any positive names, produced by the same methods, it would be endless to enter into details, which would prolong this treatise to little purpose.
For reddish-grey the archil should predominate; for those more grey, the logwood; and for those rather greenish, the fustic.
Care should be taken not to use the logwood too much, as with the sulphate of iron it darkens more than most drugs: therefore the black vat, made either with alder-bark, or the other preparation mentioned in dyeing cotton, is preferable to the sulphate of iron.
NUT-GREY.
The fustic decoction, archil, and a little logwood are put into water moderately hot, the silk is then returned, and when the liquor is exhausted, the silk is taken out, and to soften the colour the solution of sulphate of iron, or the black vat, is used. The silk is then returned once more, and if the colour does not appear sufficiently even, some red spots still remaining, it may be concluded that it requires a little more sulphate of iron.
Observe that, as sulphate of iron is the general base of all greys, if this be deficient in quantity, the colour is apt to change in dyeing, and to become rough and uneven.
To know whether the colour be sufficiently softened, it should be examined, and if it wet easily, after having been wrung on the peg, it wants sulphate of iron. On the contrary, if it wets with a little difficulty, the colour is sufficiently softened.
Too much sulphate of iron stiffens the silk considerably, making it harsh, and even depriving it of a part of its lustre; to remedy this it must be extra washed and wrung at the peg; this process carries off the sulphate of iron.
BLACK-GREYS.
These are alumed and welded as for yellow, and, when the liquor is exhausted, part of it is thrown away, and some logwood is added; when the logwood is exhausted, sulphate of iron is added, sufficient to blacken the colour, the silk is then washed, wrung, and finished in the usual way.