C 403 ]

made harmless. The experiments in the foregoing sectionhave thewn, that about equal parts of galls and vitriolproduce the full blackness on paper; and our dyers, sofar as I can find, have generally employed the galls in aproportion not less than this, or at least; supplied theirdeficiency by a quantity of other astringents equivalent invirtue; from whence it should follow, that the commonblack dye cannot hurt the cloth. In this point I have notmyself had any fair experience, but am assured by a skil-ful and judicious dyer, that black, properly dyed, has byno means the corrosive quality generally attributed to it;and that the rottenness or perishableness, often complainedof in black cloths, &c. proceeds only from the cloth have-ing been damaged before the dying, for black is the dyecommonly had recourse to for damaged and unsaleablepieces, and such as have been spoilt in other dyes. Thoughvitriol, however mortified, be admitted to weaken thecloth, it is pretty clear that black is not the dye whichweakens it most ; for vitriol is used for some coffee colours,not indeed with quite so great a heat but in greater quan-tity than for the black dye itself; and the aquafortis em-ployed in scarlets, oranges, and some other colours, iscertainly more corrosive.

3. For dying black, especially on superfine cloths, it iscustomary to give a previous ground of some other deepcolour; and blue is preferred for this ground, as being oneof the most innocent dyes in regard to the cloth, and asbeing of all colours that which has the nearest affinity toblack : common black ink, and the black liquor of thedyer, when diluted largely with spring water, appear blue,as if their blackness was no other than a concentratedblue. The use assigned for this blue ground by the wri-ters on dying is, that the cloth, having already a consider-able body of colour, may require less of the blackening

Ggg materials,