DYE

DYE

( 370 )

lower the heat with a little cold water, add apound more of vitriol, and return the cloth foran hour longer. The cloth is then walhed andaired again, and returned to the bath for anhour, after which it is well walhed in runningwater and fulled. It is laftly palled through ayellow bath of weld for a fhort time, to give ahigher glofs and foftnefs to the black. It isthen walhed and dried in the ufual manner.

The common blacks however are given in amuch Ampler manner, the Huff (previoufly dyedblue) being firft foaked in a bath of galls andboiled for two hours, and then palled throughanother bath of logwood and vitriol at a fcald-ing heat for as much longer, after which it iswalhed and fulled.

Several obfervations are to be made on thisprocefs.

The previous dyeing blue is not in the leaftneceflary to enable the cloth to take the blackafterwards, but it is found to be of great fervicein giving body to the colour, and is never omit-ted in the fineft blacks. The indigo blue is thebelt preparation for black, being a deep heavydye and affimilates well with perfect black.When this proves too expenlive for the Huff, itis fometimes prepared of a buff or fawn colourwith walnut hulks inftead of blue.

Black is never given by a (ingle operation: thatis, the fluff is firft impregnated with the galls orother aftringents either at once or elfe by feveralproceffes, and afterwards paffed into the vitriolbath. The colour is thus rendered much falterthan if the whole ingredients were firft mixed.A certain proportion mult be obferved betweenthe aftringent vegetables (of which kind are thegalls, logwood and fumach) and the fait of iron,for if the former are in too great a quantity, theblack is again degraded towards a grey ruftyhue. Too long a maceration of the cloth hasthe fame effedt, as Lewis has well obferved, dand Berthollet remarks that a rufty colour isgiven to the fineft black by being paffed througha frefh bath of galls. The black colour is notentirely brought out till after the cloth is ex-pofed to the air, an effedt fimilar to the well-known deepening of the colour of pale ink fomehours after it is ufed.

Logwood does more than merely add to thequantity of vegetable aftringent, for it con-tributes much to the depth of colour and coun-teracts the brownifh ruft tinge which galls andiron alone are apt to give. Where the cloth isnot previoufly blued, logwood is particularlyneceflary. A very fine black is produced on

* Commerce of the

blue cloth, according to Lewis, by 5 lb. ofvitriol, 5 lb. of galls, and 301b. of logwood.

The verdigris alfo has a good effect in im-proving the colour, but it is not exactly knownhow it a£ts.

In Hellot’s procefs the cloth already black isfinifhed by a yellow weld bath. Madder hasalfo been much ufed in the fame way, and isfuppofed to give a velvety foftnefs to the colour.The ufe of any of thefe finifhing tints is how-ever much difputed, and is in a good meafuredifcontinued.

Wool is dyed black nearly in the fame wayas woollen cloth. The natural greafe of thewool is firft removed by boiling in a bath offtale urine and water, after which the wool isdyed blue and black nearly in the w r ay above-mentioned.

Some variety of the above proceffes is re-quired to give a black dye to (ilk. Raw filk inthe ftate in which it is fpun from the coccoons,is covered with a natural kind of gum or var-nifh, which gives it its beautiful orange yellowcolour, and alfo a degree of ftiffnefs and elaf-ticity which is detrimental to the manufactureand muft be firft removed. This is done byboiling it in water for four or five hours with afifth of its weight of fine white foap which dif-folves this gummy matter. The filk lofes abouta fourth of its weight in this procefs. To dyeit black it is then boiled three or four hourswith about three-quarters of its weight of galls,and fuffered to remain without boiling for abouta day, more or lefs according to the kind ofmanufacture for which it is intended. It isthen blackened in a bath of fulphat of iron,iron filings, and cherry-tree gum, with manymanipulations too numerous to be here de-fcribed. Silk is feldom if ever previoufly blued,as wool is, but fometimes a root or fawn-colouredground is given by walnut hulks. Silk requiresmany more dippings and alternate foakings withgalls and iron than wool does, to produce a fullgood colour, and the quantity of galls requireddiffers moft remarkably, five or fix poundsbeing fufficient for a hundred pounds of wool,but upwards of fifty for the fame weight offilk. Hence the dyeing of filk is much moreexpenfive.

Hats are dyed with only a Angle bath of themixed ingredients. The bath is made of 100lb.of logwood, e 12 lb. of gum, and 6 lb. of gallsboiled for fome hours with water, after which61 b. of verdigris and 10 lb. of fulphat of ironare added, and the liquor kept juft of a fcaldingArts, * Lewis.