148 
D Y I N 0. 
which the colouring particles may fuffer from the com- 
buftion that may be produced by the intermedium. 
Aftringents do not derive their characteridie prdperty 
from an acid, or from any other individual principle 
which is always the fame, but from the property which 
they potfefs of uniting with the calx of iron, of re¬ 
ducing it to the date of black calx, and of acquiring 
themfelves a dark colour, by the combuftion they 
undergo. Tan or galls, which.are to be confidered as 
the reprefentatives of all aftringents, readily undergo a 
flight combuftion, which gives them a deep brown co¬ 
lour; but this combuftion, which requires but a fnutll 
quantity of vital air, foon ceafes without injuring their 
properties. Galls owe their (lability to the large pro¬ 
portion of charcoal they contain ; and as they have the 
property of combining with fonie vegetable fubftances, 
with feveral colouring matters, and particularly with 
animal fubftances, they ferve as intermedium for them, 
and impart to them their own firmnefs of colour. For 
more on the chemical properties of mordants, and for 
an explanation of the modern chemical terms in dying, 
fee the article Chemistry, vol. iv. p. 14.8—343. 
Of DYING WOOL, and WOOLLEN GOODS. 
The value of wool, and its titnefs for the different 
kinds of manufacture, depend on the length and finenefs 
of its fibres. Thefe fibres poffefs a considerable degree 
of elallicity, but are by no means fmooth. Their external 
conformation appears to be made up either of f'mall 
lamina placed over each other, in a flaming direction, 
from the root towards the end or point of each fibre, 
like the feales of fifh, lying one over the other, in 
fucceftion, from the head to the tail; or of zones, placed 
one upon another, as in the horns of animals; from 
w hich ftruCture each fibre, if drawn from its root towards 
the point, will pafs fmoothly through the fingers; but 
if it be drawn in a contrary direction, from the point 
towards the root, a fenfible refiftance, and tremulous 
motion, will be felt by the fingers. This conformation 
difpofes the fibres of wool to catch hold of each other, 
and as they cannot recede, when aCted upon by other 
bodies, they naturally advance, by a progreftive motion, 
towards and befide each other, from the end towards 
the root : a difpofition which is very inconvenient to 
fpinning, and therefore the wool is greafed, that the 
afperities arifing from this ftruCture of its fibres may be 
thereby covered, or Iheatbed, as a covering of oil fheaths 
thofe of a fine file. But the wool being manufactured, 
and the greafe no longer ufeful, it is removed by 
fcowering, not only for the fake of cleanlinefs, but that 
it may not fruftrate the procefs of dying. The cloth is 
therefore carried to the fulling mill, and there fubjeCted 
to the aCtion of large beetles, with fullers earth and 
water, by which the cloth is not only fcowered, but its 
fibres, in confequence of the ftruCture juft deferibed, 
being made to conjoin, and advance toward and befide 
each other, become Pnorter, and more clofely connected, 
or felted together, the warp and woof lofing in extent, 
but gaining proportionably in thicknefs. 
The lamina, or zones, above deferibed, afford many 
interftices in the fibres of wool, fuited to receive and 
contain the particles of colouring matters, when applied 
to them in the operation of dying ; but thefe interftices 
being Anall, and the fibres of the wool naturally elaf- 
tic, no colour can be conveyed into thefe cavities, until 
they are diluted by hot or boiling water ; whereas filk, 
cotton, and linen, are made to receive colours without 
heat, as permanently as with it. And this difference 
manifeftly arifes from the fmallnefs of the intcrfticqs in 
which the colouring particles are depofited in wool, and 
the elafticity of its fibres, which make it neceffary to 
dilate them by hot or boiling water; and as the colour¬ 
ing particles are only made to enter and depofit them¬ 
felves by an artificial dilatation, it follows that, when 
Shis ceafes, the filaments will again contract to their 
former fize, upon the colouring matters fo introduced, 
and hold them much more ftrongly than they are likely 
to be held in other fubftances whole interftices are larger 
enough to receive colouring particles without being 
dilated, and which, therefore, cannot be fuppofed ever 
to contract and comprefs them in the fame way : and 
tills difference, joined to the fuperior chemical attrac¬ 
tion of animal fibres for colouring matters, will fuffi- 
ciently explain why many colours dyed upon wool and 
hair, prove fo much more durable than upon cotton or 
linen. Wool, as is well known, is the hair of fheep, 
and differs from common hair merely in finenefs and 
foftnefs. It is naturally covered with a kind of oil, 
which would obftrutt the procefs of dying, and is there¬ 
fore to be removed, by what is called fcowering ; an 
operation fufficiently known. Wool, when dyed in the 
fleece, takes up much more colouring matter than when 
fpun, and much more than when wove into cloth. It 
is alfo more or lefs penetrated, according to the finenefs 
of its own texture, and the particular nature of the 
colouring matter with which it is dyed. The very 
coarfe wool taken from the thighs and tails of forne 
rams and fheep, being never made to receive colours 
without difficulty ; and indeed the very fineft cloth is 
never thoroughly dyed fcarlet, it being always found 
white within when cut. Wool taken from different 
breeds of fheep, in various countries, is naturally of 
different colours ; as white, yellow, reddifli, and black. 
Formerly all the flocks in Spain, excepting thofe of 
Andalufia, were of this laft colour, it having been pre¬ 
ferred f.-r wearing by the native Spaniards; and this 
natural brow’nifh black is even at this time manufadtured, 
and worn conftantly by foiue religious orders in Roman 
Catholic countries. The white wool, however, is now 
almoft univerfally preferred to every other, as being 
fufceptible of receiving better colours by dying, than 
any of thofe which are natural. Manufactures of wool, 
though fuperfluous to man in a ftate of nature, feem 
to be, of all others, the moft important in civilized 
fociety. 
Dyers ufually confider five colours as primary , or fmple, 
viz. blue, yellow, red, black, and brown; becaufe from 
thefe they foriin all their compound colours, and they are 
confequently the foundation of all their other proceffes. 
Of BLUE. 
The only colouring matters employed in dying blue 
are woad, and indigo : attempts, indeed, have been made 
to dye with pruffat of iron, but they have hitherto failed. 
The ifatis tinBoria, or vvoad, is a plant commonly culti¬ 
vated in this kingdom, and even found wild in many parts 
of England. Some perfons think that it was this plant 
with which the ancient Britons ftained their bodies, to 
make them appear terrible to their enemies. When ar¬ 
rived at maturity, this plant is cut down, wafhed, dried 
huffily in the fun, ground in a mill, placed in heaps, and 
allowed to ferment for a fortnight; then well mixed to¬ 
gether, formed into balls, which are piled upon each 
other, and expofed to the w’ind and fun. When it has 
continued for a fufficient time, the woad is allowed jo 
fall to a coarfe powder ; and in this ftate it is fold to the 
dyers. The ftrongeft kind of vvoad is called pafd. 
Indigo, is a blue, extracted from the indigofera tmBoria, 
and from feveral other fpecies of the fame genus of plants, 
which are cultivated in the Eaft and Weft Indies. When 
the indigofera has arrived at maturity, . it -is..cut a few 
inches above ground, placed in ftrata in aTarge veffel, 
and covered with water. The plants foon acquire heat, 
ferment, and difeharge abundance of carbonic acid gas. 
When the fermentation is far enough advanced, the li¬ 
quid, now of a green colour, is decanted into large flat 
veffels, where it is conftantly agitated till blue flocculae 
begin to make their appearance. Lime water is now 
poured in, which caufes the blue flocks to precipitate. 
The colourlefs liquid is decanted off, and the blue fedi- 
ment 
r 
