424 
PIGMENT. 
Jour of logwood to a pretty good blue; and, in general, 
(olutions of this metal are friendly to blue colours. The 
efteCts of folutions of gold, liiver, and mercury, are not 
fo well known,- they feem to produce dark colours of no 
great beauty. The moll powerful folution, however, 
with regard to a great numberof colours, is that of tin, 
made in nitro-muriatic acid. Hence we may fee the fal¬ 
lacy of Delaval’s hypothecs concerning colours, that the 
lealt refrangible ones are produced by the moft dettfe me¬ 
tals; for tin, which has the lealt denfity of any metal, 
has yet, in a Itate of folution, the molt extraordinary ef¬ 
fects upon the lea ft refrangible colours as well as thofe 
that are molt fo. The colour of cochineal is changed by 
it into the moll beautiful fcarlet j a limilar change is made 
upon the colouring matter of gum-lac. Brazil-wood is 
made to yield a fine purplifh crimfon ; logwood, a beauti¬ 
ful dark purple ; turmeric, 1 uflic, weld, and all yellow- 
colouring woods and flowers, are made to communicate 
colours far more beautiful than can be got from them by 
any other method. The blue colour of the flowers of 
violets, eye-bright, iris, &c. are heightened fo as to 
equal, if not excel, the blue produced by a folution of 
copper in volatile alkali. In fhort, this folution feems 
to be of much more extenfive ufe in colour-making, 
when properly applied, than any thing hitherto thought 
of. It is nor, however, univerfally ferviceable. The 
colour of madder it totally dellroys, and likewife that of 
faf-flower, changing them both to a dull orange. It 
likewife fpoils the colour of archil ; and what is very re¬ 
markable, the fine red colour of tinCture of rofes made 
with fulphuric acid is by folution of tin changed to a 
dirty green. 
The molt important confideration in colour-making 
is to make choice of fuch materials as produce the molt 
durable colours ; and, if thefe can be produced, an ordi¬ 
nary colour from them is to be preferred to a bright one 
from thofe which fade fooner. In what the difference 
confills between the colours that fade and thofe which 
do not, is not known with any degree of certainty. 
From fomeappearances itwculd feem, that thofe fubltances 
which are molt remarkable for keeping their colour, 
contain a vifcous glutinous matter, fo combined with a 
refinous one as to be foluble both in water and alcohol. 
The moll durable red colour is prepared from gum-lac. 
This is very llrongly refinous, though at the fame time 
fo far glutinous, that the colouring matter can be ex¬ 
tracted from it by water. Next to gum-lac are madder- 
roots and cochineal. The madder is an exceedingly pe¬ 
netrating fubftance, infomuch that, when given to ani¬ 
mals along with their food, it tinges their bones of a 
deep red colour. Its colouring matter is foluble both in 
water and alcohol. Along with the pure red, however, 
there is in madder a kind of vifcous altringent fubftance, 
of a dark brown colour, w'hich feems to give the durabi¬ 
lity to the whole. The colouring matter of cochineal, 
though foluble both in water and alcohol, is very tena¬ 
cious and mucilaginous, in which it bears lome refetn- 
blance to the purpura of the ancients, which kept its 
colour exceedingly well. Where the colours are fugitive, 
the tinging fubftance feems to be too refinous or too mu¬ 
cilaginous. Thus the colours of brazil, turmeric, &c. 
are very refinous, efpecially the latter, infomuch that the 
colouring matter of turmeric can fcarcely be extracted by 
water. Both thefe are periftiable, though beautiful co¬ 
lours; and much more are the red, purple, and blue, 
flowers, commonly to be met with. Thefe feem to be 
entirely mucilaginous, without the leaft quantify of 
refinous matter. The yellow flowers are different, and 
in general keep their colour pretty well. Whether it 
would be poflible, by adding occalionally a proper quan¬ 
tity of gum or refin, to make the fugitive colours more 
durable, hath not yet been tried, but feems to have fotne 
probability. What tends a little to confirm this, is a 
procefs given by M. Hellot for imparting durability to 
the colour of brazil. It confifts only in letting decoCtions 
of the wood ftand forfome time in wooden calks till they 
grow ftale and ropy. Pieces of woollen cloth now dyed 
in the liquor acquired a colour fo durable, that they 
were not in the leaft altered by expofure to the air during 
four months in the winter feafon. Whether this change 
in the durability of the colour was eifefted.by the ropi- 
nefs following the fermentation, or by fomeother ca-ufe, or 
whether the experiment can be at all depended upon, 
mull be referred to future obfervation. 
Having thus coilefted all that can as yet be depended 
upon for eftablilhing a general theory of colour-making, 
we (hall now proceed to give an account of the different 
pigments generally to be met with in the colour-lhops. 
i. Black. —Thefe are lamp-black, ivory-black, blue- 
black, and Indian-ink. The firft is the fined of what are 
called the foot-blacks, and is more ufed than any other. 
Its preparation is described in the Svvedifh Tranfactions 
for the year 1754, as a procefs dependent on the making 
of common relin: the impure refinous juice collected 
from incifions made in pin® and fir trees is boiled down 
with a little water, and drained whillt hot through a bag; 
the dregs and pieces of bark left in the drainer are burnt 
in a low oven, from which the fmoke is conveyed through 
a long paflage into a fquare chamber, having an opening 
on the top on which is a large fack made of thin woollen 
duff: the foot, or lamp-black, concretes partly in the 
chamber, from whence it is fwept out once in two or 
three days, and partly in the fack, which is now and then 
gently (truck upon, both for (baking down the foot, and. 
for clearing the interftices betwixt the threads, fo as to 
procure afufficient draught of air through it. In this 
manner lamp-black is prepared at the turpentine-houfes 
in England, from the dregs and refufe of the relinous 
matters which are there manufactured. 
On this fubjecl Dr. Lewis has fome curious obferva- 
tions. “ The foot (fays he) arifingin common chimneys, 
from the more oily or refinous woods, as the fir and pine, 
is obferved to contain more diffoluble matter than that 
from the other woods.; and this diffoluble matter appear;, 
in the former, to be more of an oily or refinous nature 
than in the latter, alcohol extracting it mod powerfully 
from the one, and water from the other. The oilin’efs 
and folubiiity of the foot feeming therefore to depend on 
thofe of the fubjeCt it is made from, it has been thought 
that lamp-black mud poffefs thefe qualities in a greater 
degree than any kind of common loot. Neverthelefs, on 
examining feveral parcels of lamp-black, procured from 
different (hops, I could not find that it gave any tinCture 
at all, either to alcohol or to water. SuipeCting (otne 
mistake or fophiftication, or that the lamp-black had been 
burnt or charred, as it is to fit it for lome particular 
ufes, I prepared myfelf fome loot from linfeed oil, by 
hanging a large copper pan over the flame of a lamp to 
receive its fmoke. In this manner the more curious 
artifts prepare lamp-black for the nicer purpofes; and 
from this collection of it from the flame of a lamp, the 
pigment probably received its name. The foot (o pre¬ 
pared gave no tinCture either to water or to alcohol, any 
more than the common, lamp-black of the (hops. I tried 
different kinds of oily and refinous bodies with the fame 
refult; even the foots obtained from fish-oils and tallow 
did not appear to differ from thofe of the vegetable-oils, 
and refins. They were all of a finer colour than the 
lamp-black commonly fold. Some foot was collected in 
like manner from fir and other woods, by burning finall 
pieces of them (lowly under a copper pan. All the foots 
were of a deeper black colour than thofe obtained from 
the fame kinds of wood in a common chimney; and very 
little, if at all, inferior to thofe of the oils : they gave 
only a juft-difcernible tinCture to water and alcohol, 
while the foots of the chimney imparted a (Hong deep one 
to both. The foot of mineral bitumens', in this dole way 
of burning, appears to be of the fame qualities with tho(e 
of woods, oil, and refins: in fome parts of Germany, 
great quantities of good lamp-black are prepared (torn a 
kind 
