422 
PIGMENT. 
more or lefs poflefled of the colouring fuccus; this was, 
by means of a pair of fine-pointed fcifl'ars, extradled with 
as little of the adjoining flefh aspoffible, and ground on a 
piece of plate-glafs, with a few drops of fpring-water. 
Thus prepared of a proper confiftency, it was of a dull 
green colour, which it continued for a confiderable time 
in bulk ; but fome which was fpread thin changed to its 
ultimate colour in the courfe of the day, without the affift- 
ance of the fun, though we have found it continue many 
days in its.premature green, if light has been excluded. 
Some of this matter, when thoroughly dry, taken up by a 
hair-pencil dipped in water, and applied to linen, was by 
the affiftance of the folar rays fpeedily turned to dull pur¬ 
ple, and afterwards, by walking with foap, to a crimfon, 
not much inferior in colour to the recent dye, but never 
fo ftrong. Whether the colouring matter of this fpecies 
was ever ufed by the ancients, is to be doubted, fince fo 
fmall a quantity is produced by each animal.” 
We are informed that fome Spanifn philofopher difco- 
vered a fhell on the coaft of Guayaquil and Guatimala, in 
Peru, that produced a purple dye. All the defcription 
we have of this fhell is, that it is the fize of a walnut, and 
that the dye, fimilar to that of Buccinum lapillus, changes 
from white to green, and is not purple till dry; the me¬ 
thod however of extracting it clearly proves it to be very 
dj Hindi from that fpecies. The operation is performed 
either by killing and prefling the animal, or by drawing 
it partly out of the fhell and fqueezing, it is made to 
yield the fluid which ferves for dyeing; tliis is repeated 
four times at different intervals, but always with lefs fuc- 
cefs. If continued, the animal dies. No colour at pre- 
icnt known, fays the Abbe Raynal, can be compared to 
this, either as to iu ft re, livelinefs, or duration. 
M. Stroem, a Norwegian clergyman, who fludied with 
nffiduity the natural produdlions of hiscountry, publifhed 
(if.we rightly recolleff) a diflertation on the Buccinum 
lapillus; in which, among other interefting particu¬ 
lars, he endeavoured to prove that the fine purple dye 
was procured from the uterine humours of the animal in¬ 
habitant. That a liquid fecretion, capable of communi¬ 
cating a purple tinge, may. exift in the womb as weil as in 
a particular vein of the fame animal, implies no contra- 
didlion, and, if the Hydratriticea of Linnaeus be, as is 
now generally alleged, the ovary of the creature in quef- 
tion, its contained juice, as we have known fince the 
days of Reaumur, imparts a fine purple ftain to linen. 
The colouring matter obtained from the animal of the 
Turbo clathrus may be perceived in the form of a beauti¬ 
ful, purple liquor, which is difcharged by allowing the 
animal to ficken in confequence of being kept for fome 
days in fea-water. This circumftance, which is noted by 
Plancus and Martini, tends to confirm the conjedlure 
that it may have contributed to the celebrated Tyrian 
dye.. Indeed it appears much more probable that the co¬ 
louring fecretion of this animal fliould have attracted no¬ 
tice, and have been coliedled as a dye, than that of the 
Buccinum lapillus, for the obvious reafon, that it not 
only produces the fluid fpontaneoufly, and in much 
greater quantity, but that its primitive colour is of that 
richnefs fo glowingly defcribed. Murex Brandaris, called 
by Rondeletius Murex purpura, is generally believed to 
be one of the fpecies that afforded that coftly dye in the 
Mediterranean. The Jhell, which in Englifh has been 
called the thorny fnipe’s head, is figured on the Concho- 
logy Plate XIII. fig. 8. and others of the fame tribe, 
for there are feveral varieties, at figs, a, 3, 4, of Plate 
XIX. 
But, while we are enquiring thus minutely into the pig¬ 
ments ufed by the ancients, we are juftly reproached, by 
a correfpondent at Stockton-upon-Tees, with having to¬ 
tally omitted, under our article Colour, to defcribe the 
modern art of Colour-making. Though the work was 
in different hands at the time that article was printed, it 
behoves us no lefs to fupply the deficiencies of ourprede- 
ceflor. 
The principles on which colour-making depends arc 
entirely different from thofe on which the theory of other 
parts of chemiftry is founded ; and, the pradlical part be¬ 
ing in the hands of thofe who find it their intereft to 
conceal their methods as much as poflible, it thence hap¬ 
pens, that no diftindl theory of this art has ever yet ap¬ 
peared in print. 
The more general divifion of colours is into opaque and 
transparent. By the firft are meant fuch colours as, when 
laid over paper, wood, &c. cover them fully, fo as to ef¬ 
face any other painting or ftain that might have been 
there before; the others are of fuch a nature as to leave 
the ground on which they are laid vifible through them. 
Of the firft kind are white-lead, red-lead, vermilion, &c. 
of the latter kind are the colours ufed for illuminating 
maps, &c. 
Another divifion is into oil-colours and water-colours; 
by which is meant fuch as are appropriated to painting in 
oil and in water. Moft of thofe which are proper for 
painting in water, are alfo proper for being ufed" in oil. 
There is, however, this remarkable difference betwixt 
colours when mixed with water and with oil, that fuch 
as are quite opaque in water will become perfedlly tranf- 
parent in oil. Thus, blue verditer, though exceedingly 
opaque in water, if ground with oil, feems totally to dif- 
folve, and will become very tranfparent. The fame thing 
happens to fuch colours as have for their bafis the oxyde 
of tin, alabafter, or calcareous earth. The moft per- 
feflly opaque colours in oil are fuch as have lead, mer¬ 
cury, or iron, for their bafis : to the latter, however, Pruf- 
fian blue is an exception ; for, though the bafis of that 
colour is iron, it proves quite tranfparent when ground 
with oil. In'water-colours, thofe prepared from metals, 
Pruflian blue alone excepted, are always opaque; from 
vegetables or animals, tranfparent. Coal, however, 
whether vegetable or animal, is opaque both in water 
and oil. 
Colours, again, may be confidered as either Jimple or 
compound. The fimple ones are fuch as require nothing 
to be fuperadded to them, in order to make a full ftrong 
colour, without regarding whether they are formed of 
many or few ingredients; and in this view, white-lead, 
red-lead, vermilion, oxydes of iron, See. are fimple co¬ 
lours. The compound ones are formed by the union of 
two or more colouring fubftances; as blue and yellow 
united together to form a green, red and yellow to form 
an orange, a white earth or oxyde with the red colour 
of cochineal or brazil to form a lake, &c. and thus car¬ 
mine, lake, rofe-pink, Dutch-pink, Engiifli-pink, &c. are 
compound colours. 
The laft and moft important divifion of colours is inlo 
true and falfe. By the former are meant thofe which re¬ 
tain their colour under every poflible variety of circum- 
ftances, without fading in the leaft; the others are fuch 
as do not; but either lofe their colour altogether, or 
change to fome other. What is chiefly apt to affedl co¬ 
lours, is their being expofed to the fun in fummer, and 
to the cold air in winter: but to this there is one excep¬ 
tion, viz. white-lead; which, when ground with oil, re¬ 
tains its whitenefs if expofed to the weather, but degene¬ 
rates into a brownilh or yellovvifti colour if clofe kept. 
In water this fubftance is very apt to lofe its colour, whe¬ 
ther expofed to the air or nor. The great defideratum in 
colour-making is to produce the firft kind of colours, viz. 
fuch as will not fade by expofure to the weather; and in¬ 
deed it is to be regretted, that the moft beautiful are in 
general the leaft permanent. It may, for the moft part, 
however, be expedled, that the more fimple any colour 
is, the lefs liable will it be to change upon expofure to 
the air. 
The great difficulty of knowing a priori whether a co¬ 
lour will fade or not, is owing to our ignorance concern¬ 
ing the nature of colouring fubftances. With all our 
disadvantages, however, we may obferve, that whatever 
change of colour is produced in any fubftance by expo¬ 
fure 
