PIGMENT. 
429 
brown, )ie fays, that the material from which the fame is 
to be made, is the (lime of fulphureous copper ore; and 
that the fame is to be taken to a furnace, commonly 
called a reverberatory-furnace, and calcined for about 
eight hours, with a ftrong fire conveyed over the top of 
it, at the end of which time the colour will be changed 
from a dark lead-colour to a dark chocolate-colour; in 
which ftate it mull be drawn from the furnace, and, when 
cold, muft be ground by a mill or other machine, being 
duly mixed .with water. After which it muft bg conveyed 
from the mill or machine, by a plug, into fpouts which 
remove it to fieves, and thence received into cifterns which 
communicate one with another, as defcribed in a former 
procefs ; and, after having ftood about twenty-four hours, 
the water is to be drawn from if, and the colour collect¬ 
ed and dried by fire, or otherwife, and then powdered 
for fale. 
Laftiy, With regard to the making or manufacturing 
of the paint or colour • called blue purple, or dark 
purple brown, the fame is to be made from the aforefaid 
dime of fulphureous copper ore; and muft be calcined in 
a reverberatory-furnace, for about fix hours; and, when 
cold, conveyed to a mill or machine, with a ftone on edge, 
where it muft be powdered. After which it muft be 
brought back to the furnace, and expofed a fecond time, 
for about fixteen hours, to a ftrong fire conveyed over the 
top of the colour; at the end of which time the colour 
will be changed to a bright blue purple colour, or by home 
called dark purple brown; in which ftate it muft be 
drawn from the furnace, and, when cold, ground, and 
conveyed and received into cifterns or veffels, in like 
manner as before mentioned ; and, after having ftood 
about twenty-four hours, the water muft be drawn from 
it, and the colour colledled, and dried by fire, or other- 
wife, and then powdered for fale. Rep. of Arts , vol. v. 
A dark-brown pigment has been colleded from the 
eyes of oxen and calves, by Leopold Gmelin, (Schweig- 
ger’s Journal, vol. x. p. 507.) From 500 eyes of oxen 
and calves he collected 75 grains of this fubftance. Its 
colour is blackifh brown. It is taftelefs, and adheres to 
the tongue like clay. It is infoluble in water, alcohol, 
fulphuric ether, oils, lime-water, and diddled vinegar. 
It diflolves in potafh and ammonia by the afiiftance of 
heat, and is again precipitated by acids. Sulphuric acid 
diflolves it and blackens the colour. Muriatic acid pro¬ 
duces the fame change of colour; but forms only an im¬ 
perfect folution. Nitric acid diflolves it, and changes its 
colour to reddilh-brown. 12^ grains (12^ Troy grains) 
of the pigment were fubjefted to heat in a'glafs tube; a 
few drops of water came over, holding carbonate of am¬ 
monia in folution, a brown oil, and cryftals of carbonate 
of ammonia. The gas extricated amounted to fix cubic 
inches. The water, oil, and carbonate of ammonia 
that came over into the receiver, weighed five grains ; and 
the oil alone amounted to one-third of the w-eight of the 
whole. The coal remaining in the retort weighed 5! 
grains. It confifted almoft entirely of charcoal. Gme¬ 
lin conceives that this pigment approaches the nature of 
indigo. 
Some experiments on the ink of the cuttle-fjh were pub- 
1 j filed in 1813 by Mr. Grover Kemp. Dr.'Prout lately 
analyzed a quantity of it in a dry ftate, which had been 
lent him in the original cyft in which it was contained. 
He found 100 parts of it to contain 78 of black colouring- 
matter. Leopold Gmelin particularly examined this co¬ 
louring matter, and found it to poflefs very nearly the 
fame properties with the black pigment of the human 
eye. (Sch weigger’s Journal, p. 533 .) His experiments 
do not quite agree with thole ftated by Dr. Prout; pro¬ 
bably, becaufe they were made upon the recent and moift 
pigment, whereas Dr. Prout’s experiments were made 
upon it in a dry ftate. 
Dr. Lewis acquaints us, that by mixing different blue, 
red, and yellow, colours, he has not been able to produce 
a perfedt black; but has often obtained from them very 
Vol. XX. No. 1380. 7 
dark colours, fuch as may be called brown olaelts, or grey - 
blacks; fuch as wecommonly fee in the dark parts of paint¬ 
ings, and fuch as the charcoal and foot-blacks appear 
when diluted a little. The ingredients being each of a 
dark deep colour is a very neceflary condition; for 
bright blues, bright reds, and bright yellows, mixed in 
fuch proportions that neither colour prevailed, produced 
only a grey. In effiedf,-fill compofitions of this kind, 
phylically confidered, can be no other than greys, or 
i'ome of the intermediate tints between whitenefs and 
darknefs; and thefe greys will be fo much,the lighter or 
darker as the component colours of themfelves are bright 
or dark. 
With regard to the extradition of the colouring matter 
from the different kinds of vegetables commonly to be 
met with of all colours, this would certainly be a very 
valuable acquifition, could the colours fo procured be 
made durable. But upon this fubjedt fee the article 
Dying, vol. vi. Seealfo the articles Enamelling, Glass, 
and Painting . 
Colours for the ufe of painters, paper-ftainers, See. are 
prepared, in the large way, by grinding them, either with 
oil or water, in mills worked formerly by horfes, but now 
frequently fleam-engines are ufed for fuch purpofe in 
London. Thefe colour-mills coniift of a large toothed 
wheel, or cog-wheel, which gives motion to feveral trun¬ 
dles and upright Ipindles of fmall mill-ltones placed round 
its circumference.. The conftruftion and ufe of thefe wiil 
be readily comprehended from the following defeription 
of a Angle pair of ftones to be worked by hand. See the 
annexed Plate, fig. 1. The winch-handle A gives mo¬ 
tion, by the labour of a man, to the fpindle B, and fly¬ 
wheel C, fixed thereon ; and which alfo carries a fmall 
fpur-wheel D, having eighteen bevelled teeth, which 
work into thofe of the crown-wheel E, of twenty-fix 
teeth, fixed upon the upright fpindle F, working in a 
brafs collar at top, fixed to the piece of wood G, which 
is adjuftable by means of the wedge H, fo as to keep the 
teeth of the wheels properly in gear; the bottom of the 
fpindle works in the end of the brafs ferew R, which 
works in the bottom framing of the machine, and pafles 
up through the centre of the lower ftone; the turning 
of which ferew, occafionally, adjufts the diftance of the 
ftones, which are of the common conftruction, exactly 
like thofe for grinding flour, but fmaller, each being fix* 
teen inches diameter and three inches thick. The up¬ 
per ftone I, is 1 'upported on the upright fpindle F by a 
fhoulder and crow, the fame as mill-ftones in general ; it 
has a hopper K affixed to it, and which revolves with it, 
into which the femi-fluid colours intended to be ground 
are put, and when ground they are protruded through a 
fpout from the tub MM, nineteen inches diameter, which 
contains the ftones. 
After the above procefs, colours for the ufe of paint¬ 
ers, &c. were ground by hand with oil or water, on a pc- 
liflied marble flab with a pebble muller; but, this procefs 
being tedious and expenfive, as well as highly, prejudicial 
to the health of the workmen, Mr. James Rawlinfon of 
Derby, fame years ago, contrived a mill for this purpofe, 
■which is reprefented at fig. 2. a model of which he pre- 
fented to the Society of Arts in the Adeiphi, London, in 
1804, an d for which they voted him the filver medal and 
ten guineas. A is a roller or cylinder of black marble, 
truly formed and well poliflied, t6 | inches diameter and 
4g inches broad; B is a concave muller, covering one- 
third of the roller, of the fame kind of marble, well 
polifhed, and fixed in the wooden cafe b, which is hung to 
the frame E at i i. C is a piece of iron, about an inch 
broad, to keep the muller fteady, and is fixed to the frame 
with a joint at f. The fmall binding-ferew, with the flv- 
nut, that pafles through the centre of the iron plate at c, 
is for the purpofe of laying more preffure on the muller, 
if required, as well as to keep it fteady. D is a taker- 
off, made of a clock-fpring about half an inch broad, and 
fixed fimilar to a frame-faw in an iron frame K, in an in- 
5 R dined 
