428 PIG M 
fialine quality, they are not very proper. A very curious 
method of procuring a beautiful tranfparent blue colour 
is by extracting tile colouring matter from Prufiian blue, 
by means of a caudic alkali. This, when laid upon 
paper, appears of a dirty brown colour; but, if walked 
over with a we^k folution of green vitriol, is inllantly 
changed to a molt beautiful blue. This feems to afford 
a method of procuring blue tranfparent colours of greater 
beauty than are ufually met with. 
The preparation of blue verditer is kept a fecret, and 
the belt chemids have been puzzled to find out the me¬ 
thod. The colour is exceedingly bright, and has a confi- 
derable tinge of green. A methbd of preparing a colour 
equally beautiful, and agreeing in all refpefts with what 
is fold in the fiiops, except that of efrerveicing with acids, 
we have found to be as follows: “Diffoive copper in 
drong cauftic alkali, until the liquid has afl'umed a very 
deep blue colour; and, the deeper this colour is, the 
finer will your verditer be. When the menltruum has 
dili'olved as much of the metal as it can take up, it is to 
be poured out into a broad and well-glazed earthen pan, 
held over a very gentle fire ; and, from the moment it is 
put on, the liquor is to be continually agitated with a 
wooden fpatula, fo that all may be heated as equally 
as poffible. The whole fecret confids in properly regula¬ 
ting the degree of heat; for, if it exceeds the due pro¬ 
portion ever fo little, the verditer will turn out of a dirty 
green. The proper degree is about 90 0 of Fahrenheit’s 
thermometer. In this gentle heat the alkali (lowly eva¬ 
porates; and, in proportion to its doing fo, the verditer 
falls to the bottom. After it is once formed, freed from 
the alkaline liquor, and dried, it can bear the efFufion of 
boiling water without the lead injury. Dr. Prieftley, in his 
fixth volume, takes notice, that a folution of copper in 
volatile alkali affords a blue precipitate by heat, but 
without taking notice of the requifites for its fuccefs. 
In making this preparation, it is necefi'ary to difi'olve cop¬ 
per in its metallic date ; for the folution of any oxyde 
will not yield a blue but a green colour. This colour is 
durable in water, but diffolves in oil, and has then all the 
inconveniences of verdigris above mentioned.” Ency. 
Brit. art. Colour-making. 
Smalt is glafs coloured with zaffre, a preparation from 
cobalt. It is commonly fo grofsly powdered, that it 
cannot be uled in painting; and its texture is fo hard, 
that it cannot eaiily be levigated. Its colour is exceed¬ 
ingly bright and durable; fo that when finely levigated 
it is ufed indead of ultramine. The mod proper mate¬ 
rials for levigating this fubdance feem to be the plates of 
M. Reaumur’s porcelain recommended by Dr. Lewis. 
Indigo is but little ufed in painting, either in oil or 
water, on account of the dulnefs of the colour. It re¬ 
quires no other preparation than being walked over. Its 
goodnefs is known by the darknefs and brigbtnefs of the 
colour. See Indigo tinftoria, vol. xi. p. 16, 17. 
8. Purple, —The only fimple colour of this kind ufed 
at prefent is colcothar of vitriol. A beautiful purple ( 
lake may be prepared from logwood by means of folution 
of tin ; but this method of preparing colours is very little 
known. Mr. Anderfon’s method of preparing the colco¬ 
thar of vitriol is as follows : Oxyde of iron mud be put 
into a reverberatory-furnace, and a very drong fire con¬ 
veyed over the top of it for about fixteen hours, when the 
fame will be changed from a yellow to a bright light 
purple; and in that date it mud be drawn from the 
furnace, and, when cold, mud be ground by a mill or 
other machine; being duly mixed with water. After 
which it mud be conveyed from the mill or machine, by 
a plug, into fpouts which remove it to fieves, and thence 
into ciderns or veffels which communicate one with ano¬ 
ther, as defcribed in the former procefs; and, after the 
fame has dood about twenty-four hours, the water mud 
be drawn from it, and the colour collefted aud dried in 
the air, or otherwife ; after which it may be powdered 
for fale. 
ENT. 
9. Brown. — The brown colours are bidre, brown- 
ochre, Cologne-earth, umber, and brown-pink. Under 
the word Bistre is given a procefs for making that 
colour, by infilling foot in water, pouring off the tinfture, 
and then evaporating it to an extraft; but Dr. Lewis is 
of opinion, with M. Landois in the French Encyclopedic, 
that the foot is either boiled in water, or ground with a 
little liquid of fome kind into a fmooth pa.de ; it is then 
diluted with more water, and after Handing for about 
half an hour, till the grofier fubdance of the foot has fet¬ 
tled, the liquor is poured off into another ved’el, and fet 
by for two or three days, that the finer parts may fail to 
the bottom, and this fine matter is the bidre. This is a 
very ufeful colour in water, being exceedingly fine, 
durable, and not apt to fpoil any other colours with 
which it is mixed. 
Brown-pink is the tinging part of fome vegetable of a 
yellow or orange colour, precipitated upon the earth of 
alum,cuttle-fiih bone, orfome fimilarcalcareous fubdance. 
When good, it is a concentrated yellow, which, as a 
pigment, is tranfparent in oil, gives the effeft of a dark 
colour, and ferves for deep fhades. There are many 
methods of preparing brown pink. One of the bed an.d 
mod common methods is the following: Take of the 
French berries, one pound; of fudic wood in chips, half 
a pound : and of pearl-adies, one pound. Boil them in 
a tin boiler, with a gallon and a half of water, for an hour; 
and then drain off the tinfture through flannel, while 
the duid is boiling hot. Having prepared in the mean 
time a folution of a pound and a half of alum, put it gra¬ 
dually to the tinfture, as long as an ebullition (hall ap¬ 
pear; walli the fediment, as in the preparation of lakes, 
(which fee, vol. xii. p. 27.) and, when it is brought, by 
filtering through paper with a linen cloth, to a proper 
confidence, dry it on boards in fquare pieces. Or, it 
may be made without the ufe of falts, by boiling two 
pounds of the berries in a gallon of water for two hours, 
and draining off the tinfture through dannel. In the mean 
time prepare a pound and a half of cuttle-filh bone, by 
levigating the foft inner part with water on a marble; 
add this to the tinfture, and evaporate them in balnea 
Marits till the matter becomes of a ft iff confidence : when 
the whole has been well mixed by grinding, let it be laid 
on boards to dry. The goodnefs of broivn-pink mud be 
judged of by its tranfparency, and force of colour, when 
mixed with oil; but its qualities of danding well, and 
not fattening in oil, in both which refpefts it is com¬ 
monly defective, can only be afcertained by trial and 
experience. 
For making the paint or colour called Spanijh brown, 
Mr. Anderfon direfts,that the heterogeneous part of the 
faid precipitated ochre, oxyde of iron, material or refi- 
duurn from the boiler, as defcribed in the former procefs 
for the making of Venetian red, be taken to a reverbera¬ 
tory-furnace, where it mud be calcined with a drong heat 
for about fix hours, together with a native ochre, com¬ 
monly called yellow ochre; and at the end of that time 
its colour will be changed from a yellow to a dark-red 
colour, in which date it is to be taken from the furnace, 
and, when cold, ground by a mill or machine ; regard 
being had to the colour being duly mixed with water. 
After which it mud be conveyed from the mill or ma¬ 
chine, by a plug about twelve inches from the bottom of 
the tub, into fpouts which carry it into fieves; whence 
it mud be received into ciderns or veflels which commu¬ 
nicate one with another by fpouts, or otherwife, as de¬ 
fcribed in the procefs with refpeft to the making of the 
Venetian red. And,after the fame has (food about twenty- 
four hours, the water mud be drawn from it, and the co¬ 
lour removed to a pan or receiver, or other vefl'el made 
of bricks or other materials, capable of bearing heat; and, 
after being dried by fire, or otherwife, mud be powdered 
for fale. 
With regard to the making or manufafturing of the 
paint or colour called chocolate purple brown , or purple 
brown # 
3 
