515 
ENAMELLING. 
fuperfluous (aline matter, but it may be employed alfo 
without edulcoration ; in that flate it is even more fixed 
and more beautiful.' It does not require much flux ; the 
flux belt fuited to it is compofed of alum, minium, ma¬ 
rine fait, and enamel fand. This flux mlift be com¬ 
pounded in fuch a manner as to render it fufficiently fufible 
for its objedt: from two to three parts of it are mixed 
with the colour. In general, three parts of flux are ufed 
for one of colour: but this dofe may, and ought to be, 
varied, according to the nature of the colour, and the 
(hade required. Red calx of iron alone, when it enters 
into fufion with glafs, gives a colour which feems to be 
black; but if it be diluted with a fufficient quantity of 
glafs, it at laft becomes of a tranfparent yellow. Thus, 
the colour really produced by calx of hon combined with 
glafs is a yellow colour, but which being accumulated 
becomes fo dark that it appears black. In the procefs 
above given for making the red colour, the oxyd of iron 
does not fufe : and this is the effential point; for, if this 
colour is carried in the fire to vitrification, it becomes 
black, or yellowifli, inftead of red, and difappears if the 
coat .be thin, and the oxyd of iron prefent be only in a 
frnall quantity. 
Yellow.— Though yellow may be obtained in a diredfc 
manner, yet compound yellows are preferred ; becaufe 
they are more certain in their effedf, and more eafily ap¬ 
plied, than the yellow.,which may be directly produced 
from filver. The compound yellows are obtained in con- 
fequence of the fame principles as the red colour of iron. 
For this purpofe metallic oxyds are employed, the vitri¬ 
fication of which mud be prevented by mixing with them 
other fubftances, fuch as refraftory earths, or metallic 
oxyds difficult to be fufed. The metallic calces which 
form the bafes of the yellow colours are generally thofe 
of lead ; as minium, the white caht of lead, or litharge, 
the white calx of antimony, called diaphoretic antimony : 
that called crocus metallorum is alfo employed. This 
regulus, pulverifed. and mixed with white oxyd, gives 
likewife a yellow. The following are the different com- 
pofitions ufed: one part of the white oxyd of antimony, 
one of the'white oxyd of lead (or two or three) ; thefe 
dofes are exceedingly variable; one part of alum, and 
one of fal-ammoniac. When thefe matters have been all 
pulverifed, and mixed well together, they are put in a 
veflel over a fire fufficient to fublimate and decompofe 
the fal-ammoniac ; and when the matter has aflumed a 
yellow colour, the operation is finiflied. This in the 
(hops is called Naples yellow. The calces of lead mixed 
in a frnall quantity either with filex oralumine, alfo with 
the pure calx of tin, exceedingly white, give likewife 
yellow's. One part of the oxyd of lead is added to two, 
three, or four, of the other fubftances above-mentioned. 
In thefe different compofitions, for yellow, we may life 
alfo oxyd of iron, either pure, or that kind which has 
been prepared with alum and vitriol of iron : thus diffe¬ 
rent (hades of yellow may be obtained. Yellows require 
fo little flux, that one or two parts, in general, to one of 
the colour, are fufficient; faline fluxes are improper for 
them, and efpecially thofe which contain nitre. They 
muff be ufed with fluxes compofed of enamel fand, oxyd 
of lead, and borax, without marine fait. A yellow may 
be obtained diredfly from filver; for which may be ufed 
fulphat of filver, or any oxyd of that metal mixed with 
alumine or filex, or with both, in equal quantities. The 
whole mult be gently heated until the yellow colour 
appear; and the matter is to be employed with the fluxes 
pointed out for yellows. Yellow of''filver, like purple, 
cannot endure a ftrong heat : a nitric folution of filver, 
precipitated by the ammoniaeal phofphat of foda, will 
obtain a yellow precipitate, which may-be ufed to paint- 
in that colour with fluxes, which ought then to be a 
little harder. 
Green. —This colour is obtained diredtly from the 
oxyd of copper. All the oxyds of copper are good : they 
require little flux, which mull not be too fufible j one 
part or two of flux will be fufficient for one oxyd. This 
colour agrees with all the fluxes, the faline as well as 
the metallic; which tends to vary a little the fliades. A 
-mixture of yellow and blue is alfo ufed to produce green. 
Thofe who paint figures or portraits-employ glafs com¬ 
pofed in this manner; but thofe who paint glazed vef- 
fels, either earthen-ware or porcelain, employ in general 
copper green. Independently of the beautiful green co¬ 
lour produced by oxydated copper, it produces alfo a 
very beautiful red ; but it is exceedingly fugitive. The 
oxyd of copper gives red only when it contains very little 
oxygen, and approaches near to the flute of a regulus. 
Notwithftanding the difficulty of employing this oxyd, a 
method has been found to (lain tranfparent glafs with 
different (hades of a very beautiful red colour by means 
of it. It is exceedingly difficult to make this colour 
well; but when it fucceeds, it has a great deal of fplen- 
dour. By employing the calx of copper alone for the 
proceffes above-mentioned, we obtain a red fimilar to the 
mod beautiful carmine. The calx of iron changes the 
red into vermilion, according to the quantity added. If 
we had certain procefles for making this colour, we fliould 
obtain all the (hades of red from pure red to orange, by 
ufing, in different proportions, the oxyd of copper with 
that of iron. The calx of copper fufes argil more eafily 
than filex ; the cafe is the fame with calx of ii;on. If we 
fufe two or three parts of argil with one of the oxyd of 
copper, and if the heat be fufficient, we obtain a very 
opake enamel, and of a vermilion red colour: the oxyd. 
of copper pafles from red to green through yellow ; fo 
that the'enamel of copper, which becomes red at a ffrong 
heat, may be yellow with a weaker heat. The fame effedl 
may be produced by deoxydating copper in different de¬ 
grees : this will be effected according as the heat is more 
or lefs intenfe. The above compolition might alfo be 
employed to give a vermilion red colour to porcelaine 
but the heat of the porcelaine furnace muft be of fufficient 
ftrength to produce the proper effeiff. 
Blue.— This colour is obtained from the oxyd of co¬ 
balt. It is the mod fixed of all colours, and becomes 
equally beautiful with a weak as with a ffrong heat. The 
blue produced by cobalt is more beautiful the purer it is, 
and the more it is oxydated. Arfenic does not hurt it. 
The faline fluxes which contain nitre are thofe beft fuited 
to it. But the flux which gives to cobalt blue the great- 
eft fplendour and beauty, is that compofed of white glafs 
(which contains no metallic calx), of borax, nitre, and 
diaphoretic antimony well wafhed. When this glafs is 
made for the purpofe of being employed as a flux for 
blue, we add lefs of the white oxyd of antimony ; a fixth, 
of the whole is fufficient. 
Violet.— Black calx of manganefe, employed with 
faline fluxes, gives a very beautiful violet. By varying-, 
the-fluxes, the ffiade of the colour may alfo be varied 
it is very fixed as long as it retains its oxygen. The oxyd 
of manganefe may produce different colours; but for that 
purpofe it will be neceffary to fix its oxygen in it in dif¬ 
ferent proportions. Thefe are all the colours obtained, 
from metals. From hence it is evident that fomething, 
ftill remains to be difcovered. We do not know what 
might be produced by the oxyds of platina, tungften, 
molybdena, and nickel: all thefe oxyds are ftill to be 
tried ; each of them muff produce a colour, and perhaps, 
red, which is obtained neither diredtly nor with facility 
from any of the metallic fubftances formerly known and 
hitherto employed. 
Thofe who paint on enamel, on earthen-ware, porce- 
laine, &c- nnift regulate the fufibility of the colours by 
the mod tender of thofe employed ; as, for example, the 
purple. When the degree which is beft fuited to purple 
has been found, the other lefs fufible colours may be fo 
regulated (by additions of flux,) when it is neceffary 
to fufe all the colours at the fame time, and at the fame 
degree of heat. We may paint alfo'in enamel without 
flux 5 but all the colours do not equally ftand the heat 
neceffary 
