514 
E N A ME 
pounds of fea-falt, or muriat of foda, are added : the 
whole is well mixed together, and it is-fufed in the bot¬ 
tom of a furnace in which potter’s ware is baked. This 
matter is generally placed on fand, on lime quenched in 
the open air, or on allies. The bottom of the mafs is in 
general badly fufed. This, however, does not prevent 
the matter, after it has been pounded, and applied on 
the articles, from becoming exceedingly white and hard 
in tire furnace. This proccfs is that generally ufed in 
potteries. In the compofitions dellined for china-ware, 
the proportion of twenty-five parts of tin to one hundred 
of lead is" never exceeded : for common earthen-ware, 
the manufafhirers are even fatisfied with fifteen of tin to 
one hundred of lead. If it be wiflred to obtain an enamel 
whiter and more fufible, the quantity of fand mult be di- 
minilhed ; but there is no necefiity for augmenting that 
of the fea-falt, or muriat of foda, as the whitenefs and 
opacity depend on the quantity of tin. But it is necef- 
fary to employ fome further manipulations, when white 
enamel is required proper for being applied on metals, 
and to give all the perfection of which it is fufceptible. 
In that cafe the fand mult be calcined in a Itrong heat, 
with a quarter of its weight of marine l'alt, either in a 
fmall quantity in a crucible, or on a large fcale in a pot¬ 
ter’s furnace. If it be wilhed to have a very fufible ena¬ 
mel, add minium, or lead calcined by the former opera¬ 
tion, and nearly as much fea-falt; this produces a white 
mafs half fufed and porous, which is to be pulverifed and 
employed in the compofition of enamel inltead of fand, 
and in the fame proportions as fand. 
When it be wifiied to have fluxes for the colours, the 
fame compofitions may be employed, except that little 
or no tin is to be put into the lead. Nitre and borax are 
now generally ufed for making this glafs. The follow¬ 
ing are recommended as the belt, upon trial by C. 
Clouet; three parts of filiceous land, one of chalk, and 
three of calcined borax, give a matter .proper to be ufed 
as a flux for purples, blues, and other delicate colours. 
Three parts of white or flint glafs, one of calcined bo¬ 
rax, a quarter of a part of nitre, one of the. white Oxyd of 
antimony made with nitre well waflied, give an exceed¬ 
ingly white enamel, which may ferve alfo as a flux for 
purple, and particularly for blue. 
Sixty parts of enamel fand or lefs, thirty of alum, thir¬ 
ty-five of fea-falt, and a hundred of minium, or any other 
oxyd of lead, give a white enamel when the fluxes do 
not predominate too much, and a gelatinous glafs when a 
great deal of fluxes has been added. This glafs is good 
for red, and the enamel may be applied to all kinds of 
clay capable of fuftaining a ftrong heat. It is of great 
importance to remark, and to know, that the fand em¬ 
ployed for enamel muff not be fand which contains only 
fdex : fand of that kind alone is of no ufe. The fand 
proper for this purpofe is that which contains talc with 
filex. To make a fand proper for enamel and the fluxes 
of colours, there nihil be nearly one part of talc and 
three of filiceous fand. The principal quality of good 
enamel, and that which renders it fit for being applied on 
porcelaine, or on metals, is the facility with which it ac¬ 
quires lufire by a moderate heat, withqut entering into 
complete fufion. Enamels applied to thefe purpofes 
mull polfefs this quality. They do not enter into com¬ 
plete fufion ; they aflunie only the ftate of pafie, but of a 
palte exceedingly firm ; and yet when baked one might 
fay that they had been completely fufed. 
There are two methods of ornamenting or painting on 
enamel: on raw, or on baked, enamel. Both thefe me¬ 
thods are employed, or may be employed, for the fame 
objedl. Solid colours, capable of fuftaining the fire ne- 
ceflary for baking the enamel ground, may be applied in 
the form of tilled enamel on that which is raw, and the 
artifl may afterwards finifh with the tender colour's. The 
colours applied on the ratv material do not require any 
flux ; there is one, even, to which lilex mull be added, 
that is, the calx of copper, which gives a very beautiful 
s 
LLIN-G, 
green. All the colours'may be produced by the metallic 
oxyds. Thefe colours are more or lefs fufed iu the fire,, 
according as they adhere with more or lefs ftrength to- 
their oxygen. All metals which readily lofe their oxygen- 
cannot endure a great degree of heat, and are unfit for 
being employed on the raw material. 
Purple.— This colour is the oxyd of gold, which may 
be prepared different ways ; as by precipitating, by means 
of a muriatic folution of tin, a nitro-muriatic folution of 
gold much diluted in water. The lead quantity pofiible 
of the folution of tin will be fufficient to form this preci¬ 
pitate. The folution of tin mull be added gradually un¬ 
til the purple colour begins to appear: it is then put into 
an earthen veil'd to dry llovvly. But the colour is always 
more beautiful, if the precipitate is ground with the flux 
before it has become dry. The different folutions of 
gold, in whatever manner precipitated, provided the gold 
is precipitated in the ftate of an oxyd, give always a. 
purple colour, which will be more beautiful in propor¬ 
tion to the purity of the oxyd p but neither the copper 
nor filver, with which gold is generally found alloyed,, 
injure this colour in a fenfible manner: it is changed,, 
however, by iron. The gold precipitate which gives the 
mod beautiful purple is certainly fulminating gold, which' 
lofes that property when mixed with fluxes. Purple is 
an abundant colour ; it is capable of bearing a great deal 
of flux, and in a fmall quantity communicates its colour 
to a great deal of matter. It appears that faline fluxes 
are better fuited to it than thofe in which there are me¬ 
tallic calces. Thole, therefore, which have been made 
with filex, chalk, and borax, or white glafs, borax, and 
a little white oxyd of antimony, with a little nitre, ought 
to be employed with it. Purple will bear from four to 
twenty parts of flux, and even more, according to the 
fhade required. Painters in enamel employ generally for 
purple a flux which they call brilliant white. This flux- 
appeal's to be a femi-opake enamel, which has been drawn 
into tubes, and afterwards blown into a ball at an ena- 
meller’s lamp. Thefe bulbs are afterwards broken in 
Inch a manner that the flux is found in fmall feales, which, 
appear like the fragments of fmall hollow fpheres. Ena¬ 
mel painters mix this flux with a little nitre and borax. 
It is to be remarked, that purple will not bear a ftrong. 
heat. 
Red. —We have no metallic oxyd capable of giving 
diredlly a fufed red; that is to fay, we have no metallic 
calces which, entering into fufion, and combining under, 
the form of tranfparent glafs with fluxes or glafs, give 
diredlly a red colour. To obtain this, it mud be com¬ 
pounded different ways, as follows : Take two parts, or 
two parts and a half, of fulphat of iron and of fulphat of 
alumine; fufe them together in their water of cryftalli- 
fation, and mix them well together. Continue to Heat 
them to complete drynefs ; then increafe the fire fo as to 
bring the mixture to a red heat. The laft operation mull 
be performed in a reverberating furnace. Keep the,mix¬ 
ture to a red heat until it has every where affuined a beau¬ 
tiful red colour, which may be afeertained by taking out 
a little of it from time to time, and fullering it to cool in 
the air. The.red oxyds of iron give a red colour; but 
this is exceedingly fugitive : for, as foon as the oxyd of 
iron enters into fufion, the portion of oxygen which gives 
it its red colour leaves it, and it becomes black, yellow, 
or greenilh. To preferve, therefore, the red colour of 
this oxyd in the fife, it mull be prevented from vitrifying, 
and abandoning its oxygen. Clouet tried a variety ot" 
different fubflances to give it this fixity, but none of them 
fucceeded except alum. The doles of alum and fulphat 
of iron may be varied.. The more alum, the paler will 
be the colour. Three parts of alum to one of fulphat of 
iron give a flefh colour. It is alum alfo which gives this 
colour the property of becoming fixed at a very ftrong 
heat. This colour may be employed on raw enamel : ic 
has much more fixity than the purple, but not fo much 
as the blue of cobalt. It may be waflied to carry off the 
iuperfiugus. 
