274 
RERAMIC STUDIO 
HOW TO MAKE COLORED ENAMELS. 
THE manufacture of colored enamels for decorating 
china, porcelain, glass and metal has become quite a 
flourishing industry in some of the important European glass 
making countries. Two kinds of enamels are manufactured, 
the opaque and the transparent, the former being produced 
from the latter by a simple addition of tin oxide. The oxides 
in the colored enamels are present in the form of silicates and 
borates, says the London Pottery Gazette. The melting tem- 
peratures of the different colorants vary considerably. It is 
higher with the real colored glass, whigh does not melt at 
less than about 1200 degrees, lower with the enamels for light 
glazings on porcelains, china or bisque. The melting points of 
these enamels lie between 850 and 900 degrees. Stdl lower 
is the melting temperature of these enamels which are des- 
tined for metals and glass painting proper, as they contain 
usually a very large quantitj^ of lead oxide. 
Easily fusible enamels are obtained by melting lead glass 
together with various metallic oxides, the number of which 
however is rather limited. Green is produced by copper 
oxide; manganese oxide alone furnishes violet; mixed with 
some iron oxide, brown; cobalt oxide is the basis for blue. 
Antimoniate of potash gives to the copper oxide green a yellow 
tint, but renders the mass slightly opaque. Black is obtained 
by mixing red iron oxide and the oxides of cobalt, copper and 
manganese. 
In Salvetat's book we find some recipes for transparent 
colored enamels which have proved very suitable for orna- 
menting porcelain bisque. As a base for colored transparent 
enamels, a glass is used which is composed of 100 parts quartz, 
50 borax and 200 red lead. 
Ivory colored enamel is obtained by melting together lOO 
quartz, 50 borax, 200 red lead, 3 antunoniate of potash, 6 
hydrated iron oxide and 3 carbonate of zinc. 
Yellow enamel: 100 quartz, 50 borax, 20 red lead, 2 chro- 
mate of potash. 
Violet enamel: 100 quartz, 50 borax, 200 red lead, 12 car- 
bonate of manganese. 
Blue enamel: 100 quartz, 50 borax, 200 red lead, 6 cobalt 
oxide. 
Green enamel: lOO quartz, 50 borax, 200 red lead, 10 
copper oxide. 
Yellow-brown enamel: 100 quartz, 50 borax, 200 red lead, 
40 red iron oxide. 
Black enamel: 100 quartz, 50 borax, 200 red lead, I co- 
balt oxide, I copper oxide, 3 manganese oxide, 2 red iron oxide 
In order to convert the transparent enamels into opaque 
enamels, there is, according to Steele, a suitable quantity of 
tin oxide added to the flux. As it is known that the enamels 
receive a certain degree of opaqueness if the tin contents 
are one-tenth of the whole weight, all that is needed to render 
an enamel opaque is to add the corresponding weight of tin 
oxide. Tliis is best done by mixing the tin oxide with the 
litharge, so that for producing opaque enamel, 106 parts of this 
mixture is put into the batch, instead of 100 parts litharge alone, 
as is done in the case of transparent enamel. 
The transparent enamels are used ita the painting of glass 
to put upon white glass at certain places a transparent colored 
covering. Such colored coverings, however, can also be pro- 
duced by another method, namely by impregnating. This is 
done by covering the glass surface with a mass which without 
forming a molten colored glass layer, colors the glass during 
buming-in, while the residuum serving as the vehicle, consist- 
ing of ferruginous clay oriron oxide, is removed at the end q\ the 
process . If both sides of a glass sheet are treated in this manner 
it has the appearance as if it were dyed in the batch. This 
method is chiefly used in the production of yellow by means of 
silver. This action of the metal on glass was discovered in the 
fourteenth century, and if today, instead of the metal, chloride 
of silver or silver oxide be used, it is done only because those 
substances can better be obtained in finest powder form than 
metallic silver, and are reduced to metal by the higli temper- 
ature in the muffle. Silver oxide, however, is to be preferred, 
as, owing to its easier reductibility, a lower temperature can be 
employed, and colors lower in metal can be produced, which 
means a saving in silver. 
The chloride of oxide of silver is not applied in its pure 
condition, but in combination with an indifferent material 
which, at the high temperature in the muffle, neither shritiks 
nor sinters, nor adlieres to the glass. Such a substance is clay, 
red chalk, or iron oxide, which, before use, have to be exposed 
for some length of time to a higher temperature. Assurance 
is hereby obtained that during the burn-in operation there is no 
shrinkage or cracking of the layer by which certain places of the 
glass would be exposed, and hence escape the coloring action of 
the metal. With one of the indifferent materials chloride of 
silver is mixed in the proportion of 10 to 15, oxide of silver in 
that of I to 15 or 20. Water is added to this mixture until the 
proper consistency is reached, when it is apphed to the glass in a 
moderately thin layer. After having dried at an ordinary tem- 
perature, the glass is put into the muffle, where it remains until 
the color is perfectly developed. The residuary mass on the 
glass is afterwards removed with brush and water. 
According to the content of the silver in the mass the glass 
is more or less strongly colored, but even when producing the 
deepest, richest yellow, there is generally 95 per cent of silver 
left, which can again be utilized after having been regener- 
ated into oxide, by means of nitric acid and caustic potash. 
The coloring given to glass by this method is purely super- 
ficial, and the thickness of the yellow layer can hardly be 
measured, but the process is easily accomplished and the result 
lasting. 
DESIGN OF FISH FKOM "ART ET DECORATION ' 
CARP-M. SBGUY 
