Enamels and enamelling; an introduction to the preparation and ...

170 ENAMELS AND ENAMELLING.
white heat, and the finished tubes are coated with tar whilst
still hot.
PLEISCHEL'S ENAMELS.
Pleischel of Vienna has for many years manufactured
enamelled ware coated with leadless enamel only, the com-
position of the masses which are also suitable for use on sheet-
iron articles being
as follows :
Silica 30 to 50 parts.
Flint 10 to 20
Kaolin . . . 10 to 20
Pipeclay
8 to 16
Chalk 6 to 10
Ground porcelain . 5 to 15 ,,
Boric acid 20 to 40
Saltpetre
6 to 10
Gypsum 2 to 5 ,,
Another of the same maker's formulae is :
Quartz
30 to 50 parts.
Granite . . 20 to 30
Borax 10 to 20
Glass 6 to 10
Magnesia
Felspar
10 to 15
5 to 20
Enamel soda 10 to 20
Lime 5 to 15 ,,
Barytes
2 to 8
Fluor spar . 3 to 10
These ingredients are prepared in very much the same
manner as that already described in these pages, by grinding,
mixing, fusing and re-grinding ; and the glaze is laid on as
thinly as possible. The proportions of the mixture depend
on the character of the raw materials and must be determined
by experiment, since* a granite that contains a large proportion
of quartz will require more soda than one that is richer in
felspar.