254 
PLERAMIC STUDIO 
Pottery, German-Nuremburg, XVI Century — Faience Jog, Pewter Lid 
The property of the Metropolitan Museum, New York', 
The decoration over raw glaze is, from an artistic stand- 
point, far superior to the decoration over a fired glaze. 
In the decoration over raw, the colors applied over the 
glaze are not themselves vitrified, as they are infusible at 
the temperature at which the glaze matures. They owe 
their brilliant tone to the following phenomenon : when the 
glaze is vitrified under the action of heat, it becomes partly 
liquified and the colors penetrate it, superficially, it is true, 
but sufficiently to be thoroughly incorporated with it. In 
fact the glaze absorbs the color, but the latter is in such a 
small quantity that it does not materially affect the fusing 
point. 
In the decoration over raw glaze, color and glaze are 
then fired simultaneously, in the same firing. That is 
what is called "grand feu decoration of tin glazes," by op- 
position to the low fire decoration of which I will speak later 
on. 
This method of grand feu decoration is remarkable 
because the tones thus obtained have a softness which the 
vitrifying colors of the low muffle firing never have. 
The decoration is technically difficult because the raw 
glaze being easily scratched or rubbed off, no retouching is 
possible if a mistake has been made in the design or in the 
application of colors. This is quite different, as everybody 
knows, from the decoration over a fired glaze which has a 
hard, resisting surface. 
The beauty of the decoration over raw glaze depends 
entirely on the quality of the glaze, consequently on its 
composition and preparation. In this study of the prepara- 
tion of glazes and colors I will mention first the processes 
used in the XVI Century, then those which are in use at 
present. 
White Glaze. — The opaque tin white glaze is essentially 
constituted by a silicate of lead and tin. The tin, which 
makes the glaze opaque, may be introduced in two ways : i — 
In the shape of oxide. 2 — In the shape of calcine, which is 
a combination of lead and tin in variable proportions, the 
degree of opacity depending on the quantity of tin in the 
glaze. 
It is absolutely necessary to use very pure tins, free 
from iron, copper, zinc, antimony and arsenic. The best 
tins in that respect are those which come from Malaisia and 
which are known under the name of the parts from which 
they come — Malacca, Bianca, Detroits — but they are very 
expensive. Industrial factories generally use the tin from 
Biliton (Malaisia) which is sufficiently pure and lower in 
price. 
I do not propose to describe here the preparation of 
tin oxide and calcine, which I have given in my book on 
"Industrial fabrication of glazes and ceramic colors," espe- 
cially as these products are easily obtained from dealers. 
In the XVI Century Italian ceramists knew the two 
processes of the preparation of tin oxide and calcine. In 
some factories the oxide was used and was simply mixed 
with a flux made of: 
Flint 72 1 . . . 
Carbonate of potash ... 28 j 
Then the glaze was made of : 
Flux 72 ) . . 
tv -j o ( mixed 
I in oxide 28 J 
At Urbino, a town famous for its beautiful faiences, 
the white was made of : 
ABC 
Flux 35 63 27 
Flint 35 ir 27 
Tin oxide 30 26 46 
The B formula is the most fusible, the C formula the least 
fusible. 
In the province of Venice they used mostly a calcine 
containing from 10 to 26% of tin (metal) and 90 to 74 parts 
of lead, but this glaze was not as opaque as that used in 
the province of La Marche, for instance, the calcine of which 
contained as much as 33% tin. However, in a general way, 
the white tin glazes of Italy did not contain more than 20% 
tin. 
When in the XVI Century the Italian ceramists brought 
their art to France the composition of the tin glaze was 
modified because some of the materials were not the same 
as those used in Italy. At Nevers, so well known for the 
beauty of its tin glaze, this glaze was made of: 
Pottery Dish, Italian, Venice, XVII Century 
The property of the Metropolitan Museum, New York 
