256 
KOVAMIC STUDIO 
Spain, Alcora, XVIII Century — Plate, Entry of Alexander into Babylon 
The property of the Metropolitan Museum, New York 
Sand of Decize 50 \ 
j sulphate of potash / 
Alkaline salts -I sulphate of soda 13' fritted 
( carbonate of potash / 
Calcine made of 17% tin, 83% lead 30 \ 
Limaille d'epingles 0,252 / 
Limaille d'epingles was copper scales, the shavings left 
from the fabrication of pins which were made of copper. 
For the first time the sand of Decize appears in the com- 
position of the white glaze. Decize is a place near Nevers, 
where there is a rich bed of feldspathic sand. The Nevers 
potters, having no other sand at hand, used it without 
realizing that it had very remarkable properties. When 
introduced into a glaze it gives it a kind of elasticity which 
allows this glaze to fit many different clays without creasing. 
Since that time this sand has been commonly used for 
faience glazes. 
Here is its chemical constitution which I give in the 
hope that similar sands may be found in America: 
Silica 86,12 
Alumina 8,52 
Iron oxide 0,12 
Lime 0,13 
Potash 2,24 
Soda 0,22 
Water 2,60 
It then corresponds to a mixture of 
Feldspar 45 
Flint 55 
I must also explain that limaille d'epingles or copper 
scales were used in the Nevers glaze to give it a slightly 
bluish tint, which would make it appear whiter. This 
would have been the case if the glaze had contained a large 
quantity of alkaline salts (potash and soda), but in reality, 
instead of being tinted blue, it was tinted green, a very 
light tint, but often easily detected. At present we use 
cobalt oxide instead of copper. 
There are two formulas of white tin glaze used to-day. 
One is based on the feldspathic sand of Decize, the other 
on flint or quartzy sand, as follows: 
Feldspathic sand of Decize. 50 
Calcine with 18% tin 50 
Sea salt 3 
Carbonate of soda 3 
Or 
Flint 50 
Calcine with 18% tin 50 
Sea salt 8 
Carbonate of soda 3 
The quantity of sea salt, consequently of soda, is in- 
creased in the second formula to obtain the same degree of 
fusibility as the mixture containing the feldspathic sand. 
The presence of sea salt (sodium chloride) is necessary to 
obtain a perfectly white glaze even without any cobalt 
oxide. This property of sea salt seems to be due to the 
chlore it contains, although this point has not yet been 
clearly determined. 
The two formulas I have given produce absolutely 
perfect white glazes and are used in modern industry. 
They are far superior to the old glazes. They mature at 
cone 09.* 
The elements constituting these glazes are thoroughly 
mixed, then fritted. The fused mass is washed and ground 
to impalpable powder. This grinding is a very important 
operation upon which the successful decoration often depends. 
Many potters imagine that if a glaze is ground too fine it 
will crease after firing. This is absolutely wrong, as has 
been shown by the experiments which I have described in 
my pamphlet on "The Degree of Fineness which Glazes 
and Enamels should have." 
(TO BE CONTINUED) 
*Some Clays will be easily found which will give a well-fired body at 
that temperature. 
*> 1? 
SPANISH DAGGER (Page 253) 
Alice Willits Donaldson 
OUTLINE design carefully with Black and Violet, then 
fire. 
Second Fire — Paint in blossoms with a delicate Yel- 
low, shaded with Grey for Flesh and Violet. The leaves 
are Moss Green and Grey for Flesh. 
Third Fire — Wash background with Albert Yellow, 
Yellow Brown and Brown Green. Retouch flowers with 
same colors used in second fire. 
Pair Polychrome Tulip Vases, Delft Holland— XVII Century 
The property of the Metropolitan Museum, New York 
