100 
RERAMIC STUDIO 
No. 22. Modern application of primitive process. Eookwood pottery vase, by Lenore 
Asbury. Painting with slip under ttie glaze. " 
I mean the scoriae constituting the refuse left by the reduc- 
tion of iron ores. There are two kinds of these scoriae: 
1 — Those coming from the modern blast furnaces. 
2 — Those coming from the reduction of iron ores in the 
Catalan furnace. 
The former cannot be used when they are completely 
vitrified in the shape of a translucent glass. One must select 
those which look like lava or metal, and which are also quite 
common. 
The other kind of scoriae, those from the Catalan furnace 
are very seldom vitrified and are consequently very good for 
our purpose. 
These scoriae are nothing but a silicate of iron, often 
calcareous or aluminous, according to the nature of the iron ore 
treated. 
This product is ground very fine, washed several times, 
and used as a glaze. It is applied very thin and if the firing 
is stopped at the time when the vitrification begins, one ob- 
tains a mat glaze, the tones of which, on the same piece, will 
vary according to the atmospheric modifications which occur 
in the kiln in the course of firing. 
The point of fusion of this glaze will vary according to 
the composition of the scoria, from 900° C. to 1200° C. 
It will then have to be regulated as follows: selecting a 
lot of scoriae weighing from 10 to 20 pounds (a very small 
quantity, but we should not forget that we are talking art 
ceramics, not industrial work), the mass will be ground as fine 
as vitrifiable porcelain colors (screen 250). Then it will be 
tested at the point of firing which the artist general uses. If 
it is found that the glaze is too hard, it will be softened with the 
flux which I have described above trying carefully the addi- 
tion of flux in small doses, 3%, 5%, d>%, 10%, etc., as it is 
important to obtain a mat color, not a brilliant one. 
A blacker tone may be obtained by the addition of 5 to 
15% manganese oxide, not forgetting that manganese has a 
tendency to slightly increase the fusibility. 
I think that by showing in a general way, as I have done, 
some processes of decoration to which we owe remarkable 
works of art, the tradition of which has since been lost, artists 
will realize that there is much to do in that line. 
Painted Decoration 
I wish now to say a few words about painted decoration 
such as it was understood by primitive potters, before the 
discovery of vitrifiable matters. 
Everybody knows that the three tones which were used by 
the marvelous artists of old Greece are: black, red and white. 
There is not the slightest doubt that Greek ceramics were 
the development of the much older art of the potters of the 
Aegean sea, who themselves had only perfected the still older 
processes from Eygpt and Asia. The palette used by the Aegean 
potters was more complex than that of the Greeks. Besides 
the black, red and white, it contained brown, orange and 
violet. All these colors, except black, were constituted of 
clays and ochres which wei-e applied on the raw body and 
which were burnt like ordinary colors. 
And it is extremely interesting to compare the colors used 
by the Aegean potters with those used in South America, 
No. 23 Primitive Process. Precolombian pottery from Nazca (Peru). Painting with clays or ocbrcs. 
From the Berthon collection, Paris. 
