278 
tlERAMIC STUDIO 
from Piccolpasso, also used for the smoking process broom 
wood, the green branches of which burn with much smoke. 
Martinez de Frugo's manuscript does not mention the fuel 
used by the Moors, but we find this information in the ac- 
counts of the Duke of Berry's tile manufacture in Poitiers, 
for which, as I said before, he had hired the services of a 
Moorish potter "Jehan de Valence, ovrer de carreaux", 
who ordered to be brought from Mintre "des fagots de genet" 
(sticks of broom wood). These accounts have been pub- 
lished by Mr. Magne. 
I have given much attention to this question of broom 
for fuel, as it was evidently considered by the old potters 
as absolutely necessary for the development of metallic 
deposits. I have tried a number of organic matters and 
have found that results were identical to those obtained 
with broom. Coal however has the great disadvantage of 
increasing the heat too much, a thing which it is important 
to avoid in this work. Ordinary green wood burns irregu- 
larly and the formation of gases is at times slow, at other 
times intense. Tar, petroleum, resins and oils are very 
good, because they give an abundant smoke without rais- 
ing the temperature in any noticeable way. Pieces of 
wood, paper or rags may be saturated with tar or oils and 
thrown into the fire mouth which is still hot enough to 
develop a strong formation of hydrocarbons, without gener- 
ating flames. 
However the best process consists in the use of ordinary 
illuminating gas, but the reduction then is so intense that 
the operation must be watched with great care. The 
muffle I use in this case has its sides pierced with four holes 
(two on the left side and two on the right), having twenty 
millimeters in diameter and placed three centimeters above 
the muffle bottom. With a large muffle kiln, the number 
of holes should be increased to six, eight or ten. These 
holes are closed with clay during the first part of the firing 
to cone 09. Close to the outside walls of the kiln runs a gas 
pipe, supplied with as many valves as there are holes in the 
kiln walls. When the time has come to reduce, small iron 
pipes, attached to the valves with rubber tubes, are intro- 
duced into the holes so that they will protrude inside the 
muffle to a distance of about two centimeters from the in- 
side wall. After the tubes have been introduced, the 
holes must again be carefully closed with clay, to avoid a 
gas explosion which might be produced by the mixture of 
air and gas, or the combustion of the gas. Generally there 
will be some flame produced at first, because of the air in 
the muffle, but as soon as the oxygen is absorbed, the com- 
bustion stops. 
Six cubic meters of gas per hour should be used for a 
muffle having one cubic meter capacity. 
The time of reduction is of great importance, since the 
color of the metallic deposits depends upon it entirely. We 
have seen that silver mixtures will, according to the time of 
reduction, pass from brass yellow to brown, then to black. 
Passeri says that the third firing lasted six hours, not more, 
but this evidently included the firing proper, which takes 
about three hours, so that the reduction must have lasted 
about the same time. 
I have obtained metallic deposits as brilliant and clear 
as the old ones, with the use of coal, tar, petroleum, oils and 
resins, and I have brought down to two hours the time of 
reduction, but this operation was conducted with great 
regularity and there was no stop in the formation of hydro- 
carbons. With vegetable fuel, three hours at least are 
necessary. I have kept the reduction during five, eight and 
ten hours ; the metallic deposits have become very dark, but 
not black, as happens with illuminating gas, when the re- 
duction lasts only 35 to 40 minutes. 
It is very difficult to study the different stages through 
which metallic deposits pass, when an ordinary fuel is used, 
on account of the length of time, but with gas the reduction 
is over in ten minutes and must not exceed thirty minutes, 
as above this limit the metallic effects and iridescence dis- 
appear. 
There is still another way to obtain the deposits. It is 
the introduction into the muffle, at the time of reduction, 
of some sugar compound. This is done through an open- 
ing either in the walls or the vault. The temperature of 
the muffle is high enough to allow an abundant formation 
of gases, without burning the sugar too rapidly. The 
operation must last at least two hours. This method is very 
simple, but the results are uncertain. 
To sum up, the best and most practical reduction is 
obtained with illuminating gas. 
APPEARANCE OP GLAZES AFTER REDUCTION. 
The iridescent glaze formulas 1 a to 6a come out of the 
muffle after reduction with brilliant iridescence and do not 
need any polishing. It is not so with deposits formed over 
the glaze (formulas 1 to 6). These do not exactly need to 
be polished, but they are covered with the ochre mixture 
which has helped their formation and which is more or less 
adherent according to the more or less intense firing. This 
covering is easily removed with a wet cloth, and, if necessary, 
some finely ground sand. The metallic iridescence then ap- 
pears in all its brilliance. 
This ochre residue coming from the scrubbing of the 
ware, is rich in copper, silver or bismuth oxides, and was, as 
we have seen, called by the Moors "scoria" and was used 
to be added to the next metallic mixture. 
(TO BE CONTINUED) 
IK'S? 
c 
TEAPOT— INA C. BRITTON 
Incised and glazed in soft green. 
