242 
RERAMIC STUDIO 
GRAND FEU CERAMICS 
IX~SAGGERS, PLACING AND SETTING 
Taxile Doat 
HEN grand feu ceramics, gres or 
porcelains, are decorated and glazed, 
thej? must be set in the kiln for firing. 
The operation of setting consists in 
arranging the pieces in the lower room 
of the kiln, either free or enclosed in 
protective cases. When thej^ are of 
gres biscuit, not covered with glaze, 
thej^ can be fired on top of each other 
(Fig. 52) , provided however that open 
passages for the flame have been left around them on all sides. 
During the firingthe flames envelop and play upon these pieces, 
depositing unevenly on their surface a part of the alkalis, 
potash and soda, which the burning wood produces. These 
alkali salts do not injure the gres body in the least, on the con- 
trarjr, they give it the warm reddish brown tone so pleasant 
to the eye, and the semi-glaze which increases its permanence 
and densitj^ Moreover, in some cases, in order to accentuate 
this coloring and glazing, a few pounds of sea salt are thrown 
into the fire mouths during the firing. The free setting of gres 
biscuit pieces in the kiln has thus the double advantage of 
producing this surface quality and making it possible to use the 
whole capacity of the kiln without losing any room. 
saggers is a source of trouble and a continuous expense for 
ceramists. It must be prepared in great quantities and made 
into varied shapes, cylindrical or oval, according to the cera- 
mics to be protected. It constitutes the largest expense of all 
manufacture, large or small, because these utensils for firing 
must be made with claj's of first quality, easy to work and at 
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It is not so with porcelain. The salts from the burning 
wood, if deposited on the pieces, would give them an un- 
pleasant brownish tone. If the porcelain pieces are decorated 
and glazed, the effect of the salts is disastrous, causing a series 
of spots, consequently^ of flaws. It is therefore necessary to 
protect all porcelains, during every firing, whether in biscuit or 
glazed, as well as the glazed gres, and this protection is secured 
by hermetically enclosing them in fire clay boxes, which are 
called "saggers." The operation is called placing and is very 
important, as everj:^ thing which has to undergo the high 
temperatures of firing, must be arranged in the kiln with order 
and symmetry. The protective pieces are called, according 
to their shape, saggers, rings and hats. 
The saiggers are boxes with bottom (Fig. 40, p. 197, Jan. 
1904 and 54) . The rings, as the name implies, have no bottom 
(Figs. 41, 42 and 88) and they are used to raise the height of 
the saggers in accordance with the size of the pieces placed 
therein. The l^ats are round plaques or discs, which are 
placed on the bottom of the saggers to support the ware to be 
fired. They must be perfectly true to avoid their warping, 
which would involve that of the piece they support. These 
bats for bottom saggers (Fig. 53) must be distinguished from 
the similar pieces which are used for covers (Fig. 43) . 
The material which is necessary" for this careful placing in 
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the same time infusible.^They must be capable of standing 
repeated firings without softening or cracking, as their softening 
woLild cause deformation of the ware, while their cracking will 
be accompanied with the projection of grains of dirt, which may 
glide over the round surface of vases, but will irreparably 
adhere to the glaze of plane surfaces, such as plates, plaques, 
bowls, etc. 
The ideal material for this work would be an absolutely 
refractory clay of high plasticity, making possible repeated 
passages through the fire. But it is the geologist's work to 
find such a material for ceramists, and this ideal claj^ has not 
yet been found. 
The paste to be used for saggers cannot be exclusively 
made of plastic clay, the drying of which would be too slow and 
very difficult. It is necessar3^ to shorten the clay with an ad- 
mixture of grog made froiri the same paste already fired, pul- 
verised or in grains, according to circumstances. Pulverised 
for placing material proper, in grains for the making of blocks 
for the doors and especially for the covers of the fire mouths, 
also for all utensils in direct contact with the incandescent heat 
of the fire mouths. 
At Sevres, where all the placing material is given the great- 
est care, the composition of the paste varies in proportion of 
grog and clay, according to the use which is to be made of it. 
Here are the Sevres formulae: 
Outside material in contact with flame 
Clay of Provins 30 
Clay of Sezanne 20 
" Grog 50 
For inside bats 
Clay of Dreux 20 
CIslY of Retourneloup 15 
Crushed sand of Fontaine- 
bleau 32, 5 
Finely powdered grog 32,5 
