i6o 
hekamic studio 
CLAY IN THE STUDIO 
(Eleventh Paper.) 
diaries F. Binns 
HERE are several ways of placing 
glazed pottery in the kiln. "Plac- 
ing" is the pottery term for setting 
every piece in readiness. A kiln of 
painted ware is "stacked/' a kiln 
of biscuit or glaze is "placed." 
Wliether saggers are used or not 
will depend upon the type of kiln. 
Probably most of our studio workers 
will not use saggers. Iron supports 
in the kiln should not be used. If it is necessary to set more 
than one tier of pieces, earthenware supports must be made. 
This is the w^ay to make them: Take the ball clay which is 
used in the body of mixture and crush it into very small pieces. 
Have two sieves, one with 40 meshes to the linear inch and one 
with 20 meshes. Sift the crushed clay through the 20 sieve 
and again through the 40. Save all the small pieces of claj^ 
which have passed through the 20 sieve and lie upon the 40. 
Put this granulated clay in a biscuit jar and burn it in the kiln. 
The dust that goes through the fine sieve will do for body 
mixing so that nothing is lost. The granulated clay, when 
burned, is called " grog." It will not soften down in water and 
is very valuable as a constituent of clay for props, bats and 
saggers. A mix is now made of half ball clay and half 
grog worked up with water to a plastic mass and from this 
the props are made. These can easily be built by hand. They 
should be nearly solid but it is better if they are not quite so. A 
mass of the clay can be rolled around an iron rod or stout wire 
and when the wire is withdrawn the hole allows the escape of 
moisture and prevents the piece splitting. These props must 
be cut to exact heights if thej^ are to be used in sets. Bats can 
be made from the same clay. The clay is well kneaded or 
"wedged" as potters say, and rolled out to a uniform thickness. 
For small bats f of an inch is enough, large ones must be made 
thicker. Both props and bats should be well dried and burned 
in the kiln before they are used. 
Glazed pieces maybe placed on stilts or directly on the bats. 
If stilts are chosen pains must be taken to get an assortment of 
sizes so that every piece may be set securely on the three points. 
Sometimes a small vase is placed on the arms of a large stilt 
instead of on the points of a small one, this is almost sure to 
result in pieces being pulled out of the foot where the glaze has 
cemented the stilt to it. 
If there be a difficulty in procuring stilts to fit, small discs 
may be made of the prop cla}^ and set under the vase. These 
discs need not be burned first but they must be dry. If it be 
decided to set the ware directly on the bats thej^ must be pro- 
tected with an infusible wash. Equal parts of kaolin and 
ground flint, worked to a slip, may be painted on the bats with a 
large brush. This coating will peel up when burned and will 
help to absorb any glaze which may run down on the foot of the 
vase. A bat should always be set on the bottom of the kiln, 
for an expensive kiln may easily be ruined by an escape of glaze. 
The glaze should be so compounded as not to run but there is 
always the liability of accidents, besides, some beautiful effects 
are secured with glazes which are intended to run. 
In placing the kiln a space should be left for the cones. It 
is well to use three or four in each burn. For a temperature to 
reach cone I there should be used, say, one each of 06, 03, 01, 
I and 2, the first named are to give warning, they will bend 
perhaps one hour before the finish, cone 2 is the safeguard. 
It may happen that No. i goes down unexpectedly and No. 2 
stands there to show that no harm has been done. 
The bum should be arranged to finish in the evening and 
the kiln should be resolutely left unopened until the following 
morning. This may conduce to early rising but no matter. 
It is scarcely likety that the first few kilns will be faultless. 
Troubles are bound to arise. Not even the most experienced 
potter is free from them. A few of the most likely will be here 
enumerated and some suggestions made for their cure : 
I. — ^The glaze is crazed. One is not long in the ranks of 
clay-workers without becoming famiHar with this trouble but 
inasmuch as one is frecjuently asked "What do you mean Ijy 
'crazed'?" a word of explanation is given: The "craze " is a 
form of crackle. Small cracks develop all over the glaze but 
do not penetrate the boch'. Or long lines show themselves, 
often running completely around the piece. In wheel made 
pieces these lines frequently follow the spiral lines of the clay. 
Crazing does not always occur at once on drawing the kiln, 
sometimes it does not develop for months or even years. It is 
a troublesome fault and one of which potters have great dread 
There are several causes of crazing and, of course, several cures. 
The cause may, first of all, lie in the body, it may be short fired. 
If a harder fire can not be given it is best to try and remedy the 
glaze. Some changes have already been mentioned in connec- 
tion with the recipes given. Briefly, an increase in the flint 
will tend to cure crazing and is the simplest course to pursue. 
2. — The glaze is marked with "pinholes." This is mainly 
a body fault and is caused by small air bubbles beneath the 
surface of the clay. They are not seen either in the cla3^ or 
the biscuit but the glaze eats into them and shows them up; the 
remedy is to free the slip or clay from air bubbles. Pin holes 
are also caused by the body being too vitreous. Sometimes 
the fault is in the fire, the kiln being cooled too quickly will 
cause pin holes in the glaze. 
3. — The glaze is blistered. This is a much more compli- 
cated matter, fortunately, however, it does not often occur on 
artificially mixed bodies. Natural clays are subject to it and 
the shortest way out of the difficulty is to consult an expert. 
It is largely a matter of chemical constitution. 
4. — The glaze is scummed or frosted. Here again are 
several causes. A piece may have been placed close to an un- 
glazed waU or prop and the glaze has passed off in vapor, being 
absorbed by the biscuit surface. The effect of this is seen in a 
wrinkled, skin-like appearance. Or the glaze may be short 
fired, or over fired — the softer parts being volatilized. Scum 
may also be caused by a leak in the kibi waU. If a blast of air 
or smoke falls upon a glaze it will almost surely spoil it. The 
cause can usually be detected from the fact that exterior causes 
have an appearance different from that produced by composi- 
tion. If one side of a piece has the trouble and the other side 
is good the cause is surely local. If the whole glaze be uniform- 
ly damaged the cause is probably constitutional. 
5. — The glaze is shivered, even to the extent of bursting the 
pottery. This is the opposite of crazing and can be cured by 
working in the opposite direction. 
If any of tlaese troubles occur and they are famiUar to all 
clay-workers, it is not well to jump at a conclusion as to the 
cause. Body, glaze and fire should be^considered and even the 
water used in mixing. An experiment or two will help to 
locate the difficulty and the pleasure of overcoming it is great. 
The glazes given last month may be colored by any of the 
metallic oxides ordinarily in use. Copper oxide will give a 
transparent green, cobalt oxide a dark blue, manganese oxide 
a purple brown, iron oxide a yellow buff and nickel oxide, 
sparingly used, a grey. Mixtures of tliese will produce almost 
