RERAMIC STUDIO 
131 
CLAY IN THE STUDIO 
(Tenth Paper.) 
Charles F. Binns 
HE time has now arrived for the 
consideration of the problems of 
glazing and it is a matter for serious 
consideration how to put the neces- 
sary^ information before those who, 
presumably, have had no scientific 
training. All things considered 
it will perhaps be best to revert to 
the empirical way of doing thijigs. 
This is not the best teaching we 
admit Init it affords tlie shortest path to results and if more is 
wanted some systematic instruction must be sought. 
The ordinarj^ glazes available for the studio will be sucli 
as can be mixed from materials which can be readily procrn-ed 
and which need no preparation. A glaze is a com]3oiuid of 
fusible and infusible materials so balanced that at the right 
temperature the mass will melt and flow. The term "fusilDle" 
is, of course, relative. None of these substances is actuallj' in- 
fusible but is so at ordinary temperature. Others again are 
very hard to melt w^hen alone but fuse readily wheir certain 
other ingredients are present. For glazes so compounded the 
. all-important substance is lead. White lead is generally used 
because it can be readily worked up in water but red lead 
would do the work. \ATiite lead supplies a base with which 
the other ingredients of the glaze freely combine and hence it 
forms an indispensable constituent of simple glazes. 
For a lead glaze to fuse at cone I, on the body already 
given there wotdd be taken 
73 ]inrts ))v weight 
8 
19 — TOO 
glaze, yellowish in color and some- 
what inclined to craze on certain bodies. In order to harden 
or stiffen the glaze some of the lead may be left out and wliiting 
or paris white substituted 
White lead 62 
Paris White li 
Kaolin (S 
Flint 19—100 
This glaze will also he whiter than the iirst and less lial^le to 
craze. 
A still better glaze can be made bj^ the introduction of zinc 
oxide but this must be added sparingly as it will impair the 
brilliancy of the glaze if used in excess. Zinc makes the glaze 
whiter and somewhat stiff er 
White lead 54 
Paris white 13 
Zinc oxide 6 
Kaolin 8 
Flint 19 — 100 
Yet another change may be given and as it will involve an 
entire change of proportions an explanation will be advisable. 
It is well known that the use of the materials Avhich nature has 
provided is advantageous to the potter. Rocks and minerals 
are found which are already in a fused and glass-like condition 
and such substances are of the greatest use to the glaze maimer. 
Many of these natural products are colored, they contain 
oxides of ii'on and manganese which are undesirable in water- 
white glazes, but feldspar is an exception. This has alreadj' 
been mentioned as an important constituent of the bodv mix- 
ture and it is also available for glazes. But the addition of 
feldspar necessitates a re-arrangement of the glaze by reason 
White lead 
Kaolin 
Flint 
This will give a ver\' soft 
of the fact that it is a complex stdjstance. It contains potasli, 
alumina and silica and would cause an excess of these were not 
the alumina and silica derived from clay and flint proportion- 
ately low^ered. 
The mixture will now read 
White lead 50 
Paris white 8 
Zinc oxide 6 
Feldspar 20 
Flint 16 -TOO 
enough alumina being present in the feldspar the Icaoliii has 
lieen entirely omitted while the potash which the feldspar con- 
tains has displaced some of the lead and paris white. 
One of these four glazes \\n\\ probably answer the pm'pose 
of any one who is working at a low temperature but if it shoidd 
1)e desired to make a change the lines upon which this should lie 
done will be indicated. The important ingredients for stift'en- 
ing are clay and flint, either one alone will not answer the yjur- 
pose, thej7 must be increased together and proportionately, tlie 
increase of the flint being double that of the clay. Thus in 
glaze No. 3 a harder mmture will be secured bj^ increasing the 
clay to 9 and the flint to 2 t parts and harder yet by making the 
clay 10 and the flint zt,. This action may also be taken if a 
glaze is found to craze. The silica in clay and flint checks the 
crazing and the alumina prevents the silica having a bad effect 
upon the brilliancy of the glaze. At the same time these addi- 
tions must inevitably make the glaze less fusible so that a 
stronger fire is necessary to secure maturitj'^. 
The materials may be secured from any dealer in chemicals 
and are usually found to be sufficiently pure. The kaolin, 
flint and feldspar which have been used in mixing the bod.y are 
quite suitable. 
The weighing lieing completed the whole itiixture is put 
into a mortar and thorough^ ground. When all the lumps are 
broken dowm water should be added to produce a very thick 
batter, thin enough to flow down the sides of the mortar but 
no more. This must be again thoroughly ground to secure a 
perfect incorporation with the water. The worker on a large 
scale simply puts the whole batch into a mill and thus accom- 
plishes what the less favored must do by hand. Labor mixst 
not be grudged at this point and let it be a consolation to know 
that the finest effects of the Japaiiese and Chinese potters are 
produced with hand-ground mixtures. 
A fine sieve should now be brouglit into requisition and 
the glaze mixture thinned with more water poured on to it. 
Small clay lumps may be rubbed through but any grit must be 
rejected. 
There are several ways of glazing pottery but only two in 
general practice. These are dipping and spraying. The latter 
need not be explained in detail as it involves the use of com- 
pressed air, the former is practised on two lines, porous ware 
dipped in thin glaze and non-porous in thick glaze. The 
former is the general factory method and is the more rapid but 
unless there be a large tubful of glaze it is iiTipracticable. The 
l)orosity of the body renders a verj^- rapid action necessary or 
too large a bulk of glaze wiU be taken up. Such rapid action is 
the outcome of long practice and is not to be attained without. 
The non-porous ware then offers virtually the only pos- 
sible course in the studio. To secure this condition every 
piece of ware to be glazed must be soaked in clean water luitil 
it has taken up all it wiU hold. The glaze must be of the thick- 
ness of good cream. So thick that w^hen the finger is dipped 
into it a good white coating remains on withdrawal. It must 
be such a coating that cannot be shaken off. If the irregu- 
larities of the skin show through the glaze on shaking the finger 
the mixture is too thin. If left to stand for half an hour a 
