220 RERAMIC STUDIO 
CLAY IN THE STUDIO. made without grinding and unless a color mill be available 
(Fourth Paper.) thev nad better not be attempted. A simple explanation, 
however, of their manufacture will not be out of place. 
Charles F. Bums The meta]lic oxides available for high temperature work 
HE taste of clay workers varies greatly with are not numerous. The list comprises iron and manganese 
regard to the color of their clay. The already mentioned, with nickel, cobalt and chromium, these 
maker of porcelain seeks a bluish white & ve colorants supply all the possible tints for clay. Cobalt 
and secures it by the use of a "reducing" produces blue, chromium green, and nickel brown or gray, 
fire in his kilns.* The manufacturer of They can be intermixed in any proportion giving a wide 
dishes seeks the same white, but, not being able to command range of colors which are, however, all of a subdued and 
the reducing fire adds a stain of cobalt blue to his mixture, somber character. There are certain colors which do not 
The terra-cotta man has to make wares to match the color of seem appropriate for the material under consideration. The 
brick or to please a fastidious architect and he resorts to the oxides which occur in the clay in its natural state are those to 
blending of natural clays until the required hue is obtained. which we turn with satisfaction. A piece of pottery made of 
Some artists like a white clay, some cream, others again a vivid green or rich blue clay would seem incongruous and it 
lean towards buff, brown or gray. To some the red of a well is perhaps a matter for congratulation that such do not exist 
burned brick is pleasing and to others there is nothing superior m nature. The introduction of small portions of bright color 
to the massive effect of Grecian black. How shall they all is > at the same time, sometimes admissible and therefore those 
be pleased? Obviously, if each can mix his own materials the oxides are not entirely ruled out. Oxides vary in strength, 
desired end will be brought within reach and therefore the Cobalt and nickel are powerful, chrome and manganese less 
following remarks: so and iron is the weakest. 
Clay contains one important and universal colorant, iron. I" compounding a stain for use in clay a nucleus of similar 
A clay without iron is rarer than a black swan, though the nature to the body itself should be provided. Such a mixture 
amount contained varies all the way from one-tenth of one as the following will answer well: 
per cent, to eighteen or twenty per cent. Clays as rich in Feldspar 55 
iron as this are almost iron ore and would probably prove too Flint ... 2s 
fusible for pottery purposes. They would be liable also to Kaolin 26 
burn to a violent red in the fire. Clays with one per cent, of 
iron can be used in white wares, the iron being only sufficient I0 ° 
to impart a cream color which is partly neutralized by the To this four parts of cobalt oxide will make a strong blue, 
flint added to the mixture. or three of nickel and one of cobalt a neutral gray. A corn- 
In the making of porcelain even more iron is permissible, bination of cobalt, chrome, manganese and iron will make a 
as the "reducing" fire already alluded to has the effect of black, but a black body is best made by adding cobalt to a 
turning the iron blue instead of yellow. The reducing fire, ricri red clav - The coloring matter in every case is well 
however, is not the ordinary method of burning so that it is blended with the mixture given above and baked hard in the 
safe to reckon that a clay will burn to a pale cream color as kiln. A small crucible may be built up out of some of the 
the nearest approach to white. Iron produces cream, buff, ordinary clay and then filled with the color mixture. When 
brown or red under normal conditions. Red brick and tile burned, this will be as hard as a stone. It must be removed 
owe their color to the iron in the clay and to the same cause, from the crucible, pounded and ground to a very fine powder 
but under somewhat different conditions, the buff colors of when it can be mixed with a suitable amount of body clay, 
terra cotta and floor tile are due. Darker browns are due to The proportion will depend upon the tint required, the strength 
the presence of manganese, an oxide which produces the of tne stain, etc. Usually about five parts of body to one of 
blackish glaze used on milk pans and stone jars. The white stain. These stains can also be used as under-glaze colors 
body mix given last month may easily be stained to a pleas- if desired and it is a great pleasure to make colors for this 
ing brown by the use of burnt umber, an earth which can be purpose. The under-glaze colors sold on the market are for 
procured cheaply through any druggist. The quantity used the most P art crude and harsh in tone. They are made for 
will depend upon the color needed. Three per cent, will printing as single colors and are not of the pleasing quality 
produce a fairly dark color. The umber should be added to which artists love. 
the dry clay before being made into slip. The color of the It: wil1 °e advisable for any one making a beginning in 
umber itself is due to the presence of both iron and manga- clav work ing to adopt one, or at most, two colored clays. It 
nese. A good buff is far more difficult to make, a fact which is a tiresome matter to clean up one clay in order to use 
illustrates the doctrine that Dame Nature can produce in her an other. Separate receptacles for scrap must be kept with, 
laboratory results which are denied to mortal man. Though oftentimes, separate water dishes and sponges. One clay of 
it is fully known that buff is due to iron, one may mix combi. a sat isfactory tint should be sufficient and if a change be de- 
nations of iron in endless variety and fail to secure the desired sired let ** De made completely, all the former color cleared 
color. The best way is to procure from a maker of stoneware U P and P ut awa y— in other words, be off with the old love 
or a dealer in common clays a clay which is known to burn to before getting on with the new. 
a buff or yellow. Then with white body and buff clay and For de corative work, a few glass fruit jars are ex- 
burnt umber almost any variety of color in drab, gray and cellen t— may be kept each with a portion of colored clay, 
brown can be secured. These can be used with a brush like ordinary colors and need 
Artificial stains are of course possible but they cannot be not interfere with the main clay in use. More will be said on 
this point when dealing with slip-painting or pdte-sur-pdte, but 
*The term " reducing " applied to fire refers to the chemical compo- this would anticipate the story, 
sition of the kiln gases and will be fully explained in a future paper. It is most desirable that different clays, if more than one 
