Pottery decoration under the glaze

by M. Louise McLaughlin

When the piece decorated is thoroughly dry, it should be fired at a temperature sufficient to make the body durable, and at the same time to perfectly fix the colors of the painting, so that there may be no danger that the glaze will cause them to run in the final firing. This latter defect may also result from an excess of glaze, and where it exists only in a very slight degree, produces a melting softness which is very pleasing. This effect is, however, so likely to be exaggerated to the ruin of the work that it is best not to run any risk of the kind in firing, and to depend upon the painting alone for the harmonious blending of the tints.

The temperature at which the work is to be fired, must, of course, depend upon the qualities of the clay of which the piece of ware is made. As has been said before, this clay should be one that does not require an excessive degree of heat in firing. The exact degree can be estimated by the potter who understands the requirements of the clay which has been used in the manufacture of the particular piece of ware in question. It may be said that the temperature at which Rockingham ware is fired is suitable for this work, and that a glaze such as that used upon that kind of ware can be used with good results. It is possible to have a glaze so adapted to the body of the ware as to prevent it from crazing, and yet preserve the brilliancy of the colors.

CHAPTER V.
MODELING IN RELIEF.

Under this head may be comprised the decorative modeling of figures and other designs upon pottery, in various degrees of relief. First, we have figures in relief forming decorations upon vases. These, as well as other designs in high relief, belong properly to the domain of sculpture, and the methods of producing them do not vary essentially from those in use in that art. The final process in this case is the firing, instead of the casting in plaster and cutting in marble.

Of the methods of producing floral designs in relief, a few suggestions may be of use. These, as well as the painting described in the previous chapter, must be executed when the body of clay, to which they are applied, is very wet, and the applied clay must in this case be, as nearly as possible, in the same condition. If the clay is not in the proper condition, the work will crack in drying.

The vase which is to be decorated being in the right state, a lump of clay, having the plasticity necessary for modeling, is procured. This may be of C. C., a deeper cream color, or red, according to the color desired. White granite is not plastic enough, and is, besides, liable to crack in drying. But of all white clays, parian forms the most beautiful substance for this kind of modeling. Leaves and petals of flowers can be shaped from pieces of clay, which have been flattened to the required thickness, either by pressing upon a slab of plaster of paris, by means of a weight, such as potters use; or, if the work is not on a large scale, the clay can be shaped in the palm of the hand. The forms can then be cut with a sharp modeling tool. If there is more moisture in these pieces of clay than in that which forms the body of the vase, they should be allowed to remain a short time upon a dry plaster slab. The plaster will quickly absorb the moisture in the clay. When ready, the pieces can be placed in position on the vase, the places where they are to be applied having been previously washed with clay and water (technically called “slip”), or with glaze water, to make them adhere. Stems are made by rolling pieces of clay between the palms of the hands, or upon a flat surface of wet plaster or wood. They are afterwards allowed to dry, and when in proper condition, applied in the same manner as the flowers and leaves. Delicate touches may be put in with a brush dipped in clay, of a proper consistency for painting. The forms of the design can be shaped and finished after they have been applied to the vase by the use of modeling tools, and, finally, with a camel’s-hair brush. The design may also be brushed over with a sponge, moistened with water, which will also be found very useful in restoring the smooth surface of the ground, if it has been injured in the process of modeling.

After the modeling has been completed, the work should be gone over with a modeling tool, and in places where a mass of clay has been attached to the surface, the edges should be under-cut. This will prevent cracking. If this precaution is not taken, a crack thus produced may extend into the body of the vase and render it unfit for firing. Where a large mass of clay occurs in the modeled design, it is better to hollow out the projection from the inside of the vase, to prevent the cracking or warping of the whole in firing, caused by the unequal thickness.

Cracks, which may appear in drying, should be filled, or, if possible, be pressed out with a modeling tool, before the piece is fired. If the crack is so deep that it is necessary to fill it, the place should be cut open with a modeling tool, moistened with water, and filled with clay, as nearly as possible in the same condition as that upon the vase.

Flowers can be modeled in parian clay upon a creamy-tinted ground with good effect. Various colors of deeper tinted natural clays, or clay which has been artificially colored in the body, can be used as the ground of such decorations. Light grounds are sometimes colored after the first firing, in the biscuit; or a ground can be painted in the method described in the previous chapter, while the vase is soft, and the modeled decoration can then be applied instead of the painting.