Pottery decoration under the glaze

by M. Louise McLaughlin

A palette or a slab of glass may be used for mixing the colors and clay. The latter is the best, as it can be procured of large size, and as in this kind of work a considerable quantity of paint is necessary, there should be ample room to mix the colors. A slab of French plate glass, at least twenty by twenty-four inches, may be procured. This can be imbedded in plaster of paris, which will make it stronger, as well as furnish a white surface upon which the colors will show to better advantage.

The powdered colors as procured are not perfectly pulverized, and must be well rubbed down with a muller and palette knife. It is even more necessary in this than in other kinds of painting upon pottery that the color should be well ground. If not rubbed down sufficiently before being mixed with the clay, particles of color which are scarcely apparent before firing, will show when the work is glazed, forming specks in what should be, a perfectly uniform tint. If the color is mixed with the clay before it has been perfectly dissolved, it will not afterward be possible by any rubbing down to remove the specks from the mixture.

The colors, after being thoroughly ground, can be mixed with clay in such proportions as may be desired. The white clay takes the place of white, and is used to lighten every tint, as well as to form a body for the colors. It is a good plan, where experience has rendered it possible to do it with judgment and certainty of result, to mix the various tints in water with clay, in quantities, and then allow them to dry. When dry, they can be pulverized and the colored powder can be put away in bottles for future use. This saves time when painting, and also ensures a like result from the use of a mixture which has already been tested and found to be satisfactory. It is only, however, after considerable experience in mixing colors, and verifying their results, that this can be safely done.

As in other kinds of underglaze painting, it may be given as a general rule, that the colors are intensified in firing, in this, however, much more than in other methods. All the stronger colors are intensified to a degree difficult to realize before experience has taught the artist what to expect. They all become several shades darker, and, in the case of blues, blacks and greens, it is more difficult to obtain delicacy, than depth of tint.

In the use of scarlet, crimson and yellow, a considerable amount of the color in proportion to the clay must be used for the darker portions to give sufficient depth. Only enough clay must be taken to give body to the paint, and the mixture should then be applied very thickly. The painter must also bear in mind the fact that the stronger color will overpower the weaker in mixtures, even when the latter is in such degree as to give the color to the mixture before firing. After firing, the stronger color will appear in excess. In making such mixtures, therefore, the stronger color should be used very sparingly, if it is desired that the other should predominate in the tint when fired. Otherwise, the colors may be found after firing to be entirely different from what was intended.

METHOD OF PAINTING.

Let us suppose that the artist wishes to paint a vase. A certain tint being selected for the ground, the color, or colors, which are to produce it are mixed in their relative proportions, according to the hints given above. A sufficient quantity should be prepared to paint the whole ground, especially if a mixed tint, which it would be difficult to reproduce in its exact proportions. It will require some little experience to enable the artist to judge how much will be needed, and, perhaps, it will be somewhat difficult for any one accustomed to painting in other methods, to realize the quantity of paint used in this. It is better to have too much mixed than too little, as it can be kept and used another time.

The color, or colors, for the ground having been rubbed down until perfectly smooth, as directed before, may be mixed with more or less clay, according to the shade of color desired. The first tint may be made to represent the darkest shade in the ground, and a comparatively small amount of clay should be used. After the color has been mixed with the clay, it can be placed on one side of the palette. By taking portions from it and adding more clay, other shades of the same color may be made. First, a light tint may be prepared for the first coat upon the vase.

Before commencing to lay on the ground, it is well to wash the surface of the vase with a thin solution of glaze (such as is used for finishing the ware), or with borax water. This is to ensure the adhesion of the clay, of which the painting is to consist, to the clay of which the vase is made. Previous to this, the vase, if not already in good condition, should be washed over with a brush, or with a sponge dipped in water, or sprinkled until it has absorbed water enough to keep the clay, which is to be applied to its surface, from drying too quickly.

A broad, flat camel’s-hair brush may then be charged with the light tint, and the surface of the vase covered with it as evenly as possible, and so thickly as to completely obscure the body. This done, another tint, darker than the first, in a degree sufficient to permit their being distinguished from each other, may be mixed. This will form the middle tint of the ground, and is to be laid on over the first. The reason for applying two coats is, that, although it might be possible to paint one with the degree of thickness necessary to prevent the shrinkage of the applied clay in the firing, from revealing the body of the vase, still the beginner is very likely to be deceived as to the thickness of the impasto, judging by the eye alone. Potters dip pieces of ware in colored slips, and the thickness of the covering thus formed is all sufficient. In the case of painting, however, it is impossible to lay the clay on as evenly, and there will be, in all probability, some places too thinly covered to stand the fire, but which would not be revealed before. It is better, therefore, to apply two coats, so that one may cover up the deficiencies of the other. The reason for having these two coats of different tints is, that it is then possible to be assured that the surface is covered completely, it being easy to distinguish the first tint laid from the body of the vase, and in the second painting, to observe that it entirely covers the first.