CHAPTER XVI: DECORATION

The necessity for some kind of decoration upon the clay will always be a point of difference amongst artists. Some prefer the simple form with a glaze treatment only, others consider that the surface should be broken up by design. The question will not be debated here. The aim of this hand-book is instruction and the individuality of the worker is to be encouraged. Directions for executing the different treatments do not imply that these elaborations are advocated. That must be left to the inspiration of the worker.

Decorations may be applied upon the soft clay by incising, inlaying and embossing; upon the dry clay or upon the burned pottery in color under the glaze or with no glaze at all; in the glaze by the use of colors or colored glazes; or over the glaze with colors and enamels. Each of these methods possesses special features. Each has its own possibilities and limitations and these should be mastered by the craftsman.

As in the production of form a well-planned design should be prepared. The first sketch should be made on paper or on a slab of clay but the fitting and final arrangement are best made on the piece itself.

Incising consists in the excavation of a shallow trench or trough on the surface of the clay. The vase or jar having been finished should be kept in a damp place so that the clay does not dry out completely. The design may be made in India ink with a brush. A steel tool with a narrow chisel end is used for cutting and care must be taken that the clay is in such a condition of moisture as will admit of a clean trench being dug without any rough or broken edges. The bottom of the trench need not be very smooth but the edges should be sharp and the lines well defined. At the same time a mechanical hardness of finish is to be avoided. The plastic nature of the clay should be kept in mind and every surface, though decided in character, should be soft and expressive. This result can be secured by working over the cutting with a moist camel-hair brush. The work must not be mopped so as to leave a woolly effect, but a little sympathetic penciling will remove the hard lines of the tool.

There are two possible developments of incised work. The details of the design may be excavated or the background may be cut out leaving the drawing in relief.

In modeling embossments the piece should be a little softer than for incising. It is important that in any clay work attached to a clay body the same amount of moisture should be present in both parts. This is not entirely possible in modeling upon forms which have already been shaped, for if the form be as soft as modeling clay it will not bear to be handled, while if the clay were as hard as the form it could not be worked. A compromise is therefore necessary. The vase must be kept as soft as possible consistent with holding its shape and the clay must be as stiff as the working will allow.

As little water as possible should be used and the modeling should not be brought to its full height at once. If the clay be laid on little by little there is much less chance of cracking. Low relief is sometimes produced by painting in slip but here even more care is necessary. The slip should be laid on with a brush in thin coats, each coat being allowed to stiffen before another is applied and the whole work being kept moist.

An atomizer with clean water is useful in this regard. The work, being kept on a whirler or turntable, is sprayed now and then with water and thus prevented from becoming too hard.

When the slip work has been raised to the desired height the surface is tooled over so as to remove the brush marks. This is the method which has been brought to such perfection by the French artists and by them named _pâte-sur-pâte_.

Modeled work is generally carried out in the same clay as that of which the form is made and depends upon high relief for its effect. Slip painting is usually done in a different color and if a light-colored slip be used upon a dark clay, the latter is partially seen through the coating in the thinnest places. This fact is made use of to accentuate the shadow effects.

In using one clay over another great care must be taken to insure that the fire shrinkage is the same. The white body already given, or indeed, any light colored clay, may be tinted by the addition of under-glaze colors. The dry color, if sifted very fine, may be added to the plastic clay by thorough kneading and wedging but it is better to work up the clay into a slip and to stir in the color. The tinted slip is then lawned two or three times and dried out on plaster or used in the slip state as the case may be.

A trial should be made before any important work is undertaken, both to see that the color is right and to discover any discrepancy in shrinkage. If a clay shrinks too much, a little ground flint may be added. If it shrinks too little, a little ball clay will correct it. The tint produced by the color is apt to darken in the kiln but the general hue will be similar to that of the color used.

For some classes of work a native red clay gives admirable results. It may be lightened by the use of kaolin and flint and darkened by adding burnt umber. These colors are more satisfactory than greens and blues in clay because the brown and red tones are natural, the others are artificial.

If a good buff-burning clay be available, it forms the best possible foundation for color work. Burnt umber will darken it and red clay may be mixed with it, always having regard to the matter of shrinkage already mentioned.

Very pleasing effects may be produced by inlaying one clay with another. The pattern or design is first cut out as described under incising and then the second clay is pressed, morsel by morsel, into the excavation. The surface is cleaned off level with the body of the piece and the whole may be either polished or glazed.

A plastic clay can be polished when leather hard and the finish will remain after firing. Any tool of steel, boxwood or ivory will do the work but a good supply of patience is needed so that the whole surface may be uniformly treated.

For color decoration upon the pottery, ordinary underglaze colors are used, either upon the unburned clay or upon the burned ware commonly called biscuit. For use upon the clay, the colors should be mixed in water, using a little molasses, sugar, glycerine or gum arabic to make the color flow easily from the brush. Before burning, a little glaze should be sprayed over the work with an atomizer. Any ordinary fusible glaze will do. It is diluted with a good deal of water as only the very thinnest coat is necessary. The spray should not be held long in one place or the water will flow and smear the color. If the piece be turned slowly around the clay will absorb the water as it is applied. If this spraying be not done the colors will be apt to rub off after burning. Under-glaze colors are not fusible and hence they come from the fire as dry powders.

The work on the biscuit is much the same except that turpentine and fat oil constitute a better working medium. When dry the spray should be applied as before.