THE CHOICE OF MATERIAL The modelling of a portrait head and the choice of size, whether life-size or over, is largely conditioned by choice of the material in which the head is to be cut or cast.
Wood, stone, metal and terra cotta provide a range of choice for the portrait sculptor, and each of these materials has its own technique. In Egypt stone was a favourite material, and the great simplicity of many an Egyptian portrait head may be due to the fact that the sculptor chose porphyry as his material for expression. Porphyry presents its own problems in the matter of carving. It is very hard, and necessitates the simplifying of surface treatment and the reduction of forms to their basic essen tials. In Greece and Rome, on the other hand, where marble was so largely used, the sculptor had more opportunity to display his skill in the handling of intricate surfaces with greater attention to detail.
The control of the material over the modelling and even over the general conception of the work undertaken may be readily understood if a porphyry head of the Egyptians, with its simple forms, is placed side by side with a Gothic group of the middle ages, carved from Caen stone or from some other soft stone material. No such flowering of detail and intricate design in sculpture would have been possible had the carvers of the middle ages and the Renaissance been confined to the use of a hard, unyielding stone.
The hard stone thus lends itself to conventionalization, urging the sculptor on to express form more or less symbolically, while the soft stone allows him to indulge his fancy for absolute realism and for intricate ornamentation.
and thickness, to the foot, and the heavier the bronze employed the greater the shrinkage.
Terra cotta, or dried clay, shrinks i in. to the foot, and does not shrink equally unless the model is so constructed that the shrinkage shall be equal. When the sculptor does not under stand the terra cotta material the parts shrink unequally and the original model is either distorted, cracked, or both. Distortion of terra cotta pieces that have come down to us from antiquity may often be attributed to this cause.
In dealing with the portrait head carved in wood the sculptor must appreciate that a solid block of wood checks or cracks. Many African and Chinese portrait carvings show serious cracks. This tendency, however, can be controlled if the wood is built up by dove-tailing or glueing together smaller blocks to produce the required volume, or by boring and excavating the interior of the large solid block.
The artist who feels for his material understands that it re quires a technique in keeping with its nature, and does not at tempt to force upon it some alien treatment. For example, the beauty of wood lies in the fact that it is wood, and the sculptor who uses it as a carving basis should treat it as wood and not give it a surface peculiar to the nature of marble. If, on the other hand, he desires for characterization the surface of wood as a base, he should not choose marble.