After a building was finished the sculpturing of its walls had to be executed. For this, a long training of sculptors was needful, and the art schools filled an important part in education. The simplest subjects of outlines in limestone were a first step, the sign _neb_ requiring a straight and a curved line only. After the geometric forms came studies of heads and of hands. In fig. 88 we see how, after a fair control of the graver had been attained, there was still much to be learned in detail and harmony before the artist could be trusted to decorate a temple. Statuary also needed a long training. The work was first marked out in profile of the front and sides, and then cut along these outlines, as in the rock-crystal figure (fig. 89), where the outlines at right angles have been cut, but the corners are yet unrounded. In the block for the head of a lion (fig. 90) the various planes have been already cut for the face, before attempting any rounding. The limestone head (fig. 91) shows a further stage, where the general rounding is done, but the details of the lips, ears, eyes, and eyebrows are yet left in the block. All of these stages needed incessant practice, and years must have been spent in training in the schools before final work was undertaken. [Illustration: STONE VASES 87. A-H. Prehistoric J. VIth dynasty K. XIIth dynasty L, M. XVIIIth dynasty] Turning now to stone-work on a smaller scale, the hardest materials were wrought for vases in the prehistoric age. In the first civilisation, basalt, syenite, and porphyry were in use as well as the softer stones, alabaster and limestone. The later civilisation brought in slate, coloured limestone, serpentine, and lastly diorite, which continued to be the favourite stone into the pyramid age. The main differences of form are shown in fig. 87. The earlier type of vase is the standing form F, with a foot, and no piercing for suspension. The later prehistoric age brought in the suspended stone as well as pottery vases. The main types were A, B, D, E, G, H, and lastly C, cut out of coloured marbles, of syenite, and of basalt. All of these vases were cut entirely by hand without any turning, or even any circular grinding, on the outside. The polish lines cross diagonally on the curved sides, and the slight irregularities of form, though imperceptible to the eye, can be felt by rotation in the fingers. The greatest triumph of this stone-work is the vase from Hierakonpolis in black and white syenite, of the type A, E, two feet across and sixteen inches high, which is highly polished, and hollowed out so thin that it can be lifted by one finger, though if solid it would weigh four hundred pounds. The interior of these vases was ground out with stone grinders fed with emery, and in softer stones cut out by crescent-shaped flint drills. [Illustration: METHODS OF SCULPTURE 88. Trial piece of learner 89. Rough drafting 90. Lion’s head drafted 91. Head nearly finished]