There is still another method, less common in modern times, but employed by the ancients, for some of their smaller works. This is when a wax model is encased in clay or plaster of Paris and the molten metal then poured into it to melt the wax, and take the form of the work precisely as it left the hand of the sculptor. The original model is thus destroyed and the bronze takes its place. Some very large and important works have recently been cast in this method, but with the core. In bronze casting with a core, this contrivance must be made with great care. The mould, which is obliged to be formed of pieces fitted together, in order that the model may be taken out, is first well soaked in oil, then melted wax is applied to the inner side of the moulded parts in such thickness as may be required in the metal of the completed statue. But as a hollow metal statue would not be strong enough to support its own weight, a sort of skeleton of iron bars is made to take the general form of the figure, and this strong frame-work is firmly fixed within the mould. We have then the mould, with its wax lining, enclosing the iron skeleton, or _armature_, as it is called, with an opening left in the proper place to allow of pouring in the liquid plaster of Paris mixed with pounded brick, which fills the space about the armature. Therefore, if at this stage, the mould were taken to pieces again, the sculptor would behold his statue as one of apparently solid wax. Practically this is done in order that he may satisfy himself of the success of his work, and correct it where necessary. The model is then again placed in the mould preparatory to casting. _Galvano-plastique_, or the use of electricity, to deposit a thin layer of metal in a pure state upon a model, is an important invention or application of science to art. Having described the various materials and methods employed in sculptured art, we are ready to classify the different forms adopted and arrange them under the proper terms. Sculpture in relief is the first division. There are four varieties. _Bas-relief_, or _basso-relievo_, is the term used when the work projects from the plain surface, the forms being rounded as in nature. If the work is very little raised, the forms being not so projecting as in nature, it is called _flat-relief_, or _stiacciato_. If more raised, but not free from the ground in any place, it is _half-relief_ or _mezzo-relievo_. If the relief is still higher it becomes _full-relief_, or _alto-relievo_, in which parts of the human figure are entirely free from the ground of the slab. In _sunk-relief_, or _cavo-relievo_, the work is recessed within an outline, but still raised in flat relief, not projecting above the surface of the slab. Much of the renaissance and modern sculpture combines the first-named kinds of work on different planes in degrees of distance, with some under-cutting. The beauty and character of bas-relief depend much upon the representation of outline.