Considerable metallurgic knowledge and skill were shown in the composition of the pigments, and the preparation and application of the glaze wherewith they are covered. The red used was a sub-oxide of copper; the yellow was sometimes oxide of iron, sometimes antimoniate of lead--the Naples yellow of modern artists; the blue was either cobalt or oxide of copper; the white was oxide of tin. Oxide of load was added in some cases, not as a coloring matter, but as a flux, to facilitate the fusion of the glaze. In other cases the pigment used was covered with a vitreous coat of an alkaline silicate of alumina.
The pigments were not applied to an entirely flat surface. Prior to the reception of the coloring matter and the glaze, each brick was modelled by the hand, the figures being carefully traced out, and a slight elevation given to the more important objects. A very low bas-relief was thus produced, to which the colors were subsequently applied, and the brick was then baked in the furnace.
It is conjectured that the bricks were not modelled singly and separately. A large mass of clay was (it is thought) taken, sufficient to contain a whole subject, or at any rate a considerable portion of a subject. On this the modeller made out his design in low relief. The mass of clay was then cut up into bricks, and each brick was taken and painted separately with the proper colors, after which they were all placed in the furnace and baked. When baked, they were restored to their original places in the design, a thin layer of the finest mortar serving to keep them in place.
From the mimetic art of the Babylonians, and the branches of knowledge connected with it, we may now pass to the purely mechanical arts--as the art by which hard stones were cut, and those of agriculture, metallurgy, pottery, weaving, carpet-making, embroidery, and the like.
The stones shaped, bored, and engraved by Babylonian artisans were not merely the softer and more easily worked kinds, as alabaster, serpentine, and lapis-lazuli, but also the harder sorts-cornelian, agate, quartz, jasper, sienite, loadstone, and green felspar or amazon-stone. These can certainly not have been cut without emery, and scarcely without such devices as rapidly revolving points, or discs, of the kind used by modern lapidaries. Though the devices are in general rude, the work is sometimes exceedingly delicate, and implies a complete mastery over tools and materials, as well as a good deal of artistic power. As far as the mechanical part of the art goes, the Babylonians may challenge comparison with the most advanced of the nations of antiquity; they decidedly excel the Egyptians, and fall little, if at all, short of the Greeks and Romans.