The Greeks appear at first as pupils and imitators of the Phœnicians, but they soon surpassed their teachers in forms as well as skill. They knew how to make their moulds so perfect, and were able to place their cores so near the mantles, that the castings were as thin as cardboard. The master founders of to-day have not reached that perfection.
HARD BRONZES OF THE ANCIENTS.
We have already seen that only very pure bronze is suitable for weapons and tools. It must be well "cooked," and all sulphur, lead, and tin must be completely removed by oxidation. The best results are obtained with from 8 to 12 per cent. of tin. A bronze having this composition is tenacious and has a hardness of at least 4.
But the ancients were able to make much harder wrought bronzes, as proved by our collections of weapons and tools.
Unfortunately we have no record of the devices employed; but as we are able to make just such products and with simple means, we may assume that the ancients employed essentially the same methods. In our experience the following conditions are essential for the manufacture of hard bronze:
1. A particular treatment.
2. A small amount of phosphorus.
It is well known that normal weapon bronze, unlike iron, is softened by rapid cooling, but is hardened by hammering and rendered more compact.[22]
By repeating this process, the bronze gains in hardness and strength, and sheet bronze becomes lamellar by hammering or rolling, and hence acquires a certain elasticity.[23] Besides, a slight admixture of iron or nickel seems advantageous, but a slight amount of phosphorus is of the highest importance. The latter point may be somewhat enlarged on.
Ordinary bronze always contains oxides of copper and tin, the quantity increasing with the number of times it is recast. This oxide makes it pasty, so that the different constituents do not separate, and the casting is homogeneous.[24] This admixture of oxide does no harm for castings in which strength is not demanded; but is of importance for weapon bronze; the strength of which is considerably diminished by the presence of the oxide.