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: