Zinc ores frequently occur on copper beds, and yet zinc is rarely found in quantity worth mentioning in the bronzes of the ancients. There are two reasons for this:
1. Near the surface of the earth zinc occurs as calamine (silicate of zinc), which is a gray, unattractive, earthy looking mineral, not heavy enough to be taken for a metallic ore, and would naturally be thrown away and not put in the furnace.
2. If some zinc ore did get into the furnace, part of it would be volatilized and part oxidized by subsequent smelting.
In later times, however, we find zinc ores used a good deal. We can distinguish three types of zinc alloys:
1. Copper with 10 to 20 per cent. zinc produces a red metal, red brass, which is similar to bronze that is poor in tin.
2. Copper with 20 or 30 (and even 40) per cent. of zinc, gives a yellow metal (yellow or ordinary brass), which has more of a golden color than bronze with much tin, but quite brittle.
3. Statuary metal, which is made of copper with quite a good deal of zinc and little tin (often lead) can be called brass containing tin.
All three types may be used for casting (ornaments, statues, and coin), but are not useful for tools or weapons, because they have not sufficient strength.
After discussing the natural association of ores, and the most important alloys of copper, we will turn to the analyses of antique alloys. I have found it necessary to divide them into two groups:
1. Alloys from which the weapons and tools were forged. These are pure and genuine bronzes. I shall designate them as malleable metals or weapon bronzes.