The oldest civilized races used bronze for a long space of time as
their chief useful metal, although some neighboring races understood
the metallurgy of iron. These facts, which are in glaring contradiction
to the present condition of things, require some explanation.
First it must be mentioned that _iron_ frequently contains injurious
contaminations, sulphur, phosphorus, etc., and that it must have been
very difficult for these primitive metallurgists to remove these
contaminations, and to introduce the proper quantity of carbon into
the iron. We must also consider that even a good, pure steel would be
a useless product unless it was worked by a skillful and experienced
smith. Finally, iron is much more rapidly destroyed by oxidation than
bronze. These negative considerations certainly favored the rule of
bronze for a long time.
The following facts must be fixed in mind regarding the manufacture of
bronze in olden times:
1. In many districts copper and tin ores are found near together (as
in Cornwall), so that under these circumstances bronze could have been
obtained by smelting both at once, and together.
2. In olden times only the upper horizon of copper deposits were worked
in all districts. In these, as we know, the ores are mostly oxides
(with native copper). Such ores are easily worked and yield largely.
3. In regard to the mixing of metals, the metallurgists everywhere must
have soon learned by experience that the metal remained soft and red
when too little tin was added, while too much tin made it light colored
and lustrous, but, at the same time, very brittle. Hence, we find that
among all peoples the alloys used for weapons contain from 6 to 16, or,
more closely, 8 to 12 per cent. of tin. These mixtures have been found
to do the best.
4. Bronzes, as we shall see below, by slight admixtures and certain
treatment, can be made so tough and hard that they will compare with
moderately hard steel.
So we see: The metal was useful, and there was an excess of rich and
easily worked ores. Under such conditions, of course, the age of bronze
would flourish a long time.
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.
2. Alloys from which ornaments, vessels, statues, and coin were
_cast_. Some of these contain lead, some zinc, and some are varieties
of our brass. I shall designate these as cast metals or ornamental
alloys. Those substances present in some quantity were evidently put
in _intentionally_, and I have classed them as admixtures, while the
unintentional ones in small quantities I have designated as impurities.
I.--WEAPON BRONZES.
_________________________________________________________________
| | |
Country. | Essential | Admixtures. |Impurities.
| constituents. | |
__________|___________________|______________________|___________
| | |
Egypt |Copper+ 6 to 14 tin| .. |Iron.
Assyria | " +10 to 14 " | .. | ..
Greece | " +10 to 12 " | .. |Fe. Ni. Co.
Italy | " +11 to 16 " |Lead and Tin. |Ni. Fe.
Gaul | " + 2 to 15 " | .. | ..
Britain | " + 7 to 14 " |1 to 3 per. ct. lead. |Iron
Alps | " + 8 to 12 " |Trace to 1 p. c. lead.|Fe. Ni.
Bohemia | " + 5 to 11 " | .. |Fe. S.
N. Germany| " + 8 to 16 " | .. |Nickel.
Denmark | " + 6 to 12 " |To 1 p. c. zinc. |Ni. Co.
Russia | " + 9 to 16 " |Lead |Ni.
__________|___________________|______________________|___________
II.--CAST METAL FOR ORNAMENTS.
_________________________________________________________________
| | |
Country. | Essential | Admixtures. |Impurities.
| constituents. | |
__________|___________________|______________________|___________
| | |
Egypt |Copper+ 4 to 11 tin|7 to 17 lead. |Traces
Assyria | " +10 to 14 " | .. |Pb. Fe. Ni.
Greece | " + 6 to 12 " |Lead. |Fe. Ni.
Italy | " + 1 to 7 " |Zinc, lead. |Fe. Ni.
Gaul | " + 5 to 15 " |Lead | ..
Britain | " + 5 to 15 " |2 p. c. lead. |Nickel.
Alps | " + 4 to 12 " |Zinc. |Pb. Fe. Ni.
Bohemia | " + 4 to 11 " |Lead. | ..
N. Germany| " + 6 to 17 " |Pb. rarely zn. |Ni.
Denmark | " + 5 to 12 " |1 p. c. zn. |Fe. Ni. Co.
Russia | " + 7 to 16 " |Pb. zn. |Ni.
__________|___________________|______________________|___________
The following general statements are based upon these tables:
We see that the peoples named forged their weapons and tools from very
different alloys; pure copper at one extreme, bronze with 20 per cent.
tin at the other. Experience had everywhere taught them that copper and
bronzes poor in tin are too soft, while bronzes with an excess of tin
could not be used for weapons and tools on account of being too brittle.
They had also learned that lead and zinc considerably lessened the
strength and tenacity of weapon bronze, while small quantities of iron,
nickel, and cobalt are, at least, not injurious. So all races, although
we can prove that they tried very different mixtures, finally adopted
very simple and tolerably constant alloys. The bronze weapons of all
countries frequently contain from 6 to 16 per cent. of tin, but usually
between 8 and 12, with slight contamination of iron and nickel. Few
nations have allowed lead to be used, fewer yet some zinc.
For casting, the oldest races used the same kind of bronze as for
weapons and tools. In many cases a few per cent. of lead were added
to make the casting easier. The Romans used zinc in addition to lead
in large quantity as a constituent of their alloys, and they made old
bronze, bronze-brass, and brass. Afterward many nations of middle
Europe used zinc alloys.
Small quantities of iron, nickel, and cobalt are found for well known
reasons in nearly all bronzes as harmless impurities.
Traces of _sulphur_ are also found in them. This injures the quality
of the alloy, and discloses the fact that such bronzes were not made
from pure oxide ores, but from those containing sulphur pyrites. At the
time when such bronzes were produced the mines had probably reached a
considerable depth.
Some of the weapon bronzes made by the ancients contain traces of
_phosphorus_, an element as important in hard bronze as carbon is in
steel.