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Hiram Bingham, the American explorer who found the
ruins of Machu Picchu in 1911, wrote:
Inca bronze has been found to be remarkably pure, aside from very small
quantities of sulphur. The proportion of copper in Inca bronze varies
from 86% in some articles to 97% in others. Some archaeologists have
taken the position that since the greatest quantity of tin is usually
found in those bronzes that would seen to require it least, the presence
of tin in Inca bronzes should be regarded as accidental. This hypotheses
has been carefully considered by the experts of the largest copper
companies now known that during World War II enormous quantities of tin
were recovered from Bolivian mines where our manufactures were delighted
to secure supplies to take the place of those that came from the Straits
Settlements before the Japanese occupation. It is also well known that
enormous deposits of copper are found in Peru and in Chile but not in
combination with tin.
My friend Professor Charles H. Matthewson of Yale University, was the
first modern metallurgist to make an exhaustive study of Inca bronzes.
He discovered that the percentage of tin contained in Inca bronzes was
not governed by the uses for which they requirements of the ancient
methods of manufacture. Everything that we know about Inca metallurgy is
based on Professor Matthewson’s report.
The Incas learned the interesting fact that bronze containing a high
percentage of tin yields the best impression in casting because during
the process of solidifying it expands more than bronze having a low tin
content. Hence the more delicate or ornamental pieces contain the
highest percentage of tin. Artistic details were thus more strikingly
brought out in the finished product. Of course, had the Incas possessed
steel graving tools the case would have been different. However, the
Inca metallurgists learned that the operation of casting small delicate
objects is facilitated when there is about ten percent of tin in the
mixture. Such alloys retain their initial heat longer and so remain
longer in a fluid condition. Since small objects tend to cool rapidly
this knowledge was particularly useful in the manufacture of ornamental
shawl-pins and ear spoons and accounts for the higher percentage of tin
the Incas used in making them.
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Since these early metallurgists were unfamiliar with modern methods of
heat treatment they were compelled to sacrifice the extra hardness and
strength obtainable in casting axes and chisels by increasing the tin
content in them. Such implements had to be frequently hammered and
annealed. Since cold-working had to be depended upon to produce the
final hardness of such objects, more than one heating was needed in
forging the blades and this process necessitated a low tin content.
Necessarily they employed a formula for combined cooper and tin which
has impressed archaeologists only familiar with the chemical analysis of
Inca bronzes, as being that which is unsuited for axes, chisels and
large knives. It was only after a metallographic study of Inca bronzes,
involving the mutilation of the pieces examined that Professor
Matthewson learned the structure of such objects, the methods of their
manufacture and the reasons for the variation that has been found to
exist. The Inca metallurgists cast their bronze knives generally in one
piece and then cold-worked them.
Such reheating as took place was solely for the purpose of softening the
metal to facilitate cold-working, which was probably done at less than
red heat. Some Inca bronzes are found to have been repeatedly hammered
and reheated. This hammering might have been done with the stone tools
with which the Incas were familiar.
The knife blades appear to have been worked and hammered so as to extend
the metal more or less uniformly in several directions. Chisels and
axes, on the other hand, were cast practically in the shape finally
desired.
The Inca metallurgists were sufficiently ingenious to use more than one
variety of bronze in the construction of an inverted “T” . If it was
desired to ornament the of the handle with a llama’s head or attractive
bird, the ornament would be made of bronze with a content of tin. The
metal of the blade and the lower part of the handle on the other hand
was of bronze of lower tin content because the blades had to be
cold-worked.
The ornamental part of the knife handle was actually cast around the
shank of the knife handle was actually cast around the shank of the
knife after it had been completed. The Inca artisan, anxious to make a
good serviceable knife and at the same time make it attractive, had
learned over the centuries to take infinite pains in doing it. If he
wished to make a hole in the end of a knife or shawl-pin, he did it in
the process of casting because he lacked steel tools for drilling it.
In making bronze bolas which could be used in capturing a flying parrot
or many-hued macaw, he cast the ball with a pin already in so that the
cord connecting the two parts of the bolas could be securely fastened
without interfering with the smooth flight of the missile. The pin was
not set into the bolas but was cast in place. It must have been a great
sight to see an Inca hunter bring down a flying macaw with a skillful
swing of the little bronze bolas, discharging them at just the right
moment to entangle its wings and legs without damaging the beautiful
captive.
Some axe blades bear evidence that they were used upon stone. Their
structure shows severe damage of a character which could only result
from very hard usage. They were probably used in cutting square holes in
ashlars and in making sharp inside corners. It is difficult to conceive
of any stone tools that could have been used successfully for this
purpose. Some writers have assumed that the Incas use bronze implements
to a large extent in finishing their best stone work. It seems to me,
however, that even their best bronze was too soft to last long in such
activities. It is not likely that it was often so employed. Experiments
made in our National Museum have demonstrated that patience,
perseverance, elbow grease and fine sand will enable stone tools of
various shapes to work miracles in dressing and polishing both granite
and andesite.
However, it is reasonably certain that the Inca builders used powerful
little bronze crow-bars to get those ashlars in place which were too
heavy to be lifted by hand. Called champis, these bars were sufficiently
strong to be used in adjusting blocks of stone weighing ten or twenty
tons. In a tensile test, made under the direction of Professor
Matthewson, an old Inca champi of poor quality showed an ultimate
strength of 28,000 pounds to the square inch. We found by experiment
with a new bronze crow-bar of the same Inca metallurgists, it had still
greater strength. The Incas could have used their little crow-bars for
prying into place granite blocks weighing twenty tons without damaging
the champis.
Inca bronze included not only such tools as axes, knives, chisels, and
crow-bars but also such domestic utensils as tweezers, shawl=pins, and
large bracelets, spangles and bells. They even made ear spoons, the ends
of whose handles were often decorated with figures of humming birds.
Perhaps the commonest bronze articles made by the Incas were shawl-pins.
Early drawings made by the Spanish conquerors show these pins were
always used for fastening the front of the shoulder covering. This
custom is still common in the Andes and I have noticed in many cases the
head of the shawl-pins is made like a spoon. The Incas do not appear to
have been familiar with spoons. The heads of their shawl-pins, which
vary in length from three inches to nine inches, are very thin so that
the edges were fairly sharp and appear to have been used for cutting
purposes. As the Inca women were frequently occupied in spinning yarn by
means of a hand spindle, or in weaving textiles, they would have found
such little knives very useful and handy.
They made bronze mirrors similar to those found in ancient Egyptian
tombs. They even succeeded in making a concave bronze mirror which, when
polished the rays of the sun to be sufficiently concentrated on a bit of
cotton as to set it on fire. One cannot help being impressed with the
great skill of the Inca metallurgists and wondering how long it took
them to learn this art.
They also made bronze bodkins or large needles with eyes sufficiently
large to permit them to carry a fairly stout cord. Sometimes these eyes
were made by flattening the head to a narrow strip, drawing this under,
laying it against the shaft of the bodkin and hammering enough of the
sides onto it to secure it. This process would readily have been
accomplished by the use of one of the little braziers.
They made little bronze tweezers intended to take the place of the
modern razor. Highland Indians seldom have any hair on their faces. The
Incas were probably anxious to remove any stray hairs by means of
tweezers was even known amongst the tribes of Micronesia in the Gilbert
Islands before it was thought of in New York or Paris. It is evident to
the observer of manners and customs that the desire for beauty parlors
is nothing new under the sun.
Source:
‘Lost City of the Incas, The Story of Machu
Picchu and its Builders’ by Hiram Bingham
The American explorer who found the ruins of Machu Picchu in 1911.
Hiram Bingham at Machu Picchu
The inspiration for Indiana Jones?
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