All About Glass

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Pre-Columbian Use of Obsidian

All About Glass

The lack of any advanced metallurgy among the Aztecs and Mayas has long been a mystery to students of pre-Colombian civilizations. Why, historians ask, were the great Mexican empires stuck in the %%Stone%% Age?

The Spanish crushed the Aztec empire with amazing ease, and the Americans' technological inferiority was undoubtedly partly responsible. The conquistadors had gunpowder and horses; the Aztecs had neither. However, blades of the Aztecs swords, made of obsidian, were sharper than steel. They could behead a horse.

%%Obsidian%% is a kind of glass formed during volcanic eruptions, and it shares all of the basic physical properties of ordinary glass. The fact that the edge of a newly chipped flake is sharper than surgical steel was only discovered in the 1970's, and it has led to the use of %%obsidian%% blades in eye surgery, since the evenness of their cut permits much faster healing. The Aztecs called their %%obsidian%%-edged sword macuahuitl. Usually the swords were lined with ten blades; five on each side. Because %%obsidian%% is glass, it naturally fractures into a sharp, even, predictably shaped blade when chipped. Also because it's glass, it is brittle and cannot be resharpened. The blades on swords undoubtedly had to be replaced after a few uses; this is the main reason steel eventually supplanted %%obsidian%% after the Spanish conquest.

Why didn't the Aztecs fare better against the Spanish with such effective swords? Probably. Their swords didn't have tips and were not meant to pierce; they were designed only for slashing. An adept swordsman could fend off an Indian simply by ducking a swing of a sword and then running the enemy through.

%%Obsidian%% was used extensively among pre-Colombian societies throughout North and South America, but it reaches its highest development at the hands of the Aztecs. They used the blades for both hunting and warfare. %%Obsidian%% provided the projectile points for spears and arrows. %%Obsidian%% tools were used to shape the shafts of spears, arrows, and swords. %%Obsidian%% knives cut feathers and the cotton thread out of which mantles bestowed on successful warriors were made. The glass was used in butchering and in sacrifice. It was even used to cut a stillborn child into pieces before removal from the womb. And the versatility of %%obsidian%% made it a prized trade item.

The extreme sharpness of %%obsidian%% blades may help to explain why the Aztecs were willing to submit to self sacrifice. They cut their tongues and ears with %%obsidian%% blades on ritual occasions, caught the falling blood on the index finger, and flipped the blood in the direction of the sun or the moon. Such self-mutilation was formerly believed to be quite painful, but it is now understood that a fresh %%obsidian%% blade is so sharp one can barely feel a cut into the flesh. In fact, the very sharpness of the %%obsidian%% blade is probably the primary reason the Aztecs had no metallurgy. To develop a metal that could do the things %%obsidian%% already did so exceedingly well would have taken too long. After the conquest, the Spanish adopted %%obsidian%% for many of their own tools, including shaving blades. It was not until the late 1700s that steel completely replaced %%obsidian%% in Mexican technology.

Another reason the Aztecs didn't look beyond %%obsidian%% was its sheer abundance. More than fifty ancient sources of the material have been identified in Mexico and Guatemala, and they are the densest deposits in the world. The Aztecs usually drew %%obsidian%% from one mine at a time until the source was exhausted, then they moved to the next. They surveyed for %%obsidian%% and other essential rocks by watching the early morning mists rising from the earth and searching for the stones where the mists were densest. If and why this worked is not clear; perhaps the ground was cooler and retained less moisture where there were mineral deposits, and so condensation would be greater.

%%Obsidian%% is a semiprecious stone that can be polished, which also contributed to its unchallenged importance. The Aztec aristocracy wore %%obsidian%% jewelry; priests and nobles used highly polished %%obsidian%% mirrors to divine the future. In their animistic culture, everything, including rocks, had a spirit, and %%obsidian%% was especially revered. The principle god influencing life on earth, Tezcatlipoca, had an obsidian mirror in place of one foot. An %%obsidian%% knife placed in water in the courtyard of one's home was believed to keep away sorcerers by frightening them with their own reflections. An %%obsidian%% blade was tied around the neck of a pregnant woman to prevent her child from being born harelipped.

For the Aztecs, obsidian was not only almost ideally suited to all its practical uses, it also had roles in society that transcribed the purely practical. It is almost impossible to imagine such a civilization forsaking this magical, useful, and abundant glass in favor of its methodical development of common metals.

By permission: Terry Stocker. "A Technological Mystery Resolved" American Heritage of Invention & Technology, Vol. 2, No. 3, Spring 1987, p.64. 

Published on December 1, 2011