This obsidian pressure blade from Mesoamerica likely dates to the Classic period, ca. 1000-1700 BP.  Obsidian pressure blades were a fundamental tool to the Mesoamerican city-states that arose from ca. 2500 BP, and their manufacture continued after the Spanish conquest.

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This obsidian blade has a single-facet unprepared platform.  The blade is unusual in that it propagated at a lateral angle to the platform, rather than at 90 degrees to the platform.  This suggests a ‘sideways flick’ on the part of the blade-maker.  The blade was removed relatively early in the pressure blade reduction process as indicated by the wide scar at the distal end of the blade, probably created in initial core preparation.

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In archaeological terminology, a ‘blade’ is a flake struck down parallel ridges on a core face, and measures at least twice as long as it is wide.  The edges of the blade are approximately parallel.  The core face is maintained by prior removals, and blades are struck off in series.  If they are struck from one platform, the removals are ‘unidirectional’, and if they are struck from two opposed platforms, they are ‘bidirectional’.  Blades were struck by direct percussion (using a hard or soft hammer) or indirect percussion using a punch; or they were pressed off using a pressure technique.  This involved placing the end of the indentor onto the platform edge and applying a load—either by hand or using a lever—until the crack initiated.  The placement of the indentor and the amount of applied force can be precisely controlled, resulting in extraordinary control of the size and shape of the resulting pressure blades.  A common approach was to set up the core so that most of the blades had a trapezoidal cross section; these are called ‘prismatic’ blades.  One of the trickiest aspects of pressure blade-making is securing the core, and experimental flintknappers have devised various ways to do this.  Pressure blade-making was famously explored by the experimental flintknapper Don Crabtree in the 1970s.

In the Tehuacan Valley of southern Mexico, obsidian pressure blades were made with unprepared platforms in the Abejas phase (ca. 4300-5400), with prepared platforms appearing in the Purron and Ajalpa phases (ca. 2800-4300 BP).  These dates indicate that blade technology was invented and became important during the Late Archaic period, and long-distance trade in obsidian was established in part to support blade-making technology.  Obsidian pressure blades appear frequently at sites across Mesoamerica after about 3000 BP and are ubiquitous from about 2200 BP.  The pressure blade cores across Mesoamerica are technologically similar, usually consisting of single-platform conical cores with blades removed unidirectionally from around the perimeter.  Archaeological and experimental research show regional and chronological variations in reduction, with different foot-held and hand-held core reduction methods developing.  A significant technological shift occurred ca. 1400-1500 BP in some regions, when core platforms were prepared by flaking followed by light pecking and partial or complete grinding of the surface.  This induced microfractures into the platform and made blade removal easier because the crack could initiate on a pre-existing micro-flaw induced into the stone.  The sizes of the pressure blades depended on the sizes of the obsidian available to the blade-making specialists.  Large obsidian macroblades were also made by hard-hammer percussion in Western Mexico, and the early stages of creating blanks for pressure blade cores were accomplished by percussion.

Pressure blade-making was a recurrent feature of the various complex states that arose in Mesoamerica with the advent of intensive agriculture.  Extensive markets developed for the trade in obsidian beginning during the Middle Formative period, ca. 2500-2900 BP.  Specialist blade manufacture was practiced by the Olmecs at Chalcatzingo during this period, and specialist blade-makers were a key feature of later Mesoamerican civilisations in Central Mexico, Oaxaca, West Mexico, and the Maya region.  The demand for pressure blades was intense as these tools were fundamental to completing the daily tasks of people living in these regions.  Up to 80% of the stone tools recovered by archaeologists in household sites in some areas are composed of pressure blades.

Blade production involved two sets of specialists: those located at the obsidian sources who mined the material and roughed-out the cores, and those located in more distant production centres who received the cores and produced the finished blades.  One archaeologist suggests that if the blade-making specialists averaged the reduction of one core per day, they would have produced between about 48,000-54,000 blades per year.  In the historic period, the blade-makers were itinerant craftsmen who travelled between markets.  Blades were hand-held or were elements combined into composite tools and weapons, such as the famous macuahuitl sword encountered by the Spanish invaders.  Although copper and bronze appeared ca. 1000-1200 BP, it was rarely used as tools, and obsidian pressure blades were made and used into the historic period, ca. 500 BP.

Pressure blades in Mesoamerica were almost always made of obsidian, and the cosmological significance of this material likely enhanced the popularity of these blades.  For the Aztecs, obsidian (called itztli in Nahuatl) was a combination of of cosmic forces with earthly ones.  Obsidian (and chert) was considered by the Aztecs to be of celestial origin, but resided below the earth’s surface.  The Maya believed that obsidian was formed when lightning struck the earth.  This correlation between the cosmos and earth was enhanced by the star- or sun-like iridescence of some varieties of the stone, combined with the way that it was extracted from underground mines.  The reflective quality of obsidian was also important to the Aztecs; the god Tezcatlipoca observed the world by its reflection in an obsidian mirror, and obsidian thus became a metaphor for the power of the Aztec rulers.  Obsidian transcended the Aztec physical and spiritual worlds, and three of the nine levels facing souls on their journey to Mictlan involved obsidian; in one level it was necessary to face an icy obsidian-bladed wind.  Obsidian is also linked symbolically to the Aztec warrior goddess Itzpapalotl, or ‘Obsidian Butterfly’, who ruled over the souls of children who died in infancy and women who died in childbirth.  Her wings were covered in obsidian blades and white flint knives, called tecpatl.  When a person in Mesoamerica made or used an obsidian (or chert) knife, it was in a symbolically-charged context.

Traditional methods of making obsidian pressure blades were observed and described by an unknown Spanish traveller in Central Mexico in ca. 1520.  The blade-makers used a wood shaft called an itzcolotli that rested against the belly at one end.  Attached to the shaft was an L-shaped piece which was set against the core platform.  The blade-maker sat on the ground and held the core between his feet, probably with a backstop to prevent the core from moving forward.  Inward pressure was applied by the stomach muscles and outward pressure was applied by the arms lifting upward until the blade detached, flew through the air, and landed in front of the blade-maker.  The traditional itzcolotli blade-making method was reconstructed by modern flintknappers Gene Titmus and John E. Clark after years of painstaking trial-end-error research.  They found that it was possible to remove pressure blades measuring 23 cm long using this method.