Obsidian: The Smoking Mirror
Blog post by Linda Coulson, SDAC Volunteer
Obsidian is a beautiful and highly functional material that is one of the few substances utilized by humans throughout history (Ryan 2024). It is a material that is found within the artifact collections of curation and museum facilities around the world, including the San Diego Archaeological Center. Gaining knowledge into how obsidian was used in the production of tools, weapons, ritual items, jewelry, and trade has contributed to our understanding of many ancient cultures around the world. Among these cultures were the ancient Egyptians, the ancient Greeks, the Mesopotamians, the Aztecs, the Mayans, the Incans, and Native Americans. The increasing focus by modern peoples on the repatriation of their cultural artifacts, including obsidian objects, reflects the irreplaceable power of these artifacts to illuminate a unique culture’s history. It seems like the stories of how obsidian has been used throughout history are stories worth telling.
The Basics
Obsidian is often called a rock, but it is actually a volcanic glass, typically black in color. It forms in a very particular way, which gives it unique physical properties. These properties are what distinguishes obsidian from other materials and makes it useful for a multitude of purposes, including crafting everything from tools and weapons to spiritual objects and jewelry and, perhaps most amazingly, to make surgical equipment. The importance of these obsidian objects is reflected in their inclusion in many graves, including those of presumed elites of their community. The technological development of various peoples can be traced through the gradual refinement of their obsidian objects and how they are used (Hulatt 2024).
When a volcano erupts, molten rock, or magma, is thrown out of the volcano. As the magma leaves its underground inferno and finds its way to the surface, it starts to cool and become solid material. What kind of solid material depends on how fast the cooling happens. If it cools slowly, crystals are able to form and we get rock with very visible crystalline structures, such as quartz. If the magma cools rapidly as it hits the surface air or water, crystals do not have a chance to form and instead we get a thick and sticky material. As cooling proceeds, this becomes a smooth and glassy structure with no visible crystals. This is obsidian. Therefore, despite their similar chemical composition, (70-75% silicon dioxide) the differences in cooling rates lead to very different-looking material. 
Because of the lack of crystal formation, obsidian presents as a hard and brittle material that, when it breaks, creates exceedingly sharp edges, as thin as a single atom (newstoneagecabochons.com). This is among the sharpest edge known to humankind, while at the same time forming a smooth and curved surface. This means that obsidian can be carved very much according to the wishes of the stoneworker, or flintknapper, rather than according to any internal properties of the material, such as its crystal formation (Glascock 1994; geologyscience.com modified 2025).
The process of flintknapping with obsidian (or other types of stone) requires a good deal of skill, which in its prehistoric uses was likely passed down through generations. Knappers would use a heavy stone like a hammer to hit a large unworked, or core, stone. The force (sometimes called percussion) created by the hammer stone hitting the core rock causes a flake of stone to peel off from the core. Flintknapping involves repeating this reductive technique over and over to remove many flakes from the core stone. A smaller instrument such as a bone or antler can then be pressed along the edge of a flake to force off yet a smaller flake (pressure flake) in order to sharpen the edges and thin the original flake, making it into a functional tool (Wallace 2021). Since obsidian lacks an interfering crystalline structure, it breaks in a predictable and controlled way, which helps the knapper create a sharp, useful tool. It is because of this important breakage property that obsidian became perhaps the most highly prized of prehistoric material for stone (lithic) tool production (Dietler 2004).
What makes obsidian especially notable is its striking jet-black coloration. Just as the color of stained glass is created by adding a substance to molten glass, the black color of obsidian is naturally created through the presence of iron oxide minerals distributed throughout the otherwise clear glass.
Obsidian’s unique physical characteristics, including its razor-sharp edges, striking color, and relatively easy workability, greatly contributed to the large variety of uses to which it was put across the centuries. For example, obsidian has been utilized in the manufacture of cutting and piercing tools, weapons, and hunting implements such as knives, arrowheads, and spear points. In addition, obsidian has also been the centerpiece in the creation of jewelry and art, sometimes for spiritual and ceremonial purposes. Its deep black color suggested a connection to the night, and in some cultures, its mirror-like qualities suggested a path to the underworld. But obsidian’s uses do not end there! Here are several ways that brilliant people have taken advantage of obsidian’s unique properties.
Surgical Scalpels
Many years ago, a Yale University expedition to the Andes Mountains — the same expedition that first brought Machu Picchu to the attention of the rest of the world — discovered a rare Incan skull. This skull had five perfectly circular holes of the same size cut through layers of healed bone. Since that initial find, many other Incan skulls with similar holes have been discovered. The procedure of drilling into skulls is called trepanation, and among the Inca people, the only material that could have been used for this is obsidian.
While the process seems clear, what remains unclear is why some of the excavated remains have so many holes. Various theories have arisen to try to explain this phenomenon, including that it was part of ritual practices. If that were the case, though, the holes would have presumably been placed in the same locations on each skull, as if certain locations held particular significance. But there are different numbers of holes in different locations on each skull, making it unlikely to be the result of some overriding ritual. So, if not for ritual purposes, why are there multiple holes in some of these Incan skulls?
John Verano, a forensic anthropologist, researched this question for over 25 years, and he advocates for another theory. He suggests that the holes were created by prehistoric Incan surgeons in order to relieve symptoms of head injuries, such as headaches and dizziness. Some of the patients would survive the trepanation procedure, their skull would heal, and it might stop there. But maybe it did not work — some patient’s symptoms might continue or return, and they would come back for more treatment, perhaps numerous times. Thus, some of the skulls have as many as seven holes with healed bones, which means the patient survived the procedure seven times.
This work of prehistoric Peruvian surgeons is a remarkable achievement that could not have been accomplished without an essential tool, an incredibly sharp obsidian blade. It could make possible the precise, clean cuts necessary for such a delicate procedure, such as no other tool of the time could have.
Our story moves to Canada and to Dr. Lee Green of the Department of Family Medicine at the University of Alberta. Dr. Green is among a number of surgeons in the United States and Canada, who use obsidian for scalpel blades. Obsidian can produce a cutting edge many times finer than even the best steel scalpel. As Dr. Green explains, “’The biggest advantage with obsidian is that it is the sharpest edge there is, it causes very little trauma to tissue, it heals faster, and more importantly, it heals with less scarring’” (Bonifield 2016; Buck 1982; Ryan 2024). It is astonishing to think that a medical procedure as delicate as neurosurgery was performed hundreds or thousands of years ago, utilizing a technology that is, to some contemporary surgeons, superior to modern surgical counterparts.
The Smoking Mirror
Aztec culture imbued obsidian with great significance. Their supreme god, Tezcatlipoca, (whose name means “smoking mirror”) was pictured with polished black obsidian mirrors above his head or elsewhere around his body, designating him as the lord of the night and its creatures. In keeping with Aztec beliefs in the power of obsidian mirrors, large pieces of obsidian were thus polished in order to become highly reflective (though dark) surfaces. These mirrors were thought to be portals into the realm of Aztec ancestors and their gods and became highly valued objects, particularly for Aztec elites, for the purpose of divination (getty research institute; newstoneagecabochons.com). They seemed to be equally prized by the Spanish conquistadors, who absconded with them and brought a few back to Europe. One of them fell into the hands of John Dee.
John Dee was a rather fascinating individual of the Elizabethan world, and his use of obsidian was at the center of his unusual life. He was a court astrologer and scientific advisor to Queen Elizabeth I from 1558 to the 1570s and also was considered a brilliant mathematician. But beyond even those roles, John Dee led a life filled with intrigue and mystery. He was considered by some to be a deluded man who dabbled in alchemy and attempted to communicate with angels, while at the same time viewed by others as England’s foremost scientist. Dee signed his letters to Elizabeth I as ‘007’, the two circles symbolizing that the document was meant for Queen Elizabeth’s eyes only while the seven was a lucky number for alchemists. Centuries later, Dee’s signoff would be used by Ian Fleming in his James Bond novels. Also, Dee became involved in developing secret codes and played a crucial part in what would later become the British intelligence service. While at a university in the Netherlands, Dee studied the occult, but this was not unusual for intellectuals of the time, for whom science and magic were part of their attempt to understand God. He accepted heliocentrism, the then controversial theory that all the planets revolve around the Sun, and he is credited with developing the navigation systems that helped to establish England’s naval superiority. Whether through casting a spell or his knowledge of meteorology, Dee was able to predict the storms that devastated the Spanish Armada and allowed the English navy to defeat their enemy’s superior forces (historyextra.com 2021).
As part of John Dee’s study of divination and the occult, he attempted to talk to angels and predict the future. Dee’s process included the use of mirrors and crystals, and so an obsidian mirror evidently came into his possession. His “spirit mirror” was comprised of a black, nearly circular piece of obsidian that was polished on both sides to produce deep dark reflective surfaces. The fact that the mirror was of a novel material (at least to Dee and his Elizabethan contemporaries) was derived from an exotic culture, and presented with dramatic, dimly reflected images must have intrigued Dee. One can imagine him staring into the dark depths of the mirror, seeing spectral images dancing around and pleading with them for answers about the afterlife and deeper mysteries of the universe.
John Dee’s mirror is now in the possession of the British Museum in London and has been studied along with other obsidian objects in the museum’s collections. In order to identify the original volcanic source of the obsidian comprising Dee’s mirror, researchers used an X-ray fluorescence scanner to measure the chemical composition of his mirror and compared these results to the chemical makeup of obsidian originating from a geological source in Mexico. Building on this information, the researchers were able to determine that Dee’s mirror came from a site just northeast of Mexico City, an area that would have been under Aztec control in the early 16th century.
Clearly, obsidian objects such as John Dee’s mirror would have been part of the flow of goods from the New World to Europe following Columbus’s voyages. Such objects held a great fascination for the scholars of Europe during the period, perhaps without them truly understanding their significance. In the case of John Dee, he may have understood the reverence held for obsidian mirrors within Aztec culture and chose to possess one precisely because of its perceived powers (Campbell et al. 2021; britishmuseum.org; Gershon 2021).
A Blank Canvas
It is difficult to know generally how much knowledge these late 16th- and early 17th-century Europeans would have had of the original Aztec meanings of their newly acquired obsidian objects. What we do know is that their use in European cultural pursuits evolved in most interesting ways.Perhaps most interestingly, obsidian mirrors and other obsidian surfaces came to be used as ‘canvases’ by some European painters, including the Spanish artist Bartolomé Esteban Murillo. Murillo was one of the most popular religious painters of 17th-century Spain and his chief patrons were the religious orders. He worked almost entirely in Seville, an area which was heavily involved in trade with the New World, including the importation of obsidian. Two of Murillo’s works, Agony in the Garden and Penitent St Peter Kneeling Before Christ at the Column, which have been hanging in the Louvre museum since 1785, have always stood out from his other works because of their black, glassy, stone backings. In 2007, an x-ray spectrometry analysis of these two paintings brought an unexpected result. It was determined that Murillo’s works were actually painted on obsidian slabs originating from geological sources in Mexico. Since the two obsidian backings vary somewhat in physical appearance, one could speculate as to why these two particular pieces of obsidian were chosen by the artist. It is possible that the visual appearance of the obsidian influenced the subject matter of the artwork in some way. For example, in the case of his Agony in the Garden (probably dating from the late 1600s), Murillo’s facility with light and dark is very evident, and importantly, he used an imperfection in the blackness of the obsidian backdrop. This imperfection came in the form of white streaks used to create an image of dawn breaking on the black backdrop. Murillo did leave a large part of the backings in reserve, which allowed the obsidian to be revealed over three-quarters of the visible surface of the paintings (Masley 2001; Pixley 2012; Calligaro 2007).
How Obsidian Trade Changed the World
Among obsidian’s many valuable and unique functions through time, including production of tools, weapons, hunting implements, art, jewelry, and ritual objects, there is one that has placed obsidian at the center of archaeological and anthropological studies all over the world. This is its role in the development of trade and trade networks. There are several factors that have contributed to this. First, obsidian has always been highly prized for its unique physical properties, which make it enormously functional and a resource that was always in great demand. Obsidian was so highly valued that societies were willing to incur enormous cost to obtain it, even if it meant transporting it over great distances from its original geological source. We know this because obsidian can be traced through chemical analysis from its found location back to its source, making it possible to determine how far it traveled (as in the case of Dee’s mirror). Additionally, obsidian is far more durable than ceramics or fabrics or other archaeological materials so its use in studying trade is much more efficient and observable.
Evidence of long-distance obsidian trade has been connected to many of the world’s earliest civilizations dating back some 16,000 years. Trade, and particularly long-distance trade networks, were so vital to communities because with trade came an exchange of ideas, technologies, and possible social interactions between very different and far-reaching groups of people. This led to more complex societies with the creation of social hierarchies, including an artisan class skilled in producing the needed obsidian objects for trade. With these advances also created an enhanced elite class that was wealthier and more privileged with more political power within some societies. Possession of more obsidian became a status symbol which was carried to the grave (mexicohistorico.com; Stemp et al. 2019; Day).
Its impossible to know for certain how different the past and the present might have been without the existence of obsidian, but it is certain that obsidian contributed significantly to how our past and present have come to be.
References
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