Atop the terrace of the Temple of the Sun, a multi-sited wall called Ollantaytambo rests. Its reflective surfaces must have gleamed in the sunlight as the ancient people went about their worship activities. This location has a wide selection of different types of rock: andesite, basalt, pinkish porphyry, and diorite. Like in many other walls and temples, the stone joints have been vitrified so they reflect light. The effect is especially prominent wherever rocks have fallen out or been removed from the structures. It becomes obvious that the adjoining faces of the stones were vitrified before they were fitted together perfectly. This must have had some practical purpose as it was not usually done to visible surfaces. Those were polished in more mundane ways but not vitrified to create that extremely reflective surface. Although archaeologists see it as an aesthetic trait now, perhaps it was purely functional all those centuries ago. Also, because it occurs only on interior touching surfaces, it is obvious that vitrification was done artificially in some way and not a result of, for example, a wildfire or lightning strike.
As interesting as the vitrification of the stone is, researchers disagree on one very important factor. Some argue that the vitrified layer is not part of the original stone at all. Instead, they believe it is a different type of material that was layered on top of the stone as a form of mortar or cement. It is difficult to figure out what the truth is on these ancient structures. From the research that has already been done, the layer seems like the stone but has undergone some sort of chemical transformation. Another sign that points to a more natural explanation is that some parts of caves and tunnels that have not been changed by human hands also show signs of vitrification.
The steps leading to the Temple of the Sun were vitrified on many surfaces. Other parts were polished in ways that archaeologists recognize from the civilizations that made it. Scientific study of the materials themselves has not been done in any great measure. Above Cusco lies a place of archaeological interest with considerable number of caves called Tetecaca.
Scientists from a university in Holland were able to take microscopic photographs of the stone itself in order to solve this mystery once and for all. They found that the regular stone and the layer that had been vitrified were distinctly different in makeup. However, they also found a thin layer between them that showed a granular transition from one state to the next. Just like you would see charcoal change to charred wood change to unburned wood on a log that had been in a fire, so too did this vitrified stone show three distinct layers. This demonstrates that the vitrification was not a part of something applied to the top of the stone.
When studied chemically, some differences in the makeup of the stone are also noted. The vitrified layer contains elements not normally found in the type of stone used for the block. Mostly, there was evidence of higher amounts of silica, which seem to point to an application process or a chemical or heat process that cannot truly be explained knowing the technology of the time. Melting or chemically changing the stones with heat would require some type of furnace that operated above 1000 degrees Celsius or extremely high pressure. How these ancient people could do such things is beyond the understanding of modern archaeologists.
Vitrification of stone used in early civilization building sites has been found throughout Cusco, Chinchero, Tambomachay, and surrounding areas.
Archaeologists have also found evidence of this unique and mysterious process at Machu Picchu. In some locations, it seemed to be quite a popular way to create stunning reflections of light and shadow on walls and temples. In other locations, such as the Temple of the Three Windows and the Main Temple plaza, it served a more functional purpose on the stone surfaces that touched at the joints.