Laser-Stimulated Fluorescence Unveils Intricate Mummy Tattoos
Art by Luna Aguilar
I already know what you’re thinking. Laser fluorescence? Intricate mummy tattoos? This sounds like an integral plot point in Indiana Jones and the Temple of Doom. You aren’t wrong, but stay with me here.
It turns out that many mummies have tattoos. Across numerous cultures, tattooing is and has been an important mode of expression. The oldest identified mummy tattoo dates back to ancient Egypt, circa 3100 BCE. Analyzing these tattoos gives us unique insight into the culture from which they came. They were important status symbols, art forms, and even therapeutic practices. The problem, though, is that as skin degrades, so does the visual quality of the tattoos within. Because of this, anthropologists run into a host of problems when studying tattoos. In the past, they generally used infrared and white light imaging to examine tattoos on preserved human remains. While better than the naked eye, even the best imaging left something to be desired. The images were still blurry and lacked the fine detail of a fresh tattoo on living skin, so anthropological insights were slightly obscured.
This is where lasers come in. Laser-stimulated fluorescence (LSF) is a non-destructive technique, most commonly used by biologists, that employs a high-power laser to excite molecules, causing them to emit light through the phenomenon of fluorescence. A camera records the fluorescent light to reveal hidden details that evade typical imaging techniques. The advantages of this technique have paved the way for advances in other fields too. In paleontology, it has been used to reveal hidden muscle patterns and feather imprints that provide valuable information about the soft matter that does not usually reveal itself in the fossil record. In medical research, the technique has been used to differentiate diseased cells from healthy tissue. In forensic sciences, it shows traces of fluids and bruises hidden to the naked eye. The list goes on—long enough it even includes mummies.
Michael Pittman, a dinosaur paleobiologist at the Chinese University of Hong Kong, had been using this technique in his research for years. In 2022, Pittman, among other researchers, expanded the reach of LSF imaging to examine ancient Roman artifacts. In the study, they used LSF imaging to reveal faded paintings and fingerprints on preserved pottery. They went on to speculate in writing that this technique would be useful in other archaeological studies.
“A Polish colleague, Judyta Bąk, saw my paper and asked me the question: ‘Could this technique work on mummified human remains?’” Pittman said. “We hypothesized that because human skin glows under laser light, and anything on it that isn’t human skin glows less, more, or not at all, that would give us a nice contrast to develop an image.”
Bąk noted that the core components of ancient tattoo ink supported the base of her hypothesis. If this ancient tattoo ink is composed primarily of carbon, as most ink is, they would expect it to glow less than mummified human skin. This gap in fluorescence should allow them to create a beautiful, clear image of details hidden from the human eye, one clearer than those seen with previous techniques. With these ideas in mind, the researchers flew to Peru to test their hypothesis.
The team obtained access to mummified people from the Archaeological Museum of the José Faustino Sánchez Carrión National University of Huacho, Peru. These mummies were from the pre-Columbian Chancay culture, which developed along what is now the central coast of Peru between approximately 900 and 1533 CE. Much of what scholars know about the Chancay people comes from rich remnants of their art through textiles, pottery, and woodwork. Their textiles draw the most attention, as many of them are painted with complex figures and geometric patterns. Scholars also know that tattooing was common in Chancay culture, but ancient tattoo specimens have degraded over time. Because of this, it is difficult to learn about the artistic qualities of the tattoos or to ascertain how the process through which they were made.
The researchers performed the standard white-light and infrared imaging, and then they used LSF imaging on the tattoos and compared the results. The 0.1 to 0.2-millimeter detail revealed by the LSF imaging showed that each ink dot was placed by hand–a technique that requires great skill and precision. With this technique, the ancient artists produced magnificent, complex, geometric, and zoomorphic patterns. The imaging also revealed that the object used was likely finer than modern tattoo needles, likely a cactus needle or sharpened animal bone. With needles so fine, little pressure was needed to apply the art to the skin.
This fine level of detail revealed by the LSF imaging could be crucial for anthropologists looking to decipher ancient tattoos and the methods used to create them. In this instance, the detail and complexity uncovered by Pittman and his team seem to exceed that of other Chancay cultural artifacts, including their pottery, textiles, and rock art. This confirms the centrality of tattoos in Chancay art, although further research is needed to place these empirical observations in a social and historical context. Interestingly, not all tattooed individuals showed signs of the fine tattooing technique, possibly indicating divisions in tattooing practices among the population. Whatever the case, the success of this team’s efforts suggests that this technique could be successfully applied to mummies from other historical settings.
“In these Peruvian mummies, because it’s on a coastal location that’s very dry, even though it’s about a thousand years old, it is still very well-preserved,” Pittman said. “Even if we found a mummy that was ten thousand years old that was beautifully preserved and dried up, there’s no reason to say that LSF wouldn’t work then.”
LSF imaging does have its limitations. Even though it can uncover details past what is visible, degraded tissue from poorly preserved individuals is less likely to present the same image quality. Nonetheless, Pittman and his team are hopeful that the technique will have broad applications and allow anthropologists to uncover even more about ancient groups of people and their cultures worldwide.