A tattooed frozen mummy called Oetzi, discovered over 20 years ago, has long been known to boast some serious body art, and now researchers have found some fresh ink, reopening the debate about the role of tattoos in prehistoric times.

The 5,300-year-old mummified iceman was first discovered back in 1991 preserved in a glacier in the Italian Alps, the various tattoos on his body were obvious from the start. But it wasn't until recently that researchers at the EURAC-Institute for Mummies and the Iceman noticed new ink located on the lower side of Oetzi's ribcage, bringing the total number of tattoos to 61.

The discovery "was a big surprise because we didn't expect to see a new tattoo," Albert Zink, the study's senior researcher and head of the EURAC-Institute, told Live Science.

All 61 of the tattoos - amongst the oldest ever documented - are made of black lines, 0.7 to 4 centimeters in length and arranged in groups of two, three or four parallel lines. Most of the markings are found on Oetzi's lower back and the legs between the knee and the foot, but this newly-discovered ink on his ribcage has long been obscured because the mummy's skin has darkened so much over the years.

So to better quantify Oetzi's tattoos, the research team relied on sophisticated photographic technology that covers the entire electromagnetic spectrum, from infrared to ultraviolet light.

"Each shot was taken seven times, using a different wavelength each time. This enabled us to cover the different depths at which the carbon powder used for the tattoos had been deposited. The ultraviolet waves were adequate for the upper skin layers, whilst we resorted to infrared light for the lower layers," researcher Marco Samadelli, who created the technique, explained in a statement.

It's still unclear why Oetzi has so many tattoos, but researchers speculate that they may have a therapeutic, symbolic, or religious significance. For instance, many of the tattoos are located on the mummy's lower back and near joints - areas where Oetzi might have experienced pain. It's possible the tattoos served as some sort of medicinal form of acupuncture.

This new ink merely adds another piece to the puzzle.

The findings were published in the Journal of Cultural Heritage.

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