Mummification – whether that be through arid transformations in the desert or via the more famous embalming processes – isn’t straightforward. Depending on how it’s done, the resulting mummified person, or animal, can look quite different from the next.

This is no better epitomized than by a mindboggling discovery by Hungary’s University of Szeged. Recounting their research in a new study, the team focus on the tale of a weirdly colored, semi-preserved baby’s hand, found in 2005 in an abandoned cemetery in Nyarlorinc, a village in the south of the country.

The painstaking work took until now to find out why, unlike this hand, the rest of the baby – although variably green – wasn’t anywhere near as well preserved. As first elucidated by The New York Times, this investigation didn’t just solve a longstanding mystery, it revealed a new type of mummification technique too.

Writing in the journal Archaeological and Anthropological Sciences, the team explain that when the “minute remains” of the late-19th-century baby were found, the level of preservation was so good that a series of multidisciplinary investigations were ordered. Mummified human remains are actually rarer than you think, and these at a glance were already “unparalleled in the bioarcheological record.”

As emphasized by the team, mummification has a nebulous definition. It doesn’t refer to any one technique; rather, it’s describing any dead body with well-preserved soft tissues. This certainly applied to this long-gone baby – who was stillborn or died shortly after birth – but something was clearly off here. Why were the remains so green, and why was the baby's hand far better preserved than the rest of it?

Here’s where things get weird. Chemical analysis of the baby revealed that the concentrations of copper within the remains were a staggering 497 times higher compared to other mummies. In fact, they were the highest ever seen in a mummy.

Copper is occasionally found in corpses buried long ago. Whether they be coins or weapons, copper-rich materials are often included in the ritualistic disposal of human remains. Sometimes, as noted by The Smithsonian, this copper accidentally partially mummifies remains by infiltrating the skin and somewhat preserving it from microbial decay.

This baby, however, was impregnated with the stuff, especially one of its hands. After a closer look at the containers in which the remains were interred, it transpired that the baby was buried with copper coins. One was likely placed in its more mummified hand, which – as the coin leached copper over time – inadvertently helped preserve it better than the rest of the increasingly green child.

Copper alone isn’t enough to engender a “complete mummification process”; a relatively isolated setting prohibiting full decay is required too. In any case, the team note that this “may be the first solely copper-driven mummification case ever reported,” and it almost certainly won't be the last either.

Lead author Dr János Balázs, of Szeged’s Department of Biological Anthropology, told IFLScience that “pot or wooden box burials are known from archeological and ethnographical records.” This means that “similar cases of mummification may still occur in the future in Europe, or everywhere else where mortuary practices may have been in use producing similar microenvironments.”

Not everything’s been solved. Although the cemetery dates back to the Late Medieval, this individual was buried here at least 150 years after the site was abandoned – and it’s not clear why this happened. At the same time, although coins were once given to the dead as a way of helping them reach the afterlife, this fell out of fashion by the time this baby perished.

Either way, we’re sure the new discovery is likely to make other experts in the field green with envy.