Radini and her co-author, Christina Warinner, did not set out to study the production of illuminated manuscripts. Radini, now at the University of York, was initially interested in starch granules in tartar as a proxy for diet, and Warinner, a microbiome researcher at the Max Planck Institute, wanted to study the DNA of ancient oral bacteria. But the blue particles were too striking to ignore.

“Can you imagine the kind of cold calls we had to make in the beginning?” says Warinner. “‘Hi, I’m working with this thing on teeth, and it’s about 1,000 years old, and it has blue stuff in it. Can you help me?’ People thought we were crazy. We tried reaching out to physicists, and they were like, ‘I don’t know what you’re talking about.’ We tried reaching out to people working in art restoration, and they were like, ‘Why are you working with plaque?’” She eventually reached physicists at the University of York who helped confirm the blue did indeed come from the mineral lazurite, derived from lapis lazuli.

But art experts were still skeptical. Some dismissed the idea that a woman could have been a painter skilled enough to work with ultramarine. One suggested to Warinner that this woman came into contact with ultramarine because she was simply the cleaning lady.

Warinner eventually reached out to Alison Beach, a historian at Ohio State University who studies female scribes in 12th-century Germany. Over the past couple of decades, Beach and other scholars have cataloged the overlooked contributions of women to medieval book production. The challenge, Beach says, is that while most manuscripts with signatures are signed by men, the vast majority of manuscripts are unsigned. But a small number of surviving manuscripts are signed by women, and scholars have found correspondence between monks and nuns about book production.

Beach even came across a letter dated to the year 1168, in which a bookkeeper of a men’s monastery commissions sister “N” to produce a deluxe manuscript using luxury materials such as parchment, leather, and silk. The monastery where sister “N” lived is only 40 miles from Dalheim, where the teeth with lapis lazuli were found. Beach also identified a book using lapis lazuli that was written by a female scribe in Germany around a.d. 1200. The pigment would have traveled nearly 4,000 miles from Afghanistan to Europe via the Silk Road. All the evidence suggests that female scribes were indeed making books that used lapis lazuli pigment in the same area and around the same time this woman was alive.

The team considered a number of alternative ways lapis lazuli could have gotten into the woman’s dental plaque. Could the particles have come from repeated kissing of an illuminated manuscript? This practice didn’t become popular until three centuries after this woman likely died. Could it have come from lapis ingested as medicine, as suggested in Greek and Islamic medical texts? There’s little evidence that prescription was followed in 12th-century Germany. The lapis lazuli particles were also especially fine, which requires a laborious grinding process. This detail in particular suggests that the stones were purposefully made into pigment.