The strange habit of licking the end of a brush revealed new evidence about the life of an artist more than 900 years after his death.
Scientists have discovered tiny particles of blue paint accumulated in the teeth of a medieval German nun.
The rare particles of lapis lazuli probably collected when she touched the end of her brush with her tongue.
Researchers say that this shows that women were more involved in enlightening sacred texts than previously thought.
The team initially investigated health and diets in the Middle Ages. They set off to examine the bones of corpses in a medieval monastery in Dalheim, Germany.
The scientists analyzed the dental calculus – essentially the dental plaque that became fossilized in the teeth during his lifetime.
When they examined a subject's teeth, called B78, they ultimately revealed far more than what she had eaten.
According to radiocarbon dating, the woman lived between 997 and 1162 AD and was between 45 and 60 years old when she died. According to the authors, the woman was average in almost all respects – except for what was attached to her teeth.
When the researchers dissolved samples of his dental calculus, they could not believe his eyes. Hundreds of tiny blue particles became visible.
"The dental calculus is really cool, it's the only part of your body that fossils while you're still alive," said senior author Christina Warriner of the Max Planck Institute for the Science of Human History in Jena, Germany.
"During this process, it incorporates all kinds of debris from your life, so pieces of food get stuck, and that ends up being a time capsule of your life."
"We found starch granules and pollen, but what we also saw was this bright, brilliant blue – not just one or two small ore points, but hundreds of them.We had never seen this before."
Important scientific investigations were needed to find out what particles were made.
Finally, the scientists realized that they were dealing with lapis lazuli, a rare and valuable pigment from a mountain in Afghanistan.
The pencil would be powdered and mixed to make overseas – a living blue, so expensive that artists like Michelangelo could not afford.
It was used in Medieval Europe to decorate only the most valuable religious manuscripts.
So how did this rarer artistic material end up in the teeth of a rural German religious woman?
"Based on the distribution of the pigment in her mouth, we concluded that the most likely scenario was to paint with the pigment and lick the tip of the brush while painting," says co-author Monica Tromp, also from the Max Planck Institute in Jena.
The researchers say that only scribes and painters of exceptional ability would have been charged with the use of this highly prized pigment.
The finding indicates that women were playing a much more significant role in writing and illustrating manuscripts at this time than previously acknowledged.
Although there were female monasteries in this period, it was believed that less than 1% of the books could be attributed to them before the twelfth century.
Often women do not sign their names in books as a sign of humility, but the authors also believe that there was a strong male prejudice at the time, and women were essentially made invisible. The authors say their findings are helping to clarify things.
"She lived in Dalheim, you can still see the ruins of the female community, but there is art, books, just a fragment of comb, there are only a handful of references in texts," said Dr. Warriner.
"It was written out of history, but now we find another place where women were involved in artistic productions of which we had no idea."
Researchers are keen to develop the technique, believing that many other artists who worked with a variety of mineral pigments of the period could be identified.
"I think it would be an incredible opportunity to give identity back to these people, we lost all their individuality."
The study was published in the journal Science Advances.