Anita Radini, an archaeologist at the University of York, in England, spends a lot of time looking at tartar. Really old tartar.
Tartar, or dental plaque — that film of bacteria that feels like sweaters on your teeth — contains a wealth of information about what long-dead individuals encountered in their daily lives. Dr. Radini has seen all sorts of things trapped in it: food particles, textile fibers, DNA, pollen, bacteria and even wings of tiny insects.
But several years ago, when studying the dental plaque of a nun from medieval Germany, Dr. Radini saw something entirely new: particles of a brilliant blue. She showed the findings to Christina Warinner, another tartar expert, who was shocked.
“They looked like little robins’…