Cecilia Gallerani, the famous Lady with an Ermine portrayed by Leonardo da Vinci at the end of '400 (perhaps 1498), It can be taken at typical Milanese model girl “alla moda” era.
The girl, that at the time of the painting had about fifteen years, shows in fact with a combing then in vogue (https://www.pilloledistoria.it/8127/storia-moderna/400-la-bella-acconciatura-della-dama-con-lermellino) and with only a jewel (synonymous with this most sober and refined than many of his contemporary ladies who are used to dress up so much more eye-catching).
The thin, white Cecilia's neck is surrounded by a necklace close around the throat and then allowed to hang on the breast, as was customary at that time many other girls her age are also unmarried, but the jewel of the material still remains a mystery.
What had made the blacks grains that make up the necklace that centuries later we can still see them on the Gallerani?
Various assumptions: black amber, onice, black coral and agate the most reliable.
Ve it is however also another, rather implausible, according to which it would be treated instead of simple grains of fragrant pasta, for which burst, full Renaissance, a craze on the part of men and women (Photo gives: onap-profiling.org).