Despite the extraordinary level of detail, the drawing and the skull both feature the same small anatomical errors, further strengthening the link with Leonardo.
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Chemical analysis showed the artifact was made from an agate-based mixture of quartz and gypsum. Leonardo invented this mixture, which he called "mistioni," between 1503 and 1509. No one else is known to have experimented with this material, which was likely sourced in a mine near Volterra in Tuscany.
The size of the artifact match Florentine measurement units that were used in the Renaissance. "The origin of the skull, leads, therefore, to Florence," Missinne said.
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Contemporary writings such as those in the inventory of Da Vinci's assistant Salai confirm Leonardo's possession of a detailed miniature skull made from mistioni.
The skull dates to about 1508, Missinne said, when Leonardo was 56. Missinne believes the aging artist, who was prone to being melancholic, used the skull as his personal sorrow stone.