Oil paint
The "Lady with an Ermine" was executed in oils on a small, 54 × 39 cm (21 × 15 in) walnut wood panel. Oil paint was relatively new to Italy at the time, having been introduced in the 1470s, and walnut was a wood favored by Leonardo, but not commonly used by other artists in Lombardy at the time. The wood is thin and about thick and is presumably from the same tree as the wood for his later portrait, "La Belle Ferronnière". The work is prepared with a layer of white gesso and a layer of brownish underpaint. The painting shows a half-height woman turned toward her right at a three-quarter angle, but with her face turned toward her left.