Examination of the cross-sections has shown that in the earlier phase he used exclusively cobalt blue, available from 1802, his habitual choice during the 1870's and early 1880's, but in finishing and revising the composition he used only artificial ultramarine which came in use in the 1870s.
A common misconception with this is that nits and lice are the same thing. In fact this is not the case, the truth is: Lice are the tiny grey or brown insects that are found in the hair. The lice are about the size of a small seed (i.e. Sesame seed) and cling to the hair staying close to the scalp which they live off.
Head lice are parasitic wingless insects. They live on people's heads and feed on their blood. An adult louse is about the size of a sesame seed. The eggs, called nits, are even smaller - about the size of a knot in thread. Lice and nits are found on or near the scalp, most often at the neckline and behind the ears.