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.
Nits are found firmly attached to the hair shaft about 1/4 inch from the scalp. They are oval and usually light colored or white, and take about a week to hatch into a baby louse called a nymph, then take about seven days to mature. Adult lice can live up to 30 days on a person's head, if the lice falls off a person, it dies within two days. The best defense, is a strong offense when dealing with these pests - the sooner the better. Search for head lice when hair is wet.