To remove the surface dirt, tiny swabs of cotton wool were rolled onto a wooden stick. The swabs were dampened with saliva and gently rolled across the surface of the painting. Much care had to be taken to not over-wet the swabs or to rub the paint, as the oil paint film was relatively young (only 30 years old) and therefore still soft and vulnerable to abrasion. Due to the thickness of the paint layer and the lengthy period of time required by oil paint to harden, it would be possible to accidentally remove traces of pigment.
The oily staining was reduced mechanically using a scalpel and, where possible, chemically using an organic solvent on a small cotton swab.