White bronzing on plaster
One must apply four layers of painters’ distemper glue onto the plaster portrait, leaving one layer to dry at a time. Then apply gently some burnt English point ground on a marble slab, or some lead burnt, ground and distempered with a bit of gum or glue. When dry, rub gently with a little cotton and the plaster portrait will look like lead. Others grind minium with quicksilver.