Before he laid down even a dot of paint, Vermeer would have weighed, ground, burned, sifted, heated, cooled, kneaded, washed, filtered, dried and oiled his colours. Some pigments – the rare ultramarine blue made from lapis lazuli from Afghanistan, for example – had to be plunged into cold vinegar. Others – such as lead white – needed to be kept in a hut filled with horse manure. The fumes caused the lead to corrode, creating flakes of white carbonate that were scraped off by hand.
Vermeer knew how to soak old leather gloves to extract ‘gluesize’, applied as a coating to artists’ canvas. Or he might have followed the recipe for goat glue in Cennino Cennini’s painters’ manual The Craftsman’s Handbook: boiled clippings of goat muzzles, feet, sinews and skin. This was best made in January or March, in ‘great cold or high winds’, to disperse the goaty smell.
An artist had to be a chemist – and he had to have a strong stomach. He would have known, writes Jelley, ‘the useful qualities of wine, ash, urine, and saliva’. ‘Do not lick your brush or spatter your mouth with paint,’ warned Cennini. Lead white and arsenic yellow were poisonous, goat glue merely unpleasant.
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