Lime white
Not really a pigment so much as the wall itself, used as a colour. Lime white is slaked lime — the same material as the plaster — and in true fresco it is both the ground, the binder and the lightest value available.
Origin
Limestone burnt in a kiln gives quicklime; quicklime slaked with water gives calcium hydroxide, a white paste that was traditionally aged in a pit for months or years, the best Italian workshops keeping it for a decade or more. Painters called the aged product bianco San Giovanni when it had been dried into cakes, air-cured so that the surface converted to calcium carbonate. Cennini gives the recipe: slake the lime, wash it repeatedly, shape it into small loaves and dry them in the sun.
In art history
Lime white is inseparable from fresco, and therefore from the largest paintings in European art. Every highlight in the Arena Chapel, the Brancacci Chapel and the Sistine ceiling is either bare plaster left unpainted or lime white brushed on. It is also the white of Roman wall painting at Pompeii, of Byzantine and Romanesque church decoration, and of the whitewashed architecture of the Mediterranean generally. In this atlas it appears in the fresco-based eras, where it does a job no other white could do: lead white and azurite are attacked by the alkaline plaster, but lime white is the plaster.
In the studio
In buon fresco the painter works on wet lime plaster, and as the wall dries the lime absorbs carbon dioxide from the air and reverts to calcium carbonate, locking the pigment particles into a crystalline skin. Nothing else is needed — there is no binder in fresco, and this is why fresco lasts. The constraint is time: a section of plaster stays workable for a day, the giornata, and the artist must finish that patch before it sets, which is why fresco surfaces show visible seams and why nothing can be reworked. Lime white brightens as the wall carbonates, so a fresco looks different when dry from when painted, and a fresco painter has to anticipate a colour they cannot yet see.
Afterlife
It never disappeared — lime wash and lime plaster are still standard in conservation and in traditional building, and have returned to fashion in architecture for their vapour permeability and their particular chalky depth. As an artists' pigment it belongs to fresco, and fresco is now practised by a small number of specialists, mostly in restoration.
Where it appears
Every era and artist in this atlas whose palette includes this pigment.