Bedford style
Hand-stained bindings produced from a leather
sometimes referred to as "fair calf" (a bark
tanned calfskin), washed over frequently with a
weak solution of potassium carbonate (K
2 CO 3 ), and exposed to
light. The staining process took as long as 6
months. In addition to the potassium carbonate,
copperas (ferrous sulfate—FeSO 4
), also known as "green vitroil," was used to
produce a particular effect. The carbonate gave a
warm brown-toned sprinkle, the sulfate gave a
gray, and the two together gave a black. Cf: ETRUSCAN CALF . (94 , 154 , 236 , 347 )