Graphic Arts holds books with many types of bindings, including books bound in the skin of cows, pigs, sheep, and other mammals. Recently, we acquired a book described as bound in cat’s paw calf. A quick search revealed several other volumes in the stacks with similar cat’s paw bindings.
Happily, it turns out that “cat’s paw” is a descriptive term for the leather made from young cows not cats. This is a variation of Tree calf or Tree marbled calf. For such bindings, a light-colored calfskin has been treated with chemicals to represent a mottled tree trunk with branches or the marks made by a cat’s paw.
The leather is first paste-washed and the book hung between two rods, which keep the covers flat. The book is tilted so that it inclines upward towards it head. A small amount of water is applied to the center of both covers to form the trunk, then more water is thrown on the covers so that it runs down to the trunk and to a central point at the lower edge. Copperas (a green hydrated ferrous sulfate) is sprinkled in fine drops on the covers, followed by potassium carbonate, which causes the chemical reaction that etches the leather to form a permanent pattern in shades of gray.
This and other binding descriptions can be found in Etherington & Roberts’ Bookbinding and the Conservation of Books: A Dictionary of Descriptive Terminology available now online: http://cool-palimpsest.stanford.edu/don/dt/dt3574.html or on paper: Graphic Arts GA Oversize Z266.7 .R62q