Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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tree calf ( tree marble )

A form of cover decoration consisting of a smooth, light-colored calfskin treated with chemicals in such a manner as to represent a tree trunk with branches. In the usual manner, a dual design appears on upper and lower covers. The leather is first paste-washed, and the book is then hung between two rods which keep the covers flat. The book is tilted so that it inclines upward towards its head. In order to bend the boards outwards, i.e., warp slightly to a concave shape, so that the solutions will run properly, the insides of the hoards are not filled in until the decoration is done. 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 of the hoards. Copperas (a green hydrated ferrous sulfate) is then sprinkled in fine drops on the covers, followed by potassium carbonate (salts of tartar). which causes the chemical reaction that etches the leather to form a permanent pattern in shades of gray, ranging from faint to very dark. Calfskin was used for this decoration in preference to sheepskin (although 19th century examples of sheepskin tree do exist) because in addition to being a much superior leather, it takes a better polish, which suits this style of decoration admirably.

The spine of the book is protected during the marbling so that it will not be touched by the water or chemicals. The entire process calls for considerable experience and dexterity of execution, because if the result is to be effective the copperas and potassium carbonate must be applied in the correct amounts, as well as in the proper manner, while the initial water is still running down the covers; otherwise the effect will be little more than sprinkling.

Late in the 19th century attempts were made to produce the tree calf effect with the use of an engraved block, which was used to print a design on the covers in black, but the results were ineffective because the block did not provide the shading which the genuine method achieved. The popularity of tree calf began to decline before the First World War, and by the late 1920s this once very popular form of decoration had virtually passed from existence. The first known tree calf decoration dates from about 1775. See: PLATE V . (83 , 94 , 236 , 264 )

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