The key word is “tanned.” Like any organic matter, skins and hides will soon begin to decay unless they receive some kind of preservative treatment. They may be simply scraped and sundried—or salted or smoked or soaked in brine or in slaked lime. From some of these processes may come extremely tough and durable products—rawhide, parchment, and vellum are limed—but they are not leather because they have not been tanned.
Taneur This illustration from Diderot’s great eighteenth-century French encyclopedia shows the essential operations in a tannery: A) washing hides in a stream; B) scraping hair or flesh from a hide on the “beam”; C) soaking hides in a series of lime pits; D) bedding hides in a tanning vat with a layer of shredded bark between each hide; E) stirring lighter hides in a hot water tanning solution.
Tanning brings about within the fibrous structure of a pelt certain chemical and physical rearrangements that are still imperfectly understood. Their effect, however, is to render the pelt permanently imputrescible, pliable when dry, and capable of sustaining repeated wetting without hurt. The agents responsible for the transformation, known as “tannins,” are found in almost all plants, in certain minerals, and in various readily oxidizing oils.
TANNING AND CURRYING
The ancient Sumerians, Babylonians, Assyrians, Egyptians, central Asians, and Chinese all knew tanned leather and used it. But who first discovered how to tan it, when that happened, and where, must remain forever unanswered, since the invention of tanning came before the invention of written records. Primitive leatherworkers probably stumbled on different processes at different times and places, and quite possibly a number of widely separated workers discovered the same processes independently.
Until the invention of chrome tanning in the second half of the nineteenth century, little change had taken place in the three basic tanning methods for at least two thousand years. The most widely practiced method involved the use of vegetable tannins. Occidental tanners employed oak bark, gallnuts, and sumac leaves among their chief sources; other plants rich in tannins are found in every continent.
Mineral tanning with alum, called “tawing,” has been in use since earliest time in Babylonia, Egypt, and probably China. Because the leather so made is snow white, workers in this specialty gained the name of “whitetawyers.” Tawed leather, although soft and stretchy, is very strong; quite appropriately, one of his eighteenth-century contemporaries described Richard Bland, the Williamsburg lawyer and political pamphleteer, as “staunch & tough as whitleather.”
Currying—whatever it may have meant to Homer (or to Alexander Pope)—is not a method of preparing hides and skins from fresh-slaughtered animals, but a complex of processes for treating leather already tanned. These processes include smoothing the leather, paring it down to even thickness overall, especially working fatty matter into it for pliancy and water resistance, and giving it whatever surface dressing, color, and finish its intended use calls for. Prominent among such uses in the eighteenth century were shoe uppers, harness and saddlery, upholstery, trunkmaking, and bookbinding.
