Leather 105
leather, as well as for other purposes, long before the pre-dynastic Egyptian
period.
It has been suggested that vegetable tanning developed from a desire to
colour oil or alum-processed skins. Interestingly the earliest surviving recipes
for the preparation of leather, dating from Babylonian times about 3000 years
ago, show that a combination of these three processes were employed:
You will steep the skin of a young goat with the milk of a yellow
goat and with flour. You will anoint it with pure oil, ordinary oil
and the fat of a pure cow. You will soak the alum of the land of the
Hittites in grape juice and then cover the surface of the skin with
gall nuts collected by the tree growers of the land of the Hittites.Certainly by the classical Greco-Roman period, vegetable tannage had
developed into an important craft-based industry and little fundamental
change appears to have occurred until the beginning of the nineteenth century.
The great majority of leather artefacts surviving in museums, historic
houses and private collections will have been vegetable tanned. This, there-
fore, is the predominant material that conservators will be required to deal
with. The method of manufacture of this product will therefore be considered
first. Significant changes were made during the late nineteenth and early
twentieth centuries in the processes employed to make vegetable-tanned
leathers. Some of these have had serious consequences regarding the rate of
deterioration and it is this class of leather which most frequently requires con-
servation treatment today. These changes will therefore be discussed separately.
3.1 Vegetable Tanning Processes
Medieval and Pre-Modern Period. The first job of the tanner was to wash
the hides free from blood and dung. This was often done by immersion in the
local stream. It was then necessary to loosen the hair to enable it to be scraped
off without damaging the grain surface. The most primitive method was to
pile the hides until putrefaction set in just enough to loosen the hair roots. An
alternative method was to soak the skins in alkaline liquors prepared from
wood ash or, more commonly, lime. A third method can be considered as a
combination of the first two. In this, the hides were immersed in lime liquors
which had been “mellowed” by repeated use. These liquors would have con-
tained large concentrations of organic breakdown products which would have
accelerated the depilatory action. The hide was then spread over a wooden
beam and both sides scraped with tanners’ two-handled knives. The hair side
was scraped with a blunt, unhairing knife and the flesh with a sharper, two-
edged, fleshing knife.