106 Chapter 5
The pelts were then given a further cleansing and opening up treatment
using the alkaline bating, puering or mastering process or the acidic raising
or drenching process. In the alkaline processes, the pelts were immersed in a
warm infusion of bird droppings or dog dung. This removed excess lime and
biochemically altered the hide structure to give a softer leather with a finer,
more flexible grain. In the first decade of the twentieth century the active
ingredients in the dung were found to be proteolytic enzymes secreted in the
pancreas and activated by ammonium salts. The acidic raising or drenching
process involved treating the hides in liquors prepared by fermenting barley,
rye and other vegetable matter. The action of the fermentation was to produce
a complex mixture of organic acids and enzymes which broke down the non-
fibrous proteins of the skin and removed excess lime. Once the pelts were
judged to be in the correct condition, the hides were again washed and worked
over the beam with a blunt knife to remove the slime that had been liberated.
These pre-tanning processes could have taken up to three months.
The preliminary stage of the tanning operation itself was to immerse the
hides in weak, almost spent, tanning liquors, moving them around continu-
ously. Once the colour of the grain was judged to be satisfactory, the hides
were transferred to a further set of pits. To prepare these, a layer of ground
vegetable-tanning material was tipped into the bottom of the pit and a hide
laid flat over it. The vegetable-tanning material employed depended on what
was available locally. Birch, willow, spruce and larch were used in Northern
Europe and Russia; various species of oak in Britain and Central Europe; sumac,
valonia, oak galls and various acacias around the Eastern Mediterranean.
A layer of ground tanning material was strewn over the hide, then a second
hide spread out over it. In this manner alternate layers of tanning material and
hides were added until the pit was nearly full. A final layer of tanning mater-
ial was piled on top and the whole pit filled either with water, or an infusion
prepared by extracting tanning materials with cold water. The hides were
generally kept in these pits for at least a year, and the whole layering process
could be repeated up to three times. When the tanner had judged the hides to
be fully tanned, they were rinsed off and smoothed out. The leather was then
dried out slowly in a dark shed, fitted with louvered panels to control the rate
of drying.
The dried rough leather was sold to a currier whose first operation was to
dampen the skin and soften it. This was followed by a scouring operation in
which the leather surfaces were scrubbed clean. The skins were then pared
down to the required thickness after which they were worked on a bench to
remove loose tanning materials, flatten and stretch them. They were then
partially dried and impregnated with a warm mixture of tallow and fish oils.
If a soft, fine product was required, further mechanical operations were
undertaken. These had the effect of separating the tanned fibres and allowing