The chemical composition of fresh hides
and skins falls approximately within the following limits:
Water 60% - 65%
Protein 25% - 30%
Fats 5% - 10%
Note
Tanners
use the terms hide and skin to distinguish
the size of the animal they came from
- hides come from larger animals such
as cattle and skins come from smaller
animals such as sheep, goats and pigs.
The protein
content consists mainly of collagen, and it is this
collagen that is transformed into leather by the tanning process.
Physical structure
The epidermis
is a thin layer of cells that serves as a protective layer
during the life of the animal. It is continually replaced
during growth, the lower layers of cells being the newest
and least stable. The epidermis is removed before tanning,
along with the hair, in a process called liming.
The grain layer, or corium minor, consists of a dense
layer of collagen and elastin protein fibres. The structure
varies according to the animal breed, age, sex and health
and is frequently marked by scratches and the bites of
parasitic insects. The grain layer gives leather its distinctive
appearance.
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to enlarge
The corium major consists of a dense
layer of collagen protein fibres, arranged in larger bundles, and
interwoven to give the structure high strength, elasticity and durability.
The corium major increases in thickness and density with increasing
age, thus calfskins are thinner, smoother and softer than the hides
of mature animals; cow hides are smoother, thinner and softer than
the hides of mature males and bull hides are thick, tough, coarse
grained and very strong.
Thick hides are normally split layerwise through
the corium layer to give a 'grain split', used for grain leather,
and a 'flesh split' mainly used for suede leather. Sometimes an
artificial grain layer is applied to one side of the flesh split
to make it look like grain leather, known as 'finished split', although
the result is not as strong as real grain leather because the corium
lacks the strength of the grain layer.
content consists mainly of collagen, and it is this
collagen that is transformed into leather by the tanning process.)