The primary process in leather tanning begins in the Beam House. The rawhides enter soaking drums, the aim being to allow them to re-absorb any water which has been lost after flaying or in the curing process due to salting. This absorbed water re-hydrates any dried inter-fibrillary protein, loosening its cementing effect on the fibres.
The next process is un-hairing and liming. The aim of un-hairing and liming is to remove the hair, epidermis, and to some degree, the inter-fibrillary proteins and to prepare the hides for the removal of loose flesh and fat by mechanical fleshing. When the substrates are plumped in the limed state, it is then split into two or more layers, i.e a grain layer and one or more flesh layers. This is to achieve an even thickness of the substrate.
After splitting, the lime or other alkali in the skin is no longer needed, as it might cause unfavorable effects in the subsequent process. Therefore the substrates are then de-limed. The next process is bating, which involves enzyme treatment to clean inside of the skin and help give softer leather. At this stage the pH of the skin is high and unsuitable for the tanning process. The de-limed and bated skin is then adjusted to a suitable acidity for tannage, known as pickling, and subsequently the skins are tanned. Tanning chemicals converts the protein in the skins into a stable material (Wet-Blue), which will not putrefy and is suitable for a wide variety of purposes. The ultimate difference between rawhide and tanned skin (leather) is that the latter will not putrefy when kept over time.
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