Making Leather - Liming
The skins are put into a lime solution to remove any hair by removal of the keratin that is present in the hair, scales and in the epidermis of the skin is hydrolyzed in the presence of alkali (at pH values greater than 11.5). The disulfide bridges found in keratin protein are cleaved but can be reformed. Long periods of liming will result in hair removal. The main removal of keratin is performed using the un-hairing operation. In traditional processing liming/unhairing was indivisible and took place at the same time. Modern liming methods, and in particular, the processing of sheepskins the hair is removed first and then limed in a liming drum. In hair-save technology, the hides are un-haired first and then limed for a further 12-18 hours.
The action of liming, in particular the swelling of the skin, results in the splitting of the fibre bundle sheath. This allows increased access to the fibres which allows better tanning.