After soaking, the hides and skins are taken for the next operation where these are treated with milk of lime with or without the addition of sharpening agents like sulfide, cyanides, amines etc. The objective of this operation is to; remove the hairs, nails and other keratinous matters. Remove some of the interfibrillary soluble proteins like mucins. Swell and split up the fibers to the desired extent. Remove some of the natural grease, fats and oils. Bring the collagen to a proper condition for satisfactory tannage.

The weakening of hair is dependent on the break down of the disulfide link of the amino acid called cystine, which is the characteristic of the keratin class of protein like hair and wools. The hydrogen atoms supplied by the sharpening agent reduce the cystine molecule to cystine and the covalent links are ruptured. Some of the “unhairing agents” used during liming are; Sodium Sulphide, Sodium Hydroxide,  Sodium Hydrosulfite,  Arsenic Sulphide,  Calcium Hydrosulfide,  Dimethyl Amine and Sodium Sulphydrate. The majority of hair is then removed using a machine, with remaining hair being removed by hand using a dull knife, a process known as scudding.

Depending on the end use of the leather, hides may be treated with enzymes to soften them in a process called "bating". But before bating, the pH of the collagen is brought down to a lower level so that enzymes might act on it. This process is known as "Deliming". Once bating is complete, the hides and skins are treated with a mixture of common salt and Sulphuric acid in case a mineral tanning to be done. This is done to bring down the pH of collagen to a very low level so as to facilitate the penetration of mineral tanning agent into the substance. This process is known as "Pickling". The common salt penetrates the substance twice as fast as the acid and checks the ill effect of sudden drop of pH.

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