Leather Production Processes - Crusting

Crusting

Crusting is when the hide/skin is thinned, retanned and lubricated. Often a coloring operation is included in the crusting sub-process. The chemicals added during crusting have to be fixed in place. The culmination of the crusting sub-process is the drying and softening operations. Crusting may include the following operations:

• wetting back - semi-processed leather is rehydrated.
• sammying - 45-55%(m/m) water is squeezed out the leather.
• splitting - the leather is split into one or more horizontal layers.
• shaving - the leather is thinned using a machine which cuts leather fibres off.
• neutralisation - the pH of the leather is adjusted to a value between 4.5 and 6.5.
• retanning - additional tanning agents are added to impart properties.
• dyeing - the leather is coloured.
• fatliquoring - fats/oils and waxes are fixed to the leather fibres.
• filling - heavy/dense chemicals that make the leather harder and heavier are added.
• stuffing - fats/oils and waxes are added between the fibres.
• stripping - superficially fixed tannins are removed.
• whitening - the colour of the leather is lightened.
• fixation - all unbound chemicals are chemically bonded/trapped or removed from the leather
• setting - area, grain flatness are imparted and excess water removed.
• drying - the leather is dried to various moisture levels (commonly 14-25%).
• conditioning - water is added to the leather to a level of 18-28%.
• softening - physical softening of the leather by separating the leather fibres.
• buffing - abrasion of the surfaces of the leather to reduce nap or grain defects.