Crust leather is the term applied to leather, which is dried after tanning but has not yet been dyed. In the case of chrome-tanned leather, this is known as "chrome crust" and, for vegetable-tanned leather, as "vegetable crust". In some definitions of crust, the leather is described as having been dyed through but not finished.
Vegetable tanned crust leather processed.
Unusual: Chrome crust processed. The colouration with chromium only is unattractive and therefore a cheap solution.
Crusting may include the following working steps depending on the type of leather:
- Splitting: The leather is split into one or more horizontal layers.
- neutralisation: The pH of the leather is adjusted.
- Retanning: Additional tanning imparts properties.
- Dying: The leather is coloured in the drum.
- Fixation: Unbound chemicals are chemically bonded or removed from the fibres.
- Whitening: The colour of the leather is lightened.
- Fatliquoring and Stuffing: Fats, oils and waxes are added between the fibres to soften the leather.
- Shaving: The leather is thinned using a machine which cuts leather fibres from the flesh side.
- Wetting and Conditioning: Leather has to be rehydrated depending on the following working steps.
- Sammying: Water is squeezed out the leather.
- Drying: The leather is dried to different moisture levels.
- Filling: Dense chemicals are added to make the leather harder and heavier.
- Stripping: Superficially fixed tannins are removed.
- Softening: Physical softening of the leather by tumbling and stacking.
- Buffing: Abrasion of the surfaces of the leather to reduce nap or grain defects.