Hides are normally split into two layers. This creates a uniform thickness. The top layer is used for upholstery. The bottom layer is of non-uniform thickness and processed for different uses.
Adjustments in the acid/alkali balance (pH) of the hide are made before applying the chrome tanning salts. These operations are called Deliming and Pickling.
The chrome tanning salts react chemically with the molecules, making the fibre network resistant to bacteria. Modification of the final characteristics are made as required for the final leather product.
Modification of the leather
The main characteristics of the modified leather are:
· Leather Thickness
· Colour
· Softness
A number of other characters can be changed depending on the type of the leather being made by using specific chemicals.
After adjusting the pH balance, further chemical treatments are carried out.
Retanning uses special materials to change a range of characteristics. Dyes colour the fibres of the leather and oils are used in fatliquoring to soften the leather. Waterproofing, flame proofing, solvent resistance etc. can be applied at this stage.
The leathers are stretched and flattened in Setting Machines and then dried. The dried leather undergoes a number of mechanical processes to make it soft, flat and tight.
Surface finishing
A variety of finishing operations is carried out on the leather. Coating with coloured mixes is the most commonly used.