Acids which have penetrated into the leather during tanning are removed during the neutralising stage. Alkaline sodium carbonate is used in a concentration of 1.2%. Neutralising is necessary, to allow fat-liquoring. There are no attempts to bring the pH value of leather to 7 during this stage, since this would dissolve the binding of the tannins to the skin-fibres and thus drastically reduce the durability of the leather. In practice, a pH value of 4-6 is desired.
Video about the leather production
|Process steps in the leather production|
|Storage - soaking - liming - fleshing - splitting - pickling - tanning - neutralising - withering - sorting - shaving - dyeing (through colouring) and fatliquoring - drying - finish - softening - final check|
|Chrome tanning - Vegetable-tanned leather - Synthetic tanning - Tanning with fats and oils|