Liming

Abstract

To allow chemicals to penetrate down the hierarchy of structure of the collagen within hide and leather, it is necessary to split the fibres at the fibril bundle level, so-called ‘opening up’, a form of selective damage. Typically, this is achieved by treating with calcium hydroxide for several hours, during which period the dominant reaction is hydrolysis, of the collagen at the peptide links and sidechains, of the non-structural proteins, of glycosaminoglycans and of cutaneous fat. Whether or not lime is involved in the opening-up step, it is usually called ‘liming’. There are variations in liming technology; modern versions often employ proteolytic enzymes. In these circumstances, hydrolysis is targeted at the protein, so a change in the isoelectric point does not occur. Outside the drum, the limed hide is vulnerable to a fault called ‘limeblast’, which is caused by a reaction between solid lime within the grain surface and carbon dioxide in the air; the resulting solid calcium carbonate disrupts the surface, leading to a dull appearance.