Liming is a process used for

parchment Parchment is a writing material made from specially prepared untanned skins of animals—primarily sheep, calves, and goats. It has been used as a writing medium for over two millennia. Vellum is a finer quality parchment made from the skins o ...

leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hog ...

processing, in which hides are soaked in an alkali

solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Soluti ...

. It is performed using a drum and paddle or a pit. Its objectives are: * Removal of interfibrillary proteins. * Removal of

Keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

proteins. * Collagen swelling due to the alkaline pH. * Collagen fibre bundle splitting. * Removal of natural grease and fatsS.S. Dutta, ''An Introduction to the Principles of Leather Manufacture'', p. 160 Liming operations of cattle hides usually last 18 hours and are generally associated with the alkaline phase of

beamhouse operations Tanning is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed. Tanning hide into leather involves a process which permanently alters the protein structure of skin, makin ...

Removal of interfibrillary proteins

The interfibrillary proteins are denatured by the presence of alkali (particularly sodium sulfide), rendered soluble, facilitating their removal from the leather. Removal is done by the mechanical action of liming or reliming, but more prominently when the pelt is deswelled (during deliming). Failure to remove these proteins results in a hard, tinny leather (due to fibre glueing upon drying) that is brittle and inflexible.

Keratin removal

that is present in the hair, scales and in the epidermis of the skin is hydrolyzed in the presence of alkali (at pH values greater than 11.5). The

disulfide In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

bridges found in keratin protein are cleaved but can be reformed. Long periods of liming will result in hair removal. The main removal of keratin is performed during the unhairing operation. In traditional processing, liming and unhairing were indivisible and took place at the same time. During modern liming methods, and in particular the processing of

sheepskin Sheepskin is the hide of a sheep, sometimes also called lambskin. Unlike common leather, sheepskin is tanned with the fleece intact, as in a pelt.Delbridge, Arthur, "The Macquarie Dictionary", 2nd ed., Macquarie Library, North Ryde, 1991 Uses ...

s, the hair is removed first and then limed in a liming drum. In hair-save technology, the hides are unhaired first and then limed for a further 12–18 hours.

Alkaline collagen swelling

The presence of calcium hydroxide results in the alkaline swelling of skin. The result is an influx of water into the hide/skin, and a marked increase in fibre diameter and fibre shortening. The thickness of the skin increases, but the surface area of the pelt decreases. The weight increase, owing to the uptake of water, results in a doubling of the hide/skin weight. However, this weight also needs to take into consideration that proteins (especially the hair) have been removed, and the fleshing operation is often performed after liming.

Collagen fibre bundle splitting

The action of liming, in particular the swelling of the skin, results in the splitting of the fibre bundle sheath. Owing to the fibre diameter increasing, the bundle sheath cannot contain the thicker fibres, and it bursts open. This allows increased access to the fibres, which allows better

tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

, retanning,

dyeing Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular c ...

and fatliquoring.

References

{{leather Leathermaking