Sialkot, Pakistan (PressExposure) September 08, 2009 -- Leather is an incredibly wonderful natural fabric that's been used for thousands of years. No man made material has been able to surpass the natural beauty and toughness of leather but there are defects which may be caused during the life or after death of an animal.
Imperfections in the grain surface or structure of a hide or skin resulting in unsightly appearance and/ or weakness of the resultant leather. Such defects may have arisen during the life of the animal, or may have developed in the flaying and/or preparation of the stock. Defects exist on natural leather surfaces and they usually cannot be eliminated during processing. No international criterion specifies the compensatory counting for calf leather surface defects. So complicated negotiation causes additional cost and argument between suppliers and purchasers
Defects caused to hides during the life of an animal
Defects caused during life include:
1) Scars, resulting from scratches or cuts. (When the cut is healing, the fibers grow densely packed together, and the healed skin is often hard, raised, and lacking hair follicles. Scar damage is also caused by branding the animal for ownership purposes, usually in the butt area, which is the best part of the hide)
2) Infestations, such as ticks, warble flies, and mange. (Ticks pierce the skin to suck blood, leaving holes that look either like pin pricks or minor scars in the grain of the leather. This defect occurs mainly in the belly areas of the skin. Sarcoptic mange mites enter the epidermis and tunnel around, causing the cells to multiply and the hair to fall out. The grain surface becomes roughened, and the animal generally compounds the damage by rubbing to relieve the itching. In demodectic, or follicular, mange, the mites penetrate into the dermis itself, where a wall of fibers is formed to surround and "encyst" them. The cysts generally are seen on the grain of unhaired skins as small swollen nodules. Tanning and drying processes shrink the contents of the cysts, causing the grain surface to sink over the cavity so that the defects are seen as shallow depressions, though the grain surface itself is not generally damaged;
3) Infections. (If ringworm, which is a fungus, heals it leaves no scars, but if the animal is slaughtered while still infected, the grain appears coarse at the site of the infection);
4) cockle, which occurs in wooled sheep immediately before shearing. (This defect appears as boil-like hard spots, of varying size, which occur in rows at right angles to the spine from the shoulder to the butt, and, while the defect disappears rapidly after shearing, it cannot be eliminated during manufacture of the leather.)
Defects caused after the death of an animal
Damages caused after death include:
1) flay cuts and gouges, which cut into the fibers of the dermis. (In thin leathers they show through and thereby spoil the grain. Some flay cuts go completely through the hide or skin, ruining it completely. These kinds of cuts are usually the result of careless or improper flaying);
2) putrefaction, which is the result of bacterial growth which starts almost immediately once the animal is dead, unless the skin is properly cured, especially on the exposed flesh side. : PUTREFACTIVE DAMAGE;
3) vainness, in which branching lines of blood vessels can be seen on the flesh side. (If, because of poor curing or old age, for example, the structure around them becomes loose, the skin is said to be veiny, and the branching pattern of the veins usually shows through on the grain side. Veininess can actually at times be attractive in some skins, such as VELLUM.
4) damage from heat, which may occur on hides and skins in tropical areas. (It is a common fault with ground-dried skins. Sun Damage that occurs to a hide or skin when it becomes heated above a certain critical temperature while it is still moist and is laid out in the sun to dry (cure). A completely dry skin can become very hot and still not be affected under normal conditions of cure, but prior to this a skin is very susceptible to damage.
Also, the drying of a salted skin proceeds so uniformly throughout its entire thickness that the cooling effect produced by evaporation off its surfaces maintains the temperature of the entire skin below the danger point until it is uniformly dry. Without salt, however, a skin tends to dry unevenly when laid out in the usual manner, which is flesh side up. This can happen because the flesh side can dry out completely and begin generating heat, while the underside remains moist, and, being shielded from evaporation, also begins to generate heat. This is especially the case when pieces of flesh, generally of a fatty nature, are present on the flesh side, and further retard the drying of areas beneath them.