Leathers are made from different animal skins. Skin from each animal has a distinct character of its own.
The surface of the skin has the markings left by the hair roots (called grain pattern), the structure of which is unique for each animals. Skins of younger animals have finer markings and older animals relatively coarser pores.
Nature of the fiber network which makes up the bulk of the leather also varies from animal to animal. Skins have a top layer (called grain layer) which is relatively compact and contains the hair patterns and the bottom layer (called corium layer) which has a looser fiber network.
Let us briefly look at each animal:
Cattle
This is the most commonly used skin for making leathers (about 65% of leathers produced are from cattle). The markings on the grain surface of cow hides are of uniform size and closely packed together.
Grain layer makes about one fifth of the total thickness of the hide. Cow leathers natural thickness is relatively great. Therefore, they are normally split into two layers during processing. Grain split contains the grain layer and a part of the corium, flesh split is the remaining part of corium.
Cow leathers come in varying sizes and due to their relatively large size, can be used for a variety of products ranging from leather shoes to furniture upholstery.
Buffalo leathers are sometimes used as a cheaper alternative to cow leathers.
Sheep
Sheep skins account for about 20% of leathers used in the world. The grain pattern of the sheep skin is arranged in groups with spaces in between (unlike cow hide where it is uniform thorughout).
The grain layer is almost half of the total thickness. The fiber network is looser and hence weaker compared to cow hides. Also the size of the skins is much smaller compared to cow Therefore, generally sheep leathers can not be used for making footwear (with some exceptions like soft shoes etc) or furniture.
On the other hand it is ideal for making clothing leathers due to its soft and flexible fiber structure.
Sheeps normally have high amount of natural fat. After this fat is removed during processing, voids may be left in the surface resulting in what is called looseness. This is the effect seen as wrinkles on the surface.
Goat or Kid
Goat leather account for about 5% of all leathers produced in the world. Goat skins have two types of hair markings. Larger one are arranged in trios and the smaller ones are arranged around them. This characterestic pattern gives an unique look to the shoes made from goat skins.
The fibers are short and compact (as opposed to sheep skins, where they are short and loose). Therefore, goat skins can also be used for a variety of products ranging from gloves to footwear (and even for upholstery!!). Goat skins produce a finer suede compared to cow hides.
Pig
About 10% of leathers are processed from Pig skins. Pigs do not have many hair, therefore the skin also has relatively fewer markings scattered on the surface. The size of the pores are bigger compared to other animals
As the hair penetrates to the full thickness of the skin, the fiber network contains the holes after the hair is removed during processing. Therefore, even on suede leathers the hair pattern can be seen. The network is compact and small, which gives a fine suede surface.
Pig leathers are also used in variety of products ranging from shoe lining to garments to upholstery.
Others
Leathers from skins of other smaller animals and some fishes are also used for making leather goods.
Leathers with different finishing
Coated finishing
These leathers are finished by application of finish mixes to varying degrees. Depending on the nature and amount coating applied, the leather surface and the defects can be covered up to different extends.
Natural Grain Leathers
This group includes leathers finished with their grain intact. The leathers suitable for finishing of this type should be of good grain quality without deep scars or looseness.
Full Aniline leathers
Full aniline leathers should have no covering material used in the finish coat. The leathers are dyed into a color close to the required color. Two to three coats of transparent finish with or with out dyes is applied. This finish serves as a protection to the grain surface.
Special type of milk protein based binders can be used to finish this type of leathers. These binders can be subjected to high temperature by friction in glazing machine to give a brilliant glossy look to the leather surface.
These types of finishes enhance the natural appearance of the surface and highlight variations present. The quality of raw hide, dyeing and other processing should be of very high standard.
Semi Aniline leathers
Semi aniline leathers are next in the value order. Finish mixes contain relatively small amounts of finer variety of pigments (about 4 to 7 percent in solution) along with dyes. They can be finished using protein binders and glazed or using resin binders which can not be glazed.
The pigments used in the finish can cover up minor scratches and superficial scars. Variations in dyeing can not be covered up.
Imitation Aniline leathers
Imitation aniline effect is obtained by first applying finish coats with high amount of covering material (over 10 to 15 percent in solution) first and then coating with transparent mixes containing dyestuffs.
The bottom coat covers up the defects and variations on the surface, thus the natural grain look is lost to some extent. The top dye coat gives the brilliant aniline dye appearance to the surface.
Pigment Finished leathers
Pigment finished leathers are those types which are finished with relatively high amounts of covering material. Due to cost reasons dyes are not used or used sparingly.
The covering of defects is very good in this finish. However, if the crust is not tight enough it may lead to looseness.
Imitation grain leathers
These types of leathers are made from relatively poor quality hides. The hide surface has a number of deep scars and can not be finished to a uniform look without modifications. Typically, the grain is removed by buffing, special resin binders are used to reduce the looseness of the grain layer and heavy finish coat is applied to get an uniform finished surface.
Corrected grain leathers
The crust is buffed to remove the top grain pattern and treated with a filling type of resin binder, which makes the grain layer tight. Afterwards, several coating of finish mixes with high amount of covering material are applied. Often, an artificial pattern similar to the animal grain (hair-cell prints) is applied using metal plates under heat and pressure (in hydraulic press or roller presses).
The finish can be modified to obtain different end results such as glossy surface, dull surface, waxy surface etc. and the surface is relatively uniform. Leather loses its natural appearance. Special effects such as brush off effect can be obtained by using suitable binders and coloring mixes.
Printed Leathers
These leathers are finished similar to corrected grain leathers, but with a deeper print on the surface. A variety of print patterns such as crocodile print, lizard print etc. can be applied.
Hides of low quality can be used as the surface is entirely replaced with an artificial pattern. Leather strength and natural quality are lost. These leathers are used mainly for making leather goods (wallets, bags, belts etc)
Finished split leathers
Normally, due to the coarse and weak fiber network, split layers can not hold the finish coating well. However, some special techniques can be used to apply finish coatings on the split surface usually with some printed patterns.
These are made from the lowest grade hides, which can not be finished in any other manner.
Buffed and split leathers
Buffed leathers are typically finished to velvet like surface, called nap.
Nubucks
Nubucks are leathers with velvet like surface on the grain layer. Since the fibers in the grain layer are compact and short, the nap is fine and smooth. Depending on the animal the grain pattern will still be visible to some extent.
Nubucks require good quality hides with tight fiber structure and without any deep scars. The cost of making Nubuck is high due to the use of expensive dye stuffs and skilled buffing operations.
Suedes
Sueds are leathers with velvet like surface on the corium layer. Goat skins give a fine shiny nap and cow hides (usually splits) give coarse long nap.
Even hides with very bad grain surface can be used if the corium layer is not affected. Skins with deep scars and inside defects (such as some diseases, flay cuts, vein marks) can not be used.
Oil finishes
Special purpose oils are applied on the surface with or without transparent finish coatings. The oils provide protection as well as unique look to the surface.
Oil Pull ups
Oil Pull ups are made from full grain leathers with application of oil. The oil can migrate when pressure is applied on the surface and come back when the pressure is released. Thus the surface will show tow tone effect when pressed or pulled.
The hide should be of high grade and the dyeing uniform.
Oily Nubuck
Oily Nubucks are finished similar to Oil Pull-Ups on a nubuck surface. The pull up effect may not be as pronounced.
Crazy horse
Crazy horse leathers are made by applying special purpose waxes to a buffed grain surface. These waxes can melt and migrate under frictional heat. As a result when the leather surface is rubbed the color of the rubbed portion changes which does not reverse immediately. This exhibits an antique effect.
Laminated
When the skin or hide is of very low grade a layer of film can be laminated on the buffed grain surface or flesh surface or on the split surface. Depending on the quality of the laminate material and the skill of processing the quality will vary.
The laminated leathers may not withstand the wear conditions in footwear or upholstery and therefore are usually restricted to use in leather goods and low quality shoes.
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