The properties of leather vary considerably depending upon the type and quality of both the skins and the tanning process. Every piece of leather has individual markings which relate to its origins and add character to each skin.
Like a fine wine, a good quality leather garment should improve with age. The natural elasticity of each hide means it is flexible and will stretch and return to its original shape. Leather also has a natural tendency to repel liquids and resist staining. It's also fire resistant, and emits no toxic fumes, even when exposed to intense heat.
Relative to virtually all man-made textiles, leather is very strong and has a high resistance level to tears and punctures. The comfort provided by most leather goods is due in part to leather's ability to combine breathing and insulating properties. You may have heard... "Leather is hot in summer and cold in winter." In reality, leather adjusts constantly to its environment. Because it is a natural product, leather "breathes" freely, maintaining a comfort level in all seasons.
Types of Garment Leather
Cowhide is the most common leather used in the making of garments, furniture and leathergoods. Cowhide as a category covers a wide spectrum of textures and quality, but generally, it is quite durable, easy to care for and resistant to water and dirt. Cowhide leather will maintain its integrity, taking on the shape of the wearer, making it more comfortable with everyday use. This affordable, functional leather offers fashion, value and endless colours and style.
Lambskin is a very soft, luxurious leather. Its natural lightweight layers give it a distinctive, velvety touch, which suites form fitting jackets, pants, skirts as well as coats. But don't let its delicate texture discourage you. With a little extra care, lambskin is very wearable and the ultimate luxury.
Pigskin is by far the most popular and versatile, easily transformed into fashion's most current looks. When tanned on the outside, it produces smooth napa finish, often used for jackets and accessories. Tanning on the inside results in a silky suede finish. The natural, lightweight structure of pigskin produces delicate patterns, textures and silky soft naps, perfect for sportswear, shirts and blazers.
Sheepskin refers to the hide of a sheep used with the wool still attached. Usually, the wool side faces into the garment or accessory, but it can also be made reversible. The wool can be ironed, which means straightened to yield a smooth, fur-like appearance, or it can be left naturally curly. Whichever way the wool is styled, this is the warmest leather available.
Shearling is quite similar in appearance to sheepskin, the term shearling refers to hides from lambs which are generally much lighter in weight then sheepskin hides and much softer. Although they may be lighter, shearling coats are just as warm as the heavier sheepskin. They are an elegant alternative to a fur coat.
Glossary of Leather Terms
Aniline Leather that is tumbled in vats so the dye is completely absorbed by the skin. There is no other colouring agents or process, thus the finished leather tends to look and feel more "natural" - the unique markings and character of each skin are apparent. By way of analogy, this treatment is akin to the "staining" of wood. Usually, the best quality hides are reserved for this process, as aniline leathers are valued highest by consumers.
Antiqued The light application of one colour over another (usually a darker color over a lighter one), to create highlights.
Corrected Grain Leather Leather whose natural surface texture has been altered.
Drum-dyed A dyeing process in which leather is immersed in dye and tumbled in a rotating drum, allowing maximum dye penetration.
Dyeing The application of colour, either by spraying, hand rubbing or immersion.
Embossing A process in which design is added to leather by pressure to alter or correct the surface resulting in uniform imitation grain.
Finishing Any post tanning treatment, such as: dyeing, rolling, pressing, spraying, lacquering, antiquing, waxing, buffing, embossing, glazing, waterproofing, or flame proofing.
Grain The distinctive pore and wrinkle pattern of a hide; may be either natural or embossed.
Hand A term used to describe the softness or feel of leather.
Hides Skin of large animals, usually cattle.
Leather A generic term for all hides and skins which have been tanned and finished.
Napa A term used for leatherized sheepskins.
Nubuc Aniline leathers on which the surface has been brushed to create a texture similar to that of velvet. It is often mistaken for suede, but suede is the flesh side of a piece of leather while Nubuc is an effect that is done to the grain side, making it considerably stronger.
Patina A luster that develops with time and use.
Pigmented Leather that has been sprayed with a surface colour in addition or instead of the dye process and is analogous to the "painting" of wood. While generally less appealing to the touch than aniline leather, pigmented skins are required for applications such as motorcycle leathers where durability is the key consideration.
Premium select A term describing hides with a minimal amount of scars or blemishes, usually less than 5% of all hides.
Sanding Refers to the removal of scars and blemishes from a hide by buffing.
Semi-Aniline Leathers which are a combination of both pigmented and aniline dyed; a very light pigment is added to even out the colour and increase the durability. Most garments are made with semi-aniline leathers.
Splits Underlying layers of leather usually used for suedes.
Suede Suede is the underneath portion of a hide after the splitting process. Compared to the durable top grain, this layer of the hide is much thinner and there for most commonly used for garments and small leathergoods - and not for furniture.
Tanning Treating raw hides to become nonperishable.
Tumbling A process in which hides are tumbled in a rotating drum to soften the hand or enhance the grain. Hides selected for furniture are sliced to a uniform thickness on precision machines. Only the outer surface (top grain) is used. The lower portions or splits are weaker, due to the elongated cell structure. Splits are subject to stretching and therefore provide an unstable base, which results in cracking of the finishes.
HOW LEATHER IS MADE
The tanning industry is a multi-billion dollar industry with factories throughout the world. While leather has always been largely a byproduct of the meat industry, today this is a universal fact; the most notable exceptions being some types of snake skins. The greatest and most valuable advancements in tanning technology relate to the mitigation of its environmental effects. Today, the vast majority of countries with tanning industries have stringent environmental regulations to ensure that these technological advancements are, in fact, employed. While the exact specifications and procedures for tanning vary considerably, depending on the type of skin and its application, the basic processes are common to all tanning operations.
The Tanning Process
The skins and hides are received at the tannery in a cured form, which means they have been treated with salt to prevent rot before they leave the meat packing plant. The hides are then soaked in water to soften them and to remove the remaining salt solution. The soaking period varies from two to forty eight hours. The next step is fleshing. Machines equipped with a rubber roller and a shaft to which spiral knives are attached remove the flesh and tissues from the inner side of the skin. These knives leave a clean, uniform surface. After fleshing, workers transfer the skin to a department of the tannery known as the beam house. Here the hair is removed by soaking the hides in a vat with a solution of lime and sodium sulfate. The hides are milled or kept in motion in the vat for several days.
The next operation involves removing the lime from the skins. After washing with cold water they are placed in a bating vat which contains an enzyme and a sulfate or chloride. Bating also softens the texture of the hide during this 3 to 4 hour treatments. At this stage, the hides enter one of two possible processes of tanning: Vegetable or Chrome tanning. Leathers for shoe soles, heavy cases, harnesses and most upholstery applications are prepared by vegetable tanning. Many plants and barks contain a bitter ingredient called tannin. It has the property of combining with proteins to form a compound that will not rot or decompose easily. In this case, the protein is the hide and after tannin is added, the compound is leather. The principal sources of tannin are leaves, nuts, bark and woods of hemlock, oak, chestnuts and various other types of trees.
Chrome tanning is used for tanning the upper leather of shoes, handbags, wallets and garments. Prior to chrome tanning, the hides must be pickled after the bating step. Pickling involves soaking the hides in a solution of salt and acid for several hours to achieve a low pH level. This is necessary because the chrome-tanning agents that are to follow are not soluble otherwise. The pickled skins or hides are then placed in a tanning drum containing a solution of common salt, soda and acid. The chemical reaction to the compounds tans the hide and after 5-10 hours, the conversion to leather has been effected.
Dyeing & Finishing
After the leather has been tanned, it is then split and shaved to a uniform thickness appropriate for the intended product. Dyeing or colouring is achieved by placing the leather in another drum with a combination of colouring materials and chemicals to increase their penetration. This process may take several hours.
Fat liquoring is the last step in the "wet" stage and requires about one hour. Here the leather is placed in a drum with a variety of oils and greases. This step and the combinations of oils employed, determine the pliability of the leather. The leather is then dried to remove all excess moisture. A number of different methods are used, each having a different "dehydration" level which influences the characteristics of the final product. Often the leather is then buffed. All skins have natural healed scratches or blemishes, which attest to the genuineness of leather. However, to improve its final appearance, it is often desirable to lightly sand or buff the grain surface. If the leather is not buffed, the leather is top or full grain leather.
Finishing involves the application of film-forming materials to provide abrasion and stain resistance and to enhance colour. Pigments are also added when a more opaque or vivid colouring effect is required. However, with smooth or top grain leather, usually only a light, transparent coating is applied. This is known as aniline dyeing. Of the two, aniline finished leathers are the finest quality. The final processing step to influence the appearance and feel of the leather is called plating. The plating operation is done on a press capable of exerting up to 300 tons per square inch. The plating smoothes the surface of the coating materials just applied and firmly affixes them into the grain. At the same time, the plate may be specially engraved to emboss a particular pattern on the leather.
The specifications and required characteristics of the tanned leather is determined by the end use of product for which it is intended. Tanneries produce to order for a wide variety of final goods manufactures; there is a huge range in the quality of both materials and workmanship in leather goods. In 1995, total world leather production was approximately 7,000,000 metric tons of cowhide; 1,400,000 metric tons of lambskin, shearling, sheepskin; 800,000 metric tons of pigskin and 450,000 metric tons of goatskins. It has been estimated that more than 2,000,000 people in the world are employed in the various branches of the leather industry.
Today, the leather tanning industry stands out as perhaps the most productive byproduct industry in the world. It is hard to imagine the environmental impact of the additional synthetic product manufacturing which would be required to replace all of the current applications for leather, suede and shearling. It is impossible to imagine how any of these synthetic substitutes could ever match the esthetic appeal of genuine leather.
