Understanding Leather

Why are some leathers more valued than others? Leathers have a distinct individuality, not only in appearance, but also in feel. From the most luxurious and costly to the more economical, how these differences are achieved, and what makes one more desirable or more expensive that another are explained below.
The Ideal Upholstery Medium: Not all beef animals produce hides suitable for leather upholstery: this is determined by the type of animal and its place of origin. Tanners buy hides in bulk, sight unseen, with all qualities included. When graded, only three-to-five percent of the hides can be used without having to alter, or “correct” the surface before coloring. These are the premium leathers. The remaining hides have their surfaces corrected by either sanding, embossing, pigment coloring, or a combination of these. The more correction required, the less expensive, supple and natural the leather will be.

Leather is the strongest sheet material known to man. Its tough physical structure comes from an intricate network of natural animal fibers. Its strength makes leather virtually impossible to tear or puncture. It will not readily burn or melt, as will most fabrics and vinyls.

Leather adjusts constantly to it environment. It will not become hot and stick in the summer or cold and harsh in the winter, as imitations will. Because it is a natural product, genuine leather will breathe and ventilate, wicking away body heat. Leather mellows gracefully with age and regular use, and its patina is enhanced even by the natural oils from our hands.

Assessing the Quality-Cost Relationship of Leather Upholstered Furniture: The most difficult and confusing aspect of purchasing leather upholstered furniture is the assessment of its quality. “Leather” is a generic term for all hides and skins which have been tanned and finished, but all leather is not the same. It is derived from many types of hides and is tanned and finished in numerous ways.

The cost of the final product is affected by several factors in the selection and processing of the leather. Cost is determined to the greatest degree by the quality, or “selectness” of the hide. The more select a hide is, the fewer the natural flaws it will show. As a general rule, lower price leather will show a greater number of healed scars and other natural markings.

The method of finishing or dyeing also affects the cost of a finished hide. Full aniline dyed leathers, for example, are more expensive because of the difficulty in securing the superior hides required for this process. Leathers which have been antiqued are generally more expensive than machine finished leathers. The popularity of a given color also may affect cost. It is less costly to process large quantity of hides in a single color than to have a few hides finished in custom colors. The savings are passed on n lower priced finished pieces.

Tanning Leather: Although the process of turning hides into leather varies from one tannery to the next, most steps are quite similar. The transformation is accomplished in two basics phases: tanning and finishing. Converting raw hides into a non-perishable state is done in the tanning process.

Initially, the hides are cured in a salt solution which preserves them until the actual tanning begins. The first step in tanning is to clean the hides and soak out the salt. A lime solution is then added to remove hair and flesh. After the hides have been cleaned they are sorted, and those unsuitable for upholstery (due to holes and other defects) are culled out.

The select hides are then split, a process similar to veneering a log. The outer surface of the hide is separated from the lower layers by slicing it with a long blade as the hide is fed through a series of rollers. The outer portion of the hide is referred to as the “top grain” and is usually about 3/64 inch thick.

Manufacturers of quality upholstery use only top grain leathers. The layers beneath the top grain are referred to as split hides, or “splits”; they are generally thicker and stiffer and are used for less expensive upholstery leathers or in industrial applications.

After the top grain leather has been removed it is bathed in a stabilizing solution which alters it chemical structure to prevent deterioration. The resultant product will last indefinitely.

When the hides are removed from the tanning vats, the undersides are “skived” by being passed over a long cylindrical blade. This assures an even thickness across the entire hide. To counter the drying effects of tanning, the hides are conditioned with fatliquors to restore their natural oils and to make them more supple. Once the leather has been stretched and dried it is returned to its soft, supple state by being tumbled in a large drum, or, in some cases, being worked by hand or machine.

When dry, leathers with excessive scarring may be sanded, or “buffed”, to create a smooth surface which can then be finished or embossed with an artificial grain pattern. Embossing makes less select hides usable, thus reducing the cost of the final product. It should be noted that buffing removes the outer portion, or top grain, of the hide. Embossing tend to compress the leather and make it stiffer.

The finest leather available is called “full top grain” leather. This is your assurance that nothing has been done to alter the natural surface of the hide. The more select the is, the less it has to be corrected. Natural variations will be exposed, and the hand or feel will be supple and natural to the touch.

Finishing Leather: Once the leather has been properly tanned and dried, it is colored. The finishing process is the most frequently misunderstood aspect of leather production. Whatever is done to a piece of leather after it has been tanned is part of the finishing process. This may include dyeing, rolling, pressing, spraying, lacquering, antiquing, waxing, buffing, embossing, glazing, waterproofing or flameproofing.

Finishing enhances the natural beauty of the leather, gives it protection, adds color and provides surface appeal. May looks area available to the skilled tanner, but the finishing technique employed is dictated by the nature and quality of the hide itself.

Today’s upholstery leathers have evolved into two distinct types. One bears the glazed, uniform, highly protected surface which the american consumer has come to think of as traditional. Recently, with the influx of European hides into America, aniline dyed leathers have become increasingly popular. This leather is left in its most natural state which accentuates the hides inherent subtle characteristics and supple, velvet hand.

The original selection of the hide will determine if it is to be aniline dyed or topcoated. It is generally accepted that only five percent of the world’s hides supply is of high enough quality for use as aniline dyed upholstery leather. “Aniline dyeing” is the process of soaking the skins in transparent aniline dyes which color or shade the skins without obscuring the natural markings or grain character of the leather. Since aniline dyes do not conceal natural imperfections on the leather surface, only premium select hides can be used.

The skins are immersed in the dyes and tumbled in large drums until the dye has completely penetrated the fiber structure of each skin. They then receive an immersion protection treatment which also penetrates the skins and help shield them against spills and spoilage.

“Aniline-plus” and “semi-aniline” are terms used to define a supplemental step beyond aniline dyeing which adds an opaque pigment and/or protective coating to the surface of the hides.

This type of leather has become very poplar because it combines the softness and feel of full aniline dyed leather with the protective benefits of surface finishing. By dyeing the leather throughout before the final surface coating is applied, a very even coloration can be achieved with only a thin layer of finish, and the leather remains softer.

Machine finished leathers are given an even coloration through a series of finish coats applied by computerized, laser controlled rotary sprays capable of producing many pleasing affects and unique patterns. When a desired colored has been achieved, a clear protective top coat of resin is applied to resist stains and abrasion. Recently developed synthetic resins virtually eliminate the possibility of fading, cracking and peeling; they help to hold the leather’s true color almost indefinitely and are easier to clean. The sheen of this coating can be adjusted to give a gloss, satin or matte surface. Machine finishing is one of the least expensive and most common methods used in producing upholstery leather.

The process of hand antiquing leathers is essentially the same as for machine finishing, except that the final color application is rubbed into the leather by hand. This brings out the natural markings in the hide, such as healed scars or barbed wire nicks, and gives the leather a highlighting which cannot be achieved by machine spraying. Following the color coating, a protective clear finish is applied, as it is to machined finished leathers. Hand antiqued leathers are more expensive than machine finished leathers due to the extra step of hand finishing by skilled craftsman.

Quality Assurance: Produces of quality leather routinely test each batch of furniture grade leather for durability and for resistance to fading in light (of course no furniture covering should be exposed to direct sunlight for extended periods). The leather is also tested for “crocking”, the transfer of color through contact; and for finish adhesion and flexibility , to be certain the leather will not split or crack as time passes. Tear strength is also determined; as mentioned, the natural fiber structure of leather makes is extremely tear resistant. Finally the leather is test for “wear-through”. or abrasion resistance, to ensure that it will last for many years.
Leather Types:

Pure Aniline Dye Calfskin: Calfskins are the most luxurious hides available for leather upholstery; their surfaces are completely free of blemishes. Their acceptance of transparent aniline dyes accentuates the natural grains and fat wrinkles. The resulting depth of color and slight variations occurring throughout the skin make this one of the most desirable leathers for the discriminating buyer. It is impossible to mistake it for synthetic. The surface is protected in much the same way as fabrics are in order to protect the luxurious hand. The sensuous feel is unforgettable. The leather is suitable for all types of periods of upholstered furniture. Aniline Plus Calfskin: Because aniline dyes are transparent, the range of colors is limited. In the aniline-plus process a light coat of pigment is applied to the surface after dyeing to increase the uniformity and range that can be achieved. As a result of this treatment, more hides are acceptable for this category. The pigment application is so thin that it provides a greater degree of protection to the surface without altering the natural softness of the calfskin, which is usually silky smooth to the touch. This leather is suitable for all types and periods of furniture, particularly the soft contemporary styles. It will appeal to the individual who wants the best, but wishes to have a wider selection of color. Pure Aniline Dyed Leather: Premium hides of fully grown animals are used for this application, and only three to five percent of raw hides are free enough of defects to be suitable. In aniline dyeing, an extended tumbling process enhances the natural full grain and gives extra softness. A soil resistant surface coating similar to that used for fabrics is then applied. This lather retains the smooth velvet feel of calfskin, but because the hides are larger and there is less waste, it is less expensive. Aniline dyed leather is suitable for all types of upholstery, and greatly enhances the soft, supple look at contemporary styles.
Aniline-Plus: This is a natural grain leather and its surface must be of good quality with few natural markings. As with all natural grain leathers, the pattern and texture will vary across the hide. These hides remain in the aniline dye vats until the color has completely penetrated the skin. Slight variations in shade occur because the cell fiber structure changes from the backbone towards the perimeters. This is corrected by applying a thin coat of matched-color pigments: hence the term “aniline-plus” or “semi-aniline.” Aniline plus leather has a soft, pleasing hand and lends itself well to all types of upholstery, especially soft styled transitional or contemporary. It falls in a medium price range and is an excellent choice for those who object to the shading variations found in true anilines. Only a limited number of  hides are acceptable for this category of leather. If corrected grain hides are used for this category, their selection is less critical, and the hand will not be soft. Hand Antiqued Leather: Hides used for this category retain enough acceptable markings to identify them unmistakably as true leather. The surface is plated with hair cell grain to level out the neck and fat winkles and to remove the uneven grain. Base coats of color pigments are then applied by machine, but the antique effect can be achieved only by hand rubbing and padding. A heavy glazed coating is next applied to protect the surface. This leather is particularly suited to period and traditional styling., and is a god value. The hand is rather flexible, but not as much as leather without pigments and glazed surfaces. Corrected Grain Leather: Tanners have numerous hide that they have rejected for other categories because of the number of bold scars and insect bites. These hides have their surfaces sanded to remove such imperfection; this also removes the natural grain. A heavy grain pattern is then embossed into the surface under extreme pressure to cover most remaining imperfections. Thick coats of color pigments are next applied to the surface by machine, and a smoke finish completes the camouflaging process.The leather is then given a protective coating and the reverse side is dyed to match the surface. Because of the sanding, embossing and heavy pigments, the hand of the leather is rather boardy. Compared to more expensive leather upholstery, this category is usually associated with promotional price points. Hides that require less correction will have less grain embossed and will be more flexible, though more expensive.
Leather Terms:

  • aniline (an-a-lin) dyed: the process of coloring leathers throughout with transparent dyes.
  • antiqued: the light application of one color over another, (usually a darker color over a lighter color) to create highlights.
  • corrected grain leather: leather whose natural surface texture has been altered.
  • crocking: transferring of color by rubbing
  • 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 color, either by spraying, hand-rubbing or immersion.
  • embossing: a process in which design is added to leathers surface by pressure to alter or enhance the surface, resulting in uniform imitation grain or unique patterns.
  • fatliquors: natural lubricants of leather which maintain softness.
  • finishing: any post tanning treatment, such as: dyeing, rolling, pressing, spraying, lacquering, antiquing, waxing, buffing, embossing, glazing, waterproofing or flameproofing.
  • full grain: a term which indicates that leather possesses its original, natural grain; leather which has not been altered.
  • glazing: synthetic transparent resins applied as a protective coating to leather, providing a high gloss or matte finish; also known as “top coating”.
  • 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 a leather.
  • hides: skins of animals, usually cattle, sheep or water buffalo.
  • leather: a generic term for all hides and skins which have been tanned and finished.
  • natural grain: the unaltered top grain surface of leather.
  • patina (pa-tee-na): a luster that develops with time and use.
  • premium select: a term describing hides with very few scars or blemishes, usually less than 5% of all hides.
  • sanding: refers to the removal of grain, scars and blemishes from a hide’s surface.
  • semi-aniline (an-a-lin): leathers which have been aniline dyed then top coated with matching pigments to even out the color (also called “aniline plus”).
  • skived: a term referring to leather which has been thinned or shaved to assure uniform thickness.
  • splits: underlying layers of leather, usually used for suedes, not top grain.
  • splitting: cutting a hide into two or more layers.
  • synthetic resins: chemical substances used to protect leather.
  • tanning: treating raw hides to reduce their perishability.
  • top grain: the top surface of the hide.
  • tumbling: a process in which hides are tumbled in a rotating drum to soften the hand or enhance the grain.