Maybe Too Much Information about Leather
Information reproduced from Wikipedia - More than you probably wanted to know!
Leather is a material created through the tanning of hides and skins of animals, primarily
Cattle hide. The tanning process converts the putrescible skin into a durable, long-lasting and versatile natural
material for various uses.
There are a number of processes whereby the skin of an animal can be
formed into a supple, strong material commonly called Leather.
- Vegetable-tanned leather is tanned using
(hence the name "tanning") and other ingredients found in vegetable
matter, tree bark, and other such sources. It is supple and brown in
color, with the exact shade depending on the mix of chemicals and the
color of the skin. Vegetable-tanned leather is not stable in water; it
tends to discolor, and if left to soak and then dry it will shrink and
become less supple and harder. In hot water, it will shrink drastically
and partly gelatinize, becoming rigid and eventually brittle.
Boiled leather is an example of this where the leather has been
hardened by being immersed in hot water, or in boiled
similar substances. Historically, it was occasionally used as
after hardening, and it has also been used for
book binding. This is the only form of leather suitable for use in
leather carving or stamping.
- Chrome-tanned leather, invented in 1858, is tanned using
chromium sulfate and other salts of
chromium. It is more supple and pliable than vegetable-tanned
leather, and does not discolor or lose shape as drastically in water as
vegetable-tanned. It is also known as wet-blue for its color derived
from the chromium. More esoteric colors are possible using chrome
- Aldehyde-tanned leather is tanned using
oxazolidine compounds. This is the leather that most tanners refer
to as wet-white leather due to its pale cream or white color. It is the
main type of leather used in chrome-free leather often seen in infant's
shoes and in automobiles made with chrome-free leather.
Formaldehyde tanning (being phased out due to its danger to workers
and the sensitivity of many people to formaldehyde) is another method of
aldehyde tanning. Brain-tanned leathers fall into this category and are
exceptionally water absorbent. Brain tanned leathers are made by
a labor-intensive process which uses emulsified oils, often those of
animal brains. They are known for their exceptional softness and their
ability to be washed. Chamois leather also falls into the
category of aldehyde tanning and like brain tanning produces a highly
water absorbent leather. Chamois leather is made by using oils
(traditionally cod oil) that oxidizes easily to produce the aldehydes
that tan the leather.
- Synthetic-tanned leather is tanned using aromatic
such as the
Neradol types. This leather is white in color and was invented when
vegetable tannins were in short supply, i.e. during the Second World
War. Melamine and other amino-functional resins fall into this category
as well and they provide the filling that modern leathers often require.
resins were also used in this tanning method until dissatisfaction about
the formation of free formaldehyde was realized.
- Alum-tanned leather is tanned using
salts mixed with a variety of binders and
sources, such as flour, egg yolk, etc. Purists argue that alum-tanned
leather is technically "tawed" and not tanned, as the resulting material
will rot in water. Very light shades of leather are possible using this
process, but the resulting material is not as supple as vegetable-tanned
- Rawhide is made by scraping the skin thin, soaking it in
lime, and then stretching it while it dries. Like alum-tanning,
is not technically "leather", but is usually lumped in with the other
forms. Rawhide is stiffer and more brittle than other forms of leather,
and is primarily found in uses such as
drum heads where it does not need to flex significantly; it is also
cut up into cords for use in lacing or stitching, or for making many
varieties of dog chews.
Leather, usually vegetable-tanned leather, can be oiled to improve its
water resistance. This supplements the natural oils remaining in the leather
itself, which can be washed out through repeated exposure to water. Frequent
oiling of leather, with
Neatsfoot oil or a similar material, keeps it supple and improves its
lifespan dramatically. Leather with the hair still attached is called hair-on leather.
In general, leather is sold in three forms:
- Full-Grain leather or Top-Grain is referring to the
upper section of a hide that contains the epidermis or skin layer. It
refers to hides that have not been sanded, buffed or snuffed (otherwise
known as Corrected) in order to remove imperfections on the surface of
the hide. Only the hair has been removed from the epidermis. The grain
remains in its natural state which will allow the best fiber strength,
resulting in greater durability. The natural grain also has natural
breathability, resulting in greater comfort for clothing. The natural
Full-Grain surface will wear better than other leather. Rather than
wearing out, it will develop a natural "Patina" and grow more beautiful
over time. The finest leather furniture and footwear are made from
Full-Grain leather. For these reasons only the best raw hides are used in
order to create Full-Grain or Top-Grain leather. Full
grain leathers can mainly be bought as two finish types:
- Corrected-Grain leather is any Top-Grain leather that
has had its surfaces sanded, buffed or snuffed in order to remove any
imperfection on the surface due to insect bites, healed scars or brands.
Top-Grain leather is often wrongly referred to as
Corrected-Grain. Although Corrected-Grain leather is made
from Top-Grain as soon as the surface is corrected in any way the
leather is no longer referred to as Top-Grain leather. The hides
used to create corrected leather are hides of inferior quality that do
not meet the high standards for use in creating aniline or semi-aniline
leather. The imperfections are corrected and an artificial grain
applied. Most Correct leather is used to make Pigmented leather as the
solid pigment helps hide the corrections or imperfections. Corrected
grain leathers can mainly be bought as two finish types:
leather is leather that is created from the fibrous part of the hide
left once the Top-Grain of the raw hide has been separated from
the hide. During the splitting operation the grain and drop split are
separated. The drop split can be further split (thickness allowing) into
a middle split and a flesh split. In very thick hides the middle split
can be separated into multiple layers until the thickness prevents
further splitting. Split leather then has an artificial layer applied to
the surface of the split and is embossed with a leather grain. Splits
are also used to create Suede. The strongest suede are
usually made from grain splits (that have the grain completely removed)
or from the flesh split that has been shaved to the correct thickness.
Suede is "fuzzy" on both sides. Suede is less durable than top-grain.
Suede is cheaper because many pieces of suede can be split from a single
thickness of hide, whereas only one piece of top-grain can be made.
However, manufacturers use a variety of techniques to make suede appear
to be full-grain. For example, in one operation, glue is mixed with one
side of the suede, which is then pressed through rollers; these flatten
and even out one side of the material, giving it the smooth appearance
of full-grain. Latigo is one of the trade names for this product.
A reversed suede is a grained leather that has been designed into the
leather article with the grain facing away from the visible surface. It
is not a true form of suede.
Other less-common leathers include:
Buckskin or brained leather is a tanning process that uses
animal brains or other fatty materials to alter the leather. The
resulting supple, suede-like hide is usually smoked heavily to prevent
it from rotting.
Patent leather is leather that has been given a high gloss
finish. The original process was developed in Newark, New Jersey, by
inventor Seth Boyden.
Patent leather usually has a plastic coating.
Shagreen is also known as Stingray skin/leather.
Applications used in furniture production date as far back as the
art deco period. The word "Shagreen" originates from France and is
commonly confused with a shark skin and stingray skin combination.
- Vachetta leather is used in the trimmings of
handbags, popularized by
Louis Vuitton. The leather is left untreated and is therefore
susceptible to water and stains. Sunlight will cause the natural leather
to darken in shade, called a
- Slink is leather made from the skin of unborn calves. It is
particularly soft, and is valued for use in making gloves.
- Deer Skin is one of the toughest leathers, partially due to
adaptations to their thorny and thicket filled habitats. Deerskin has
been prized in many societies including indigenous Americans. Most
modern deer skin is no longer procured from the wild, with "deer farms"
breeding the animals specifically for the purpose of their skins. Large
quantities are still tanned from wild deer hides in historic tanning
towns such as Gloversville and Johnstown in upstate New York. Deer skin
is used in jackets and overcoats, professional sporting equipment as well as high quality personal accessories like handbags
and wallets. It commands a high price due to its relative rarity and proven
Nubuck is top-grain cattle hide leather that has been sanded or
buffed on the grain side, or outside, to give a slight nap of short
protein fibers, producing a velvet-like surface.
There are two other descriptions of leather commonly used in specialty
products, such as briefcases, wallets, and luggage.
- Belting leather is a full grain leather that was originally
used in driving pulley belts and other machinery. It is often found on
the surface of briefcases, portfolios, and wallets, and can be
identified by its thick, firm feel and smooth finish. Belting leather is
the only kind of leather used in luxury products that can retain its
shape without the need for a separate frame; it is generally a
heavy-weight of full-grain, vegetable-tanned leather.
Nappa leather, or Napa leather, is chrome-tanned and is
extremely soft and supple and is commonly found in higher quality
wallets, toiletry kits, and other personal leather goods.
The following are not 'true' leathers, but contain leather material.
Bonded Leather , or "Reconstituted Leather", is not really a
true leather but a man-made material composed of 90% to 100% leather
fibers (often scrap from leather tanneries or leather workshops) bonded
together with latex binders to create a look and feel similar to that of
genuine leather at a fraction of the cost. Bonded leather is not as
durable as other leathers, and is recommended for use only if the
product will be used infrequently. One example of bonded leather use is
in Bible covers.
Bicast leather is a man-made product that consists of a thick
layer of polyurethane applied to a substrate of low-grade or
reconstituted leather. Most of the strength of bicast leather comes from
the polyurethane coating. Bicast was originally made for the shoe
industry and recently was adopted by the furniture industry. The
original formula created by Bayer was fairly strong, but creating Bicast
from the original recipe is expense. Most of the Bicast used today is
created using inferior generic chemicals resulting in an inferior
material. The result is a much stiffer product that tends to delaminate
resulting in bubbles and cracking.
The vast majority of leather is sold according to its area. The unit of
measurement is square meter, square decimeter or square foot. The thickness
is also important, and this is measured using a thickness gauge (the unit of
measurement is millimeters, e.g., 1.8 mm is a standard thickness for a
school shoe). In some parts of the world top-grain thicknesses are described
using weight units of ounces. Although the statement is in ounces only, it
is an abbreviation of ounces per square foot. The thickness value can be
obtained by the conversion: 1 oz/ft2 = 1/64 inch (0.4 mm), hence, leather
described as 7 to 8 oz is 7/64 to 8/64 inches (2.8 to 3.2 mm) thick. The
weight is usually given as a range because the inherent variability of the
material makes ensuring a precise thickness very difficult.
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