The most confusing term used in the furniture industry is the term
" top grain'. It can be a contradiction because it often implies what it
is not. "Top grain", is the definition that is generally used when the
grain is not genuine: when the real grain is sanded away and an imitation
grain is stamped into the leather. When the genuine grain remains, the
leather is called, "full grain," or " full top grain, " not simply" top
grain."
Webster dictionary offers nearly a hundred definitions for the word "top".
They include: the highest point,the summit, the best, the upper-surface,
the lid, the supreme, the choicest part, the cream, the pick. It also means
to excel, to surpass, to dominate or to be superior to the rest.
When one hears the term "top grain" it's reasonable to assume it's the best.
But, if the real grain is gone, can that be true? If the real grain was
removed and replaced by an imitation grain, the result is neither the best
nor the uppermost.
If you want the best, insist upon leather which retains the entire original
grain. Insist upon receiving the full grain.
Top grain is generally not the tops!
FULL GRAIN LEATHER
Just as the grain , texture and markings of wood should reveal the nature
of the tree from which it came, leather should display the natural markings
and grain characteristics of the animal from which it was taken. The best
upholstery leathers are clear,clean, and supple. They are also dyed
through with transparent aniline dyes. The full natural grain is retained
and they are called "full grain leather."
Cheaper leather have the natural or genuine grain sanded away and an
imitation grain pressed or embossed into the surface.They are stiff and
"boardy" with a heavy coating of pigmentation to cover up imperfections
and they look and feel much like plastic.
The better the quality of hide or skin, the less it has to be treated.
The natural grain variations should be exposed. One should see the
"fat wrinkles" and the feel, or hand, should be supple and natural to
the touch. So when choosing your leather, make sure it looks natural,
smells good, and has a soft hand. Inspect your leather carefully.
Make certain that it retains the full natural grain.
Full grain leather - it is the tops!
Hides selected for furniture are sliced to a uniform thickness on
precision machines. Only the 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 topcoat finishes. The familiar
"chamois" used in auto care is an example of split leather.
These terms below are classified at the tannery level and are
not grades of leathers used by manufactures. For furniture manufacture
grades, see individual companies for their leather grading structure.
"This information listed here is a grading structure used at the tannery
level and are not grades of leather used by manufactures on their furniture.
For the production of every kind of hides for furnishings, from the most
prized to the most ordinary, hides from various countries and regions are
used. Pig hides are also used in the furniture industry, but this sort of
leather does not meet durability requirements or quality. The place of
origin of raw hides can be divide into three groups.
A. Hides from Southern Germany, Hides from Swiss pastures,
Scandinavian Bull hides from Norway and Finland.
Hides from Northern Italy.
B. Hides from Northern Germany, English hides, Dutch hides,
and North American US hides.
C. Australian Hides, African hides, South American hides,
Hides from Asia.
Raw Material
Today we think of leather as a commodity, something that is pretty much the
same everywhere. Not true.Leather for furniture comes mostly from cattle
and no two hides are alike. Age, heredity, and the environment all influence
the character of leather. Leather is the strongest most versatile natural
resource. It should be understood that cattle leather is a byproduct of
the meat industry, and are raised for beef consumption. Leather is a
renewable resource, so it allows us to create valuable products out of what
otherwise would be waste. The largest sources of cattle hides are the beef herds of North
and South America.
TANNING PROCESS
RAWHIDES
- Contain high amount (about 70%) of water and become hard and
inflexible after drying.
- Can be easily attacked by bacteria and rot. They have to be kept
refrigerated or the water removed by some means (not very useful for
making into upholstery!)
- Are dirty with blood, dung, etc., sticking to it and contain hair and
other materials which are not needed.
For making into upholstery, the leather should be
- Dry and flexible
- Stable
- Should have color, softness and other properties for the specific
use.
Tannery operations achieve the above changes.
Tanning makes the leather fiber resistant to bacterial attack.
Nowadays, chrome tanning is the most popular method. The modern leather
processing can be divided into three parts:
- Preparation of wet blue (chrome tanned leather)
CHROME TANNING.
- Modification of the properties as needed in the final leather.
- Finishing on the surface.
Most of the processes in 1 and 2 are done inside drums (or other
vessels) as batch operations in water (orange colored in the text) and a
few operations are carried out in special machines on individual
hides/skins
Preparation of wet blue (chrome tanned leather)
The first job in the tannery is to give
the hides a good wash, with water, some special detergents and some
other chemicals. This is called Soaking
Any loose flesh (remember, hides are taken from animals killed for
meat!) sticking to the flesh side is scraped off by a knife (using a
specially designed machine). This is called Fleshing.
Unhairing
removes the hair on the skin using certain chemicals,
which can eat away the hair but not the hide fiber.
The chemicals used to tan the hides and modify the color, softness
and other properties should be able to penetrate into the fiber network.
The fiber network should be opened up and most other non-fibrous
material removed. This is done in Liming. A process is used that requires a special soaking which uses alkali (lime) to increase the water
entering the fiber network. Natural grease is also removed in this
alkaline solution.
Normally, for the production of upholstery leathers the hides are
split in to two layers in a machine using flat knife. The primary
purpose of this operation is to make the thickness of the hide uniform
throughout. Originally the hide is thickest in the neck portion of the
animal and thinnest at the belly portion. The top layer, which is
stronger and of uniform thickness, is used for making upholstery
leather. The bottom layer is of non-uniform thickness and processed for
different uses.
Then a series of adjustments in the acid/alkali balance (pH) of the
hide is done before applying the chrome tanning salts. These operations
are called Deliming and Pickling.
Chrome tanning salts penetrate the hide and react chemically with the molecules, making the fiber network
resistant to bacteria. Modification of the properties as needed in the final leather product.
The main properties modified here are:
- Leather Thickness
- Color
- Softness
A number of other characters can be changed depending on the type of
the leather being made by using specific chemicals.
Thickness is reduced by a Shaving
machine, which shaves some thickness off from the back of the hide to make it more uniform in thickness.
After adjusting the pH balance, further chemical treatments are carried out.
Retanning
uses special plant material or synthetic material to
modify a range of properties. Dyes used in dyeing, color the fibers
of the leather. Specially prepared oils are used in fatliquoring to make
the leather soft (the oils lubricate the fibers). Special requirements
such as water proofing, flame proofing, solvent resistance etc. can be fulfilled at this stage.
The leathers are stretched and flattened in Setting Machine and dried. After drying the leather is subjected to mechanical
operations to make it soft, flat and tight. Either side can be modified
by emery paper on a buffing machine.
FINISHING ON THE SURFACE.
A wide variety of finishing operations is
carried out on the leather surface. The most common type is coating with
colored mixes. Also worth mentioning is buffing the leather surface with
emery (sandpaper) to get a suede or nubuck surface (velvet like surface)
and an application of oils and waxes to get a pull up effect. You can see the
different types of finishing done on upholstery leathers in the section
on types of leathers.
Finishing modifies the surface color, gloss, and the final appearance
of the leather. It also provides a protection to the surface from water,
wear and abrasion.
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