The History of Leather
Leather has been used by mankind for centuries. It is an ancient product that served
functionally and as a sign of status long before The 20th century. Modern technology has not yet been able to duplicate genuine leather.
Leather comes from the skins of animals. America is both the largest producer and the
largest consumer of leather products. Cattle, As our largest source of leather, provides
almost 75% of the leather used today.
Since cowhides are a by-product of meat consumption, we'll have hides as long as people
eat meat. While cowhide leather is produced in various finishes, thickness, splits,
colors and shades, it's almost always identified simply as cowhide. The next most
important source of animal hides for the leather industry is sheep and lamb. Sheepskins
are also known by several other names, such as Cabretta, Shearling, French Antelope and
Mouton. Other animal whose hides are used for leather are goat, horse, elk, deer, pig,
alligator, snake, shark, ostrich and lizard. These hides however, make up a small
percentage of all leather.
Leather has many desirable qualities: It's tough, almost indestructible; it's comfortable
to wear, being made soft and supple with tanning; it molds to the foot's shape with wear
and it breathes to keep the wearer comfortable; and it's versatile. The scent, sight and
feel of genuine leather adds to its desirability, and the demand for quality leathers
continues to rise.
Leather garments generally fall into two categories: Suede Leather and Grain leather.
Suede
Normally suede refers to the flesh side of pigskin or sheepskin. These skins will vary
in thickness, depending on the time of the year they are harvested. In winter they are
thicker. Most sheep raised in the U.S. are larger and have thicker hides than those
grown in Australia, New Zealand and England.
To make a garment which is of the same thickness throughout, the heavier part of the
skins (the neck and back) are split away. Since a skin is made up of three layers and
all three layers are required to keep the skin at full strength, the more that is split
away, the less strength the skin retains. The softest, most pliable garments are made
from skins that have been split very thin
Sueded Split Cowhide
When the heavy part of cowhide is split off to make the remaining hide even, the flesh
side of the portion split off can be sueded. Caution is taken not to make the split too
thin because it might lose its tensile strength.
Grain
This is the slick side of the skin, or the hair side with the hair
removed. There is a large variety of grain leathers, each offering attractive features.
For example, cow grain is a very practical leather; Cabretta doesn't scuff easily; Glazed
lamb can be wiped off with a damp cloth, but is stiffer than naked lamb, cow grain or
Cabretta, while any naked leather will look and feel great, it will soil easily, be more
difficult to clean and will present color variations.
The Tanning Process
Tanning transforms raw animal hides into finished leather for use in making leather
products. A highly technical series of chemical and mechanical processes converts raw
skins into finished leather. In all, the processes take several weeks. In the processing,
the tanner strives for the feel of the leather, called "a good hand." The
finished skin must arouse a perception of beauty and have the natural feel of leather.
Different animal pelts have various noticeable characteristics. Calfskin looks different
than pigskin which, in turn, looks different from sheepskin. There are less obvious
differences present in the unique physical properties inherent in different animal skins.
These Differences are the basis for selecting leathers for specific uses.
Prior to tanning, hides must be cured so they won't decompose and become useless. The
principle curing agent is salt, and two methods of Curing are used:
1.Salt Wetting. The flesh side of the hide is sprinkled with granular salt and
hides are stacked atop one another and left for several days until the salt completely
dissolves into the skin moisture and penetrates the hides.
2.Brine Curing. This is a faster method of curing. The hides are soaked in
brine for about 12 hours, drained, sprinkled with additional salt and bundled for shipment
to the tanner.
The Actual Tanning Process Involves 16 Steps:
Step 1. Trimming & Sorting
Each hide is inspected and all areas such as heads and shanks that would not make good
leather are cut off. To make the cowhides easier to handle, each is cut lengthwise along
the backbone from head to tail to make two sides, termed "sideleather." Each
is approximately 20 square feet. It takes about 16 square feet to make a pair of boots
and 23 to 39 square feet to make one man's jacket.
Step 2. Soaking
As a result of the curing process, the hides have lost a
good deal of their natural moisture. They are now soaked in wetting agents for up to 20
hours to restore some of this moisture. After the soaking process, they are washed to
remove any excess salt, dirt or blood from the skins.
Step 3. Fleshing
This is a mechanical operation that removes any excess flesh, fat or muscle on the
flesh side of the skin.
Step 4. Unhairing
Through a chemical process, all the hair is removed from the grain side of the hide.
This process takes just a few hours.
Step 5. Bating
This creates a softer feeling to the grain surface and gives it a
cleaner appearance.
Step 6. Pickling
Pickling adds salt and then acids to the hides. This operation is a preserving technique
so that the skins can be kept for extended periods of time without deterioration.
Step 7. Tanning
The primary function of any tanning agent is to convert the raw fibers of the hide into
a stable product which is no longer susceptible to decomposition. Tanning also improves
stability, abrasion resistance, the ability to flex innumerable times without breaking,
and the ability to endure repeated cycles of wetting and drying. The method of chrome
tanning is used most because it produces leather most sought after in the majority of
leather uses. Oil tanning is used for work boot leathers and vegetable tanning for many
dress boot leathers This tanning process takes 4-6 hours.
Step 8. Wringing
At this stage, all the excess moisture is removed so the hide can be properly handled
for splitting.
Step 9. Splitting
Thickness within hides often varies, and if not corrected will
cause leather manufacturers problems. Hides are fed through a machine outerside up so that
part of the underneath, or flesh layer is cut off. This process produces two types of
leather from one hide: Grain, which is the hair side, and split, which is the cut off,
underneath side of the grain.
Step 10. Coloring
The natural beauty of leather is enhanced with the art of dyeing. There are basically
two dyeing methods used: Drum dyeing and spray dyeing. In drum dyeing, the more widely
used process, the dye is put in dyeing drums and the leather is toggled and stretched
so the dye goes all the way through the leather, like staining wood. Splits, suedes and
top grains are drum dyed. Spray dye is used only on grain leathers.
Step 11. Drying
Several different drying methods are: Hanging, toggling, pasting and vacuum.
Hanging:
The hide is draped over a line to dry naturally.
Toggling:
The hide is stretched, clipped on boards and channeled
into drying ovens.
Pasting:
The hide is pasted to plates of stainless steel or oven
glass and passed through equipment that cleans and dries them. This method is the most
popular, as it gives the tanner more yield, or more square feet of leather per hide than
any other type of drying.
Vacuum:
One of the newest methods, vacuum drying places the hide
on a heated stainless steel plate, where it is covered by felt or cloth. A vacuum then
extracts water from the leather.
Whatever the method, all drying must be done very carefully so
that excess moisture is not taken from the hides, which would cause excess shrinkage later
on. Normal leather will contain 10-12% moisture.
Step 13.Conditioning
This step governs the final firmness or softness of the leather.
The leather is stretched and flexed in all directions to help condition it and also to
check the strength of the leather.
Step 14.Buffing
When the skins are of poor quality and have many scars, the tanneries will sometimes
buff the grain side of the skin and then spray a finish over the top. This will make
the skin quite stiff and therefore it will be used in less expensive garments. This
leather is sometimes called "corrected leather." Most leather skins have
natural healed markings called scars or grub marks. In most cases, these markings
actually enhance the authenticity and beauty of the leather, and do not affect
the strength or value of the skin at all.
Step 15.Finishing
In this step, a light coating of transparent materials is applied to the skins to
provide abrasion and stain resistance and to enhance the colors of the leather. This
step may be eliminated on some leathers, leaving the leathers "naked." Naked
leathers will absorb moisture, scratch more easily and soil more quickly than finished
leather.
Step 16.Grading
The final step in tanning is grading to see which are
"select" leathers. Leather is graded for temper, uniformity of color, thickness
and the extent of any defects in appearance. The most perfect leathers naturally command
the highest price and are ultimately cut into the finest merchandise.
After several weeks in the tanning process, the leather is sent to
the manufacturer to be transformed into finished products. Most leather is not made by
tanneries for stock, but is made to order, by color, quality and thickness.