Leather's long journey
Leather is one of the earliest crafts, dating back thousands of years - from the Egyptiansto the Ancient Greeks, from the Romans to the Middle Ages. The hides (from large animals) and skins (from small animals) come from many partsof the world - from Europe, Australia, Brazil, Russia & the USA.
Hides are a by-product of the meat industry. The leather life cycle is usually as follows: farm, abattoir, tannery, factory, retailer, consumer.
What happens when the hides are removed from the animal and sent to the tannery?
The first process performed is to shake out the salt, avoiding pollution of the water system. Leathers are then soaked in lime in a process called liming. This chemically dissolves the hair, removes unwanted proteins and opens up the fiber structure.
This process swells the leather considerably.
Remembering that this material comes from an animal, it still has fleshy parts to it.
Therefore, the next process is fleshing. The fleshing machine has many cutting blades on a revolving cylinder that cuts away unwanted fleshy matter and regularizes leather thickness.
The leathers pass on to the next stage called trimming, where workers cut away useless or unwanted material from the edges of raw hides to give them a better shape or 'trim'.
A very important operation then takes place called splitting. As the leather is still of a thick dimension, this is the operation of cutting a hide or skin horizontally into two layers.
The upper layer, the more external part of the animal, is called top grain and the lower layer is called split.
The tanning process
In this case, the hides are placed inside a rotating wooden drum specially designed for tanning.
Tanning agents convert the raw fibers of the hide into a durable product, preserving it, improving its abrasion, heat and flex resistance, able to endure repeated cycles of wetting and drying without degradation.
Next, two large rollers squeeze out the excess moisture as the hides are fed through a machine. This is termed wringing. The leathers are now called 'wet blue'.
The leathers may now be selected or graded as desired, according to the destination of use. Once they have been selected, they need to be reduced and made uniform in thickness. This is done by a shaving method, normally a machine with a rapidly revolving bladed cylinder.
The leathers are then retanned and dyed through, literally a further tanning treatment to modify leathers' properties. The leathers that exit here are now uniformly dyed. The natural beauty of leather is made even more striking by the wide variety of shades which the modern tanner is capable of producing.
The last of the wet operations is the fatliquoring to grant leather permanent softness, elasticity and flexing resistance.
The drying operations
The first step is setting-out a working over the grain surface to remove excess water and eliminate wrinkles.
Leather drying can be continued by various methods.
One of these is vacuum drying where leathers are put on a large, hot, flat plate and another plate presses down and sucks the water out of the leather by creating a vacuum. This is a very effective method.
Or there is toggling - leathers are fixed on frames with toggles, or clamps. The leathers then go through a dryer. This stretching can be done manually or automatically.
Another method is suspension drying. The hides are suspended from the ground on a wire or chain so that air has free access to both sides and they move high up around the tannery complex. In this way, the leathers dry at room temperature.
Leather is staked to make it open and softer. Pins pound the leather from both above and below, hundreds of times, as it passes through the machine, stretching and flexing the leather in every direction. This softens the leather remarkably.
Classification of hides is an important action that requires long experience
Normally the hides are sorted in 4 different levels, which becomes normative for what kind of leather will be produced. From the first-rated hides, with as few natural defects and damages as possible, aniline/natural leather is made, that expresses the natural look and the soft feeling.
The lowest-rated hides, with lots of scars, wounds and damages are normally used for pigmented leathers which have been sealed with stucco, pigmented and embossed to hide the defects that this classification of leather has.
From the middle-rated leathers, semi-aniline, pigmented leathers etc, with different looks and qualities are produced, according to the customers wishes.
Some skins have natural healed scratches or parasitic damage in the grain of the leather. A very special, flexible paste stucco can fill in such gaps. Buffing or 'sanding' leaves a clean, smooth surface ready for the subsequent finishing operation.
The finishing
The finishing department is the area where an alert and creative mind adds the final touches to enhance the natural beauty of leather.
Rotary spray
One method of applying the finish is the rotary spray: Several spray guns are mounted on a unit which continuously revolves over the leather. Unique patterns and two-tone effects can be obtained.
Rollercoater
Another application method is through the rollercoater: the finish is transferred directly from a steel roll to the leather surface. Once the leather is dry, an artificial grain pattern is often created by embossing the leather, using etched or engraved rolls. Grain pattern and softness can be further enhanced by dry milling the leather.
Bycast
Bycast is a completely different system of finishing or enhancing leather (usually split leather or heavily buffed leather) maintaining the same thickness and softness. The technique consists of creating the finishing film on a continual support of release paper. An adhesive is applied to the film and then the film is pressed on the leather. The finished leather is then removed from the release paper displaying a perfectly uniform surface.
Before being delivered to the customer, the leather is measured by a very precise machine.
