How is leather made?
The principal process of making leather hasn’t varied that much over the years, but that doesn’t mean it is simple. However, do you know how leather is made? Did that question ever knock in your mind? Well, there are some initiatives before making a leather ready to use. Tanners are highly trained in what they do though it is surprisingly a complicated and lengthy process!
To transform a salted skin to a piece of leather ready for use takes a minimum 20 working days!
The steps below will make you clear about what tanneries have to do to turn hides into leather:-
Rawhides and skins must be preserved to stop them from deteriorating before the leather-making process start. There are several methods of preservation as salting, chilling, freezing and the use of biocides.
Cured pelts or skins are soaked in water for a couple of hours to several days. This allows the hides to reabsorb any water they may have lost in the curing process or during transportation. It also helps to clean the salt and dirt of the hides.
Painting is a process to remove the wool from sheepskins using a sulfide-based mixture.
By liming the epidermis and hair from the skins are removed. This also results in alkaline swelling of the pelt to cause a controlled breaking of some of the chemical crosslinks of the collagen.
After liming, the pelt pass through a machine to remove fleshy tissue from the flesh side. Hides are sometimes split into layers at this stage.
The main task of deliming is to slowly neutralize the alkali in the pelt, avoiding rapid changes in pH which could cause distortion or disruption of the leather tissues.
Along delime can significantly improve the removal of any remaining lime, scud (miscellaneous debris) and residual components broken down during liming. Bating – based on the use of enzymes – completes this process so that the pelt is flat, relaxed, clean and ready for pickling and tanning.
Weak acid and salt solutions are used to bring the pelt to the weakly acid state required for most tanning processes. Stronger pickling solutions are used to preserve pelts so that they can be stored or transported in a stable form over periods of several months.
Solvents or water-based systems can be used to remove excess grease before tanning.
Splitting is a process where thicker leather is sliced into two layers.. The layer without a grain surface can be turned into suede. It also has an artificial grain surface applied. A splitting machine slices the leather according to the thickness you set on it.
A uniform thickness is achieved by shaving the leather on the non-grain side using a machine with a helical blade mounted on a rotating cylinder.
Neutralising removes residual chemicals and prepares the leather for further processing and finishing. Additional tanning material may be applied to give particular properties which are required in the finished leather.
The dyeing of leather into a wide variety of colors plays an important part in meeting fashion requirements. Some leathers are the only surface dyed, while others need completely penetrated dyeings, as is the case with suede leathers.
Fatliquoring introduces oils to lubricate the fibers and keep the leather flexible and soft. Without these oils the leather will become hard and inflexible as it dries out.
This process reduces the water content to about 55% and can be achieved by a number of machines, the commonest being like a large mangle with felt covered rollers.
The leather is stretched out and the grain side is smoothed. This process also reduces the water content to about 40%.
The leather is normally dried to 10-20% water content. This can be achieved in a number of ways and each method has a different effect on the finished leather:
Staking and dry drumming
A staking machine makes the leather softer and more flexible by massaging it to separate the fibers. To finish off the leather may be softened by the tumbling action inside a rotating drum.
Buffing and Brushing
The flesh surface is removed by mechanical abrasion to produce a suede effect or to reduce the thickness. In some cases, the grain surface is buffed to produce a very fine nap, e.g. nubuck leathers. After buffing the leather is brushed to remove excess dust.
Tanning converts the protein of the raw hide or skin into a stable material, which will not putrefy and is suitable for a wide variety of purposes. Tanning materials form crosslinks in the collagen structure and stabilize it against the effects of acids, alkalis, heat, water and the action of micro-organisms. The main types of tanning materials are:
Most leather is tanned using salts of chromium. This is known as the mineral tanages
Aldehyde and oil tannages
Aldehydes and oils are used to produce very soft leathers and this tanning method also creates leather articles that is dry-cleanable, washable fashion leathers and also chamois leather.
Different sorts of vege extracts produce brown-colored leathers that tend to be thick and firm. This type of tannage is used to produce for shoe linings, bags, stout sole leather, belting leather and leathers and cases.
The aims of finishing are to level the color, cover grain defects, control the gloss and provide a protective surface with good resistance to water, chemical attack, and abrasion.
Sorts of Finished leather: Full Chrome crust leather, Semi-chrome crust leather, Full vegetable crust leather, Semi vegetable crust leather, Lining crust leather, Ecological Crust Leather, Nappa leather and candy leather.
Leather will be graded before despatch to the customer. This grading may consider the color intensity and uniformity, the feel of the leather, softness, visual appearance, thickness, design effects and natural defects such as scratches.
Wrapping It Up
So after going through all the stages, leather is ready to use. People use leather to make different kinds of goods ie: shoes, slippers, hats, belts, wallets, jackets, bags, furniture covers and etc wearings. Howsoever, the leather product that you use has to pass through the above described time-consuming steps. After a piece of hide passes those steps, they are ready to utilize.