Leather is among one of the earliest discoveries of man. For thousands of years the process of leather production has been followed. Leather is a flexible material made by the skin and hides of animals for the purpose of manufacturing different consumer items, such as jackets, footwear, bags, sports items etc. There are many materials to choose from when it comes to leather making as every material has its own characteristics. Cowhide is one of the most widely used materials in leather manufacturing.
The process of leather manufacturing is divided into 3 steps: preparatory stage, tanning, and crusting. In addition to these steps, finishing is also a part of the process for some but not all leather.
Preparatory Stage:
After the raw material has been sourced, the first production stage begins, where all the necessary work is done to prepare the hide for the tanning process. It includes soaking the hide which is performed by dumping hides into large water drums to remove excess salt that has been applied to the hides when they are shipped to the tanneries to prevent them from decomposition, the process of removing excess salt is essential to protect them for dehydration, after that the hides goes through a series of step such as hair removal, limingand degreasing (applying of chemical substances on hide to increase its flexibility and softness, and splitting (dividing the hide into two layers; the grain-top layer and the suede-bottom layer), also known as cleansing phase. The process can take up a period of 6 hours to 2 days.
Tanning Stage:
It’s the preservation process where the protein structure of the animal hide or skin is altered to make it less receptive to decomposition and more durable in nature. The prime difference between raw hides and tanned hides is that the former is dried out to form a firm, rigid and inflexible material which is easily putrefied whereas after the tanning process these features are altered into forming a flexible and durable material.
The tanning process begins with soaking the hide in water so that it can be cleaned and softened. Next, in order to reduce the moisture, the hide is treated with salt to inhibit the growth of bacterias and to preserve it for a longer period of time. The hide is then soaked once more to remove the excess salt. To complete the tanning process, the hide is treated with lime water to debilitate hair and other unwanted material on hide. Until the POH of the collagen in the skin is at the optimal level the hide keeps undergoing multiple materials. However, you would be surprised to know that even in tanning there are different methods.
The two of the widely used methods are:
Vegetable Tanning:
Vegetable tanning is gaining more preference in the leather industry as it has no unfavorable impact on the environment and is said to be biodegradable. The vegetable method is among the oldest method that involves natural tannins in the tanning process. However, the process requires skilled craftsmen and a longer duration to produce (30 – 60 days), making it valuable and expensive at the sametime. The leather processed through vegetable tanning is slightly stiff and low in flexibility and functional factors. Moreover, the colors of chrome tanning leather lasts for more days whereas, vegetable tanned leather darken overtime but has a long lifespan.
Chromium Tanning:
The tanning process which is done through chromium salt is known as chromium tanning process. The process is cheap and quick compared to other methods and the leather can be easily produced in a single day therefore it is found to be cheaper and in abundance than vegetable tanned leather. The orientation of leather is softer compared to Vegetable-tanned and is available in a variety of colours. Moreover, leather processed through chrome tanning is fairly resistant to water, stains and heat. It works best for leather products that require fire resistance and oil repellency. Working with chrome tanned leather has its perks when it comes to mass production because vegetable extracts resources are scarce.
Crusting & Finishing Stage:
The leather remains in its unfinished condition even after the process of tanning. Because of its uneven thickness and edgy form along with varying degrees of moisture in the hide. To provide an optimal level of thickness to hide a process of thinning and greasing leather is performed which is called crusting. The finishing stage further on involves dyeing, re-tanning (additional tanning to modify leather for final use), drying (the hides are stretched dried on large frames) and trimming (giving a finish and smooth to the edges of leather).
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