BDT ৳ 
Different types of leather: Prior to understanding leather, let us understand animal skin. The inside of the animal skin covers flesh and the outside is exposed to the environment. The outer surface of animal skin besides hair also has grains – densely arranged dead cells that form a specific pattern due to tightly-packed sturdy fibres mostly of collagen. The tough grains on the outer surface offer protection against foreign agents and environmental conditions. The inner layer is known as dermis or corium – which is less densely pack on the inner side (collagen fibres are flexible and thinner) compared to the outer side (collagen fibres are tight and thicker). The corium becomes thicker and tighter as it approaches close to the grain. Collagen fibres in this layer offer strength and elasticity. As an animal ages, the corium becomes thicker, denser and tougher – owing to this reason calfskin is softer, smoother and thinner than the skin of older animals. In a nutshell, grain and corium are the two layers of animal skin or animal hide.
While buying leather products, as a consumer, you should know what you are buying and is it worth paying for the product you want to buy. The things to remember while buying leather include knowing proper terminology and types of leather and the ability to spot differences among different types of leather.
Grain leather
Grain leather is of two types: Top grain leather and full grain leather.
Top Grain Leather: This type of leather is corrected in some or the other way. It is called as top grain leather.
Full Grain Leather: In this type of leather, the entire grain is kept completely intact with all the blemishes, scars, stretch marks and bands. In spite of all such blemishes and marks, this type of leather is in high-demand and even expensive. Owing to its longevity and durability, it is the most sought-after leather across the globe.
The grain leather is further classified into three types: aniline, semi-aniline and protected.
Aniline leather: To obtain this type of leather, animal hide (skin) is processed with soluble dyes. This type of processing retains the texture and natural marking of the leather without requiring surface coating or pigments. Aniline leather is the most natural looking leather. However, it is prone to staining, fading and scratching.
Semi-aniline leather: To obtain this type of leather, animal hide (skin) is treated with pigments to conceal blemishes and obtain uniform coating. This type of leather stays more protected.
Protected leather: This type of grain leather is protected with a non-leather coating, which is sprayed as a protectant.
Split leather: This type of leather is known to us by different names. The layer of skin that is split off from the corium and grain junction – which is less densely pack on the inner side (collagen fibers are flexible and thinner) compared to the outer side (collagen fibers are tight and thicker) is known as split leather. This is the most confusing type of leather for a layperson. It is most often referred to as genuine leather. However, there is no consistency in the usage of this term. Genuine leather is mostly used to mean real leather to differentiate it from the manmade faux leather. Though split leather is the appropriate term, there are several terms used to refer this type of leather, such as coated leather, embossed leather, Suede leather, corrected leather, painted leather and Napa leather.
Split leather is processed into a finished split to make it durable and strong. To ensure this, the leather is sliced down a bit thinner and is coated with a polymer – which looks like a grain leather.
Suede leather: The split leather is processed further and textured to get a napped finish (soft finish). Its softness and pliability make it useful for some applications.
Suede leather looks similar to nubuck leather as it has smooth nap finish – but nubuck leather is a much stronger and durable leather. The texture of it looks similar to Suede leather.
Bonded leather: It is the lowest grade of leather; which means, not a real leather. It is rather a reconstituted leather – made by assembling bits and scraps of shredded leather with a filler and then backing them with an embossed polyurethane coating. It is cheap and not so durable as it disintegrates easily. The leather is also referred to as blended or reconstituted leather. It is used in low-grade furniture lining, sofa sets and other accessories.
Leather Tanning
Leather should not be confused with a raw skin of animal or animal hide. It is rather a processed material formed after tanning animal hide (cattle, goat, buffalo, cow) in tanneries. There are several parameters and factors that define the type of leather produced including – the source of raw material (animal hide), the type of tanning, processing of tanning and the final finishing process. Tanning process is centuries old. It has been evolving over the years and now the complete process has become automated by using machines.
What is leather tanning?
Leather is not the raw skin of animal as it is considered by many people. It is rather a processed material obtained after tanning animal skin in tanneries. The source of raw material, the type of tanning and the finishing process – all define the quality and classification of leather.
The process by which raw animal hide or skin is converted into leather to turn it into a durable and stable material to prevent decomposition is known as tanning. The agents that are used in tanning include salts, plants’ products like tannin, animal and fish oils and salts of chromium. Thus animal-based, plant-based and mineral products can be used for tanning. Tanned leather is used for a variety of leather products such as handbags, purses, wallets, shoes, gloves, upholstery, briefcases and jackets.
Types of leather tanning
The initial stages of tanning involve submerging animal skin or hide in water to soften and clean it and then curing it with salt. This process by reducing water & moisture content discourages bacterial growth and protects the hide from deterioration. Thus, the hide can be preserved for longer time.
After initial processing, the cured hide is further soaked in water to remove excess salt. Next, the hide is treated with milk of lime (liming process), which removes unwanted materials, keratins and other proteins from the hide. Furthermore, the hide is subjected to additional treatments to ensure optimal PH of the collagen for the completion of tanning process.
Different types of tanning processes that are employed to produce several types of leather include the following:
Vegetable tanning: In this type of tanning process, plant-based materials such as bark, roots, leaves and fruits can be used to make vegetable tannins that help in the production of naturally smooth, flexible and supple leather. Acacia, mangrove, chestnut and oak tree barks are used in vegetable tanning process.
Aldehyde Tanning: Leather processed by aldehyde tanning process is chrome-free. It is basically used in products that require sensitive type of tanning approach as it may be used by infants and children. Leather tanned by this type of tanning process looks more natural and has creamy colour – owing to which it is often referred to as wet white leather.
Chrome tanning: This type of tanning process involves treating leather with chromium sulphate to make raw hide into leather. The hide tanned and made into leather by this process appear quite distinct with blue colour – owing to which, leather produced by this method is known as wet blue leather. Chrome tanning takes less time than vegetable tanning and produces leather which is soft, smooth, flexible and supple and it is reasonably good for ladies’ handbags, purses, bags, jackets and clothes.
According to the required and desired features of the final leather and its products, several types of tanning methods may be employed including the usage of aluminium salts and formaldehyde.
