Natural Leather – What Is It?

According to the British standard BS 2780, the term "leather" refers to a material derived from animal hides. It retains the fiber structure almost unchanged. The hair or wool is either removed or left on the surface. Leather is known for its durability and strength and has a wide range of applications. The production of this material is one of the oldest human crafts. There are several classifications of both leather itself and the products made from it. If the material has a coating, its thickness should not exceed 0.15 mm. Leather is most commonly produced from the hides of cattle, goats, and pigs. The properties of leather vary depending on the grade. The manufacturing process of leather is quite complex and consists of multiple stages.

The general production process includes four key stages:

• Soaking and liming. The purpose of soaking is to rehydrate the hide, remove any remaining lymph and preservatives, and restore its original structure. After that, the raw material undergoes liming, where it is treated with sodium sulfide. This process loosens the structure of the dermis and modifies the collagen fibers.
• Tanning and retanning. This is a chemical process that transforms raw hides into finished leather. At this stage, acids and tanning agents are used to dissolve fats, break down the chemical bonds of collagen fibers, and remove non-fibrous proteins.
• Finishing. This stage includes dyeing and further processing of the leather.

A hide that has not undergone tanning is not yet considered leather, as its collagen proteins remain weak and are not resistant to moisture and heat. There are numerous tanning methods, but the most popular in the leather industry is chrome tanning. This method, invented in 1858, involves treating semi-processed hides (wet-blue) with chromium salts.