Leather production – how leather is made

Ad| Leather builds the basis amongst others for handbags and small leather goods. Choosing the right leather will have a big influence on the life-cycle of a leather product and thereby an impact on the designer and the label it is being branded with. The more it is important to know about its origin and about the process of the leather production. The majority of the leather is made in China, followed by Italy and India. Leather is a by-product of the meat-industry.

The leather production process

The modern leather production process in a tannery starts right at the moment when the hides arrive. Before, hides used to be salted and stored till they were processed. Today every cost of a storage space should be avoided. The modern tanneries tend to start off from fresh (but chilled) hides, coming right from the slaughterhouse. In this way also two steps in the production can be saved (salting and washing the salt off again) and the leather production can start immediately. In order to turn a hide into leather, more than 50 working steps a required. The basic ones will be described in the following:

Beamhouse

• In drums, the hides will be cleaned from salt, blood, meat rests and dirt. By adding certain supplements to the water, the hides or skins will come back to its original state. Hair and certain proteins will be removed from the skin in the next process, the liming.
• Due to the chemicals used in that process, the pH-value in the water will rise tremendously, the pores will open up and the skin will swell to double its size. In this way two pieces can be made out of one by splitting. The upper part is called grain skin and contains the epidermis or grain layer. The lower part, the split skin, is either used for further (split-)leather production or sold to some other industries, e.g. the food or glue industry.
• The skins come back into the drum and will finally be prepared for tanning – natural fats will be segregated, the rest of the dark skin pigments will be removed through scrubbing by a process called bating and the collagen in the hides will be prepared by opening up to receive the tanning solution in the best way: vegetal based, synthetic based or with minerals.

Tanning

• Before starting the tanning process, you have to decide about the quality of the leather: should it be soft, hard, thick, thin and which colour should be achieved?
• Due to this decision, tanning supplements have to be added in order to convert the hides into stable leather. There are different possibilities with their own particular advantages like vegetable tanning, chrome tanning or tanning with minerals or other (metal based) chemicals. They all need to be added to the hides in a certain way in order to connect with the collagen structure of the hides.
• After that process the leather can be shaved delicately to the final thickness, the water will be pressed off, and the retanning process with dying and fatliquoring starts.
• In the following mechanical processes the leather will be flattened and the water will be stretched out again in order to soften the leather and to dry it properly. Now we call the tanned, dyed and fat-liquored leather: crust.

Finishing

• The final step of the leather production will then be the finishing.
• Defects, such as scratches or damaged grains will be treated and base coats will be applied on the surface.
• If the leather should have a certain surface with a certain structure, it can be embossed in the leather at that stage.
• Finally the topcoat will be adjusted to the surface to get the desired finishing for the final leather product. The desired properties will be achieved by using the right base- and topcoats.

Testing

In order to proof, if the leather is stable and keeps its color, various test like

• adhesion
• flexes
• rubs
• water resistance and
• tear strength tests

should be made. But therefore every brand has ist own requirements.

A detailed overview over the single phases of the leather production process provides you the graphic from Stahl.

If you want to learn more about the leather production, e.g. which products you can use to tan more environmentally-friendly, how to make your own leather finishing or even which process you need to start in order to get e.g. soft leather or long-lasting colours, Stahl Campus Manager Frans van den Heuvel can help you.

In order to achieve a more and more sustainable supply chain within the leather industry, together with Stahl, he initialized the knowledge center Stahl Campus 2014 in Waalwijk, the Netherlands. Here, Stahl invites brands, tanners, manufacturers and others to workshops in order to strengthen their knowledge of the leather production.

More about Stahl Campus and contact information you will find on the website.

Details about my visit at Stahl you can read here.

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