What goes into making leather

Manufacture of leather

Leather is made from animal hides. There are differences in the individual processes, depending on whether the approach is chemical or natural and whether the work is done traditionally or mechanically. In total, a number of individual steps are carried out. The tanning is the best known and most important individual process.

Individual steps in leather production

The most common individual steps, as they occur in chrome tanning, are briefly presented here.


1. Raw skin

2. Measure and select

3. Switches

4. Ashing / depilation

5. Defeat

6. Columns

7. Pickling

8. Descaling

9. Pimples

10. Tanning

11. Neutralize

12. Wilting / draining

13. Retanning

14. Sort

15. Folding / thickness regulation

16. Wet finishing

bleaching

To dye

Grease / leak

17. Softening (Stollen, Millen, Walken)

18. Drying

Hang drying

Vacuum drying

Stretch drying

Pasting process

High frequency drying

19. Surface treatment

1. Rawhide

At the beginning of the leather production process there is the raw hide, which is completely untreated. If a rawhide cannot be processed into leather immediately after extraction, it must be stored. This is only possible if the skin is preserved, as bacteria start to decompose the skin within a very short time.

2. Measure and select

At the beginning of leather processing there is always an inspection of the raw material. The dimensions of the hides are usually taken by hand, but also by machine. Thicknesses are determined, possibly even tightness and strength checked. In each case, the skins are also examined for blemishes.

A control of this kind is necessary again and again in the entire manufacturing process so that the end product meets all requirements for further processing.



3. Switches

After the hides have been stored, they must then be returned to their original state. This starts with the skins being soaked.

4. Ashing / depilation

The aim of liming is to remove the superfluous hairs from the skin and to reduce the amount of fat. Of course, this step is only necessary if the skin is to be used without hair. This step is accordingly omitted for furs and hides.

This makes liming an important step in preparation for the most famous tanning step. In the past, as the name suggests, this procedure was carried out using ashes. Today calcium hydroxide and sodium sulfide are often used for this purpose. However, these substances generate wastewater, which then has to be treated and must not enter the environment.

Liming is the work step that has a decisive influence on the properties of the later leather. The longer the hides stay in the liming, the softer the leather becomes. So if firm, robust leather is to be produced, the liming time is shortened.

After liming, the hair of the epidermis is loosened, meat and fat residues loose enough to be removed and freed from unnecessary proteins and fatty substances. The hide is further prepared for tanning by swelling the leather fibers and opening up the hide.

The hair has now been loosened by the liming so that the hides are completely removed in the step of depilation.


5. Defeat

As already described, the skin is already prepared for the meat removal.

6. Columns

A skin is made up of different layers called crevices. In the splitting step, the skins are separated into flatter columns. It is common to separate the flesh gap, grain gap and central gap.

7. Pickling

Staining makes the leather softer and the fibers in the leather more flexible. In this work step, enzymes are used that break down various proteins.

8. Descaling

This work step is also called descaling and is already explained in detail by the name.

9. Pimples

Acid and salt lower the pH of the skins and make the skin receptive to the tannin.

10. Tanning

Tanning is the term that describes the actual change from the hide to leather. So far, there was a skin that contained native proteins and was therefore still an organic, rapidly decomposing material. The tanning now fixes and cross-links the proteins, so that stabilization takes place, which makes the leather less susceptible.

The actual tanning process takes place in the widespread chrome tanning by adding chrome salt (III-valued). In other tannins, a wide variety of other substances are used, which can be natural, synthetic or chemical.

11. Neutralize

During the neutralization, the skins are adjusted to the following steps in terms of pH.

12. Wilting / draining

The aim of withering is to free the skins from the water. To do this, the skins are pressed between two rollers.

13. Retanning

Retanning refers to the process that subjects the hide to another tanning process. The aim is to optimize the hides, especially in terms of appearance and feel. Depending on the later use, the hides can be made ready for special dressings during retanning. For example, the softness, the visibility of the grain structure, the lightfastness, the coloring, the weight, the stability and the dyeability can be influenced.

14. Sort

The seemingly simple step of sorting the skins is similar to the first step described here, a step that has to be repeated over and over and is very significant. The hides are checked for cracks, size, grain defects, firmness, parasite infestation, etc. The leather can then be sorted according to quality.

15. Folding / thickness regulation

If, after the inspection, the hides do not meet the requirements in terms of thickness or are uneven, they are planed smooth by being fed into a machine designed for this purpose. The scraps of leather that have been peeled off are often put together and resold as inexpensive upholstery leather.

16. Wet finishing

The steps of bleaching, dyeing and greasing are considered wet finishing.

bleaching

When the leather is bleached, unwanted discolorations or uneven colors are adjusted.

To dye

The leather can then be dyed in the desired color. Depending on the method, it is possible to dye with natural or chemical agents.

Grease / leak

The greasing of leather is used as a way of making the leather softer.

17. Softening (Stollen, Millen, Walken)

18. Drying

Hang drying

Vacuum drying

Stretch drying

Pasting process

High frequency drying

19. Surface treatments

As an example, the leather extraction can be shown in a photo series, as it is similar to our Gusti leather studio products.

Additional sources: https://www.leder-info.de, accessed on: 15.06.2018, https://www.leder-info.de/index.php/Gerbung, accessed on: 02.07.2018.

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