Ledergerbung
How does a tanning process for leather goods work
Ledergerbung: Wie funktioniert ein Gerbverfahren für Lederwaren
Leather tanning is the crucial step in leather production, preserving raw, perishable animal hides, transforming them into durable leather, and giving them flexibility and a pleasant feel. There are various processes for this transformation. These include so-called "true tanning," which encompasses vegetable leather tanning and chrome tanning. Alum tanning and oil tanning, for example, are classified as "false tanning."
A leather manufacturer usually purchases already tanned leather hides for further processing. The raw material, the animal hide, is initially a perishable, organic product. Only through processing does the raw material become a resistant and durable end product that can be made into a leather bag, shoes, or a leather sofa. This transformation requires an elaborate processing procedure that – depending on the type of leather and tanning method – takes several weeks to months.
WHAT HAPPENS DURING LEATHER TANNING?
The most common tanning methods are chrome tanning and vegetable leather tanning, which are often combined with each other or with so-called synthetic leather tanning.
During tanning, the animal hide is transformed into more durable and less perishable rawhide through the addition of various process chemicals. The tanned leather is then processed in the later manufacturing process, for example, in the clothing or automotive industries.
The main tanning process primarily makes the leather durable. Other desirable characteristics, such as particular softness, dyeability, and grain tightness, are added to the already tanned leather through retanning.
WHAT TYPES OF TANNING ARE THERE?
There is a variety of tanning processes, some of which are very old. Not all are suitable for industrial use. The most important types of tanning can be broadly divided into "true tanning" and "pseudo tanning".
"TRUE TANNING":
During tanning, the skin fibers and tannins form an irreversible, i.e., permanent bond. True tanning makes the leather particularly durable.
Mineral tanning, especially chrome tanning
75 - 80% of the world's leather is chrome-tanned. German and European tanneries generally operate under strict regulations and can guarantee a quality of chrome-tanned leather that is harmless to health.
Vegetable/plant-based leather tanning
Here, the leather is tanned with oak or spruce bark, quebracho wood, tara pods, olive leaves, rhubarb roots, or mimosa bark. If you value sustainability, you should also pay attention to the origin of the tanning agents, because vegetable tanning is not always truly more sustainable than chrome tanning!
Synthetic leather tanning
Synthetic tanning agents are artificially produced and mostly used in combination with mineral or vegetable tanning. Leather tanned exclusively with synthetic agents is very sensitive to moisture, heat, and UV radiation.
"IMPERMANENT TANNING":
With these tanning methods, an unstable bond forms between the leather and the tanning agents, which can be easily disrupted by environmental factors such as heat or moisture.
alum tanning
Dyeing with aluminum salts results in a whitish, very delicate leather.
tanning
Tanning leather with fish oil is considered the oldest known tanning process. During a production period of three to four months, the oxidation of the oil results in leather with a yellowish color.
WHICH TANNING METHOD IS THE MOST COMMON AND WHY?
Chrome tanning remains the most common and time-saving method for tanning leather and, according to Andreas Meyer, managing director of the Association of the German Leather Industry (Verband der Deutschen Lederindustrie e.V.), it is not as bad as its reputation suggests.
"Many people are afraid of chrome-tanned leather because it is said to be harmful to our health," he explains, "but in fact, there are no statistics to support this."
Although chromium-6 in liquid and gaseous form is highly toxic and should never be inhaled or swallowed, through proper processing with appropriate reducing agents, which exclusively takes place in German tanneries, it is converted into chromium-3. "Anyone who reacts sensitively to leather treated in German tanneries either has a chromium or a leather allergy," says Meyer. However, he states that the leather is certainly harmless to health.
WHICH TANNING METHOD IS THE MOST ENVIRONMENTALLY FRIENDLY?
While vegetable leather tanning does not use chemicals, chrome tanning is much more effective and time-saving than vegetable tanning. "Therefore, chrome tanning, contrary to its reputation, is in some cases even more environmentally friendly than vegetable tanning," Andreas Meyer points out. According to the expert, the much more elaborate vegetable leather tanning consumes a lot of energy, and in order to achieve the leather properties desired by consumers, such as a soft feel and UV resistance, chrome often has to be used in the retanning at the end. "German tanneries now work with such good wastewater technology that chrome tanning can certainly hold a candle to vegetable tanning in terms of sustainability," says Meyer.
WHERE DO THE HIDES PROCESSED IN GERMAN TANNERIES COME FROM?
Not only the tanning processes, but also the origin of the hides that are processed into tanned leather play a role. A large proportion of the hides processed by German tanners are of European origin. According to Meyer, Southern European bull hides are particularly suitable for processing in the furniture or automotive industry due to their large size. North German bull hides are popular for accessories and the clothing industry. "With our German companies, traceability to the slaughterhouse can always be guaranteed," promises Andreas Meyer. This means you always know exactly where the processed animal hide comes from. This is, of course, not always the case with foreign companies.
Anyone who values sustainability, fair working conditions, animal welfare and quality will receive leather tanned to high standards from German tanners, which meets our health standards and our demands for high quality and durability.
HOW MANY TANNERS ARE LEFT IN GERMANY?
"The profession of tanner has a disreputable reputation in this country," regrets Andreas Meyer, "most young people prefer to sit behind a desk."
But it is a craft rich in tradition that is often passed down within the family. What is striking is that there are few dropouts. "Once you start tanning, you never stop," laughs Meyer, "that's saying something!"
In Germany, the tanning process is subject to strict regulations that protect animals and humans and ensure the quality of the leather. "These regulations are important," explains Meyer, "but meeting them has become almost impossible for smaller (family) companies." This is why tanners often join together to form larger associations. Today, there are still around twelve larger tanneries in Germany with over 50 employees. In order to produce more cheaply, many companies have their leather tanned abroad. However, German tanners can usually guarantee better quality and environmental standards. This is why it is worth investing in leather products that have been tanned in Germany or Europe.
