What tanning processes are there?

Tanning is an important part of transforming raw hides into the leather items we use on a daily basis. Through the years tanning as a process has changed to comply with the demands of our society and industrial changes. There’s a lot of diversity in the various tanning processes and there are pro’s and con’s to each of them. To be able to explain the most used tanning processes, we first have to explain what the actual process of tanning is and its purpose.

What is tanning?
The purpose of tanning is to turn a hide into a crust. This is then finished and turned into the   material we use for furniture, clothing and various other applications. The process of turning hides into leather can be divided into four phases. Firstly the raw material is transported from mostly meat and dairy companies, as most leather we use is a byproduct from these industries. Secondly, the raw hides are prepared for the tanning process in what we call the beamhouse treatment. Beamhouse is a historic term, referring to curved surfaces, referred to as beams, where upon hides would be dried. 

Now the skins are ready for the tanning process. The purpose of tanning is to make the leather usable and increase its lifespan. Simply said, without tanning leather would not be able to last for years and simply decompose. The word tanning is derived from tannin, which is historically one of the substances used in this process. The skins would be treated with tannin (and various other substances), to stabilized the protein structure of the skins.. The various methods of tanning are defined by their use of different chemicals. Each method has different results, advantages and disadvantages. 

Natural tanning
Though it sounds like tanning is a particular process of human intervention, tanning of skins does happen naturally. For instance, there is bog tanning. These are animals that ended up in swamps, where their skins have been preserved for centuries. The chemicals present in the bogs take care of preserving the skin. Some of these skins, which we can still find in our natural history museums, are thousands of years old. This is the oldest known form of tanning and has inspired our ancestors to look for ways to preserve hides using similar processes.

Vegetable tanning 
To emulate this process, but obviously not willing to wait for years and years, manufacturers need other methods. Our ancestors started to tan skins with natural acids, like tannin, cedar oil and alum. The current process of vegetable tanning we use nowadays is pretty similar to what it was in the past, though production has been optimized. Tannins used are derived from tree bark or other natural resources, which results in natural looking leather with a sturdy look and feel. This sort of leather is suitable for suitcases, belts and furniture and is often viewed as a more sustainable method of tanning, due to his natural resources. However, vegetable tanning is a very time consuming process with a high use of energy and resources. Due to the high global demand, the application of this method is therefore limited. Vegetable tanning would need vast amounts of resources, which would indirectly impact forests.

Chrome/Blue tanning 
The process of tanning remained pretty much the same up until the 19th century. Higher demand and new chemical innovations introduced chrome tanning. This new chemical process was invented to improve how efficient and reliable the tanning process would be. The use of chromium enabled the tanning industry to push out larger volumes, which met the requirements of the time. In particular during wartime, the need for leather was enormous. This need also turned out to be an engine for further improvements in chrome tanning. The name is derived from the use of chromium sulphate, which is part of the chemical mix that makes chrome tanning so effective. This method has also been dubbed ‘wet blue’ or ‘blue tanning’, because of the blue hue leather has after treatment. Chrome tanning has been a focus of criticism on the tanning industry, due to the perception of it not being as sustainable as alternative methods. Chrome tanning is the most used tanning method due to its fast and efficient process, which has become vastly more sustainable thanks to chemical innovation.

Our own Stahl EasyBlue Tan™ is a system, which makes the process more sustainable due to reduction of wastewater, lowering the amount of chrome and salt needed, while still maintaining high-quality tanned leather. 

Glutaraladehyde/White tanning 
The demand for alternatives to chrome tanning has prompted new methods that avoid heavy metals like chromium. . The white taint left on the wet leather is why it’s also known as ‘wet white’ or ‘white tanning’. The process for glutaraldehyde tanning is not dissimilar to chrome tanning, and need also the addition of salt and acids. The process is considered to be more complex.

White tanning is considered a more environmental-friendly alternative to blue tanning. This mostly is due to its general labeling as an alternative that is more sustainable. Like other methods, white tanning is a process that keeps seeing new innovations. 

One of those innovations is our Stahl EasyWhite Tan™ system, which allows for the process to be simplified and thus more efficient. The advantage is a further reduction in wastewater, the use of chemicals and salt. The resulting leather is a durable product of high-quality. 

Tanning and sustainability
Looking more closely at the three methods, it’s hard to say which one would be the most suitable. All of them have their advantages and disadvantages. You can compare the different tanning methods by their use of salt, chemicals, energy and water, the personnel costs or complexity of the process. Another side tot his comparison is the resulting durability and quality of the leather. At the bottom line, due to that complexity it’s hard to determine which process would suit a leather manufacturer the most. Apart from the factors mentioned earlier in this paragraph, it also depends on the needs and requirements that manufacturers OEM’s and brands have when using leather in their collection. 
All in all it is hard to reach a consensus on which tanning method is best, but there is consensus on where the industry is going, and that is towards more sustainable production methods. This is the common goal of the entire leather industry and step by step, we will contribute to make these processes better, more sustainable and more efficient. 
Do you have questions regarding this topic: please don't hesitate to contact us