Leather is one luxurious material that goes through various refining processes, and tanning is one treatment for hides that prevents rotting and putrefaction of the leather. The different types of leather offer unique characteristics, which are further influenced by the method of tanning they go through. This inspires to know how many types of leather tanning are there, and what method seems best?
From vegetable tanning to chrome tanning, there are different tanning methods employed by leather tanners. And all these refining techniques have various merits and drawbacks while tackling a common issue – removing moisture from the hide’s collagen.
Have you ever wondered what steps are involved in refining raw leather hides? Not to worry, this article covers all you should know about leather tanning processes.
Different Types of Leather Tanning
Once leather hides are sourced, they are subjected to certain pre-treatments. These treatments often involve salting and liming – this helps preserve the animal skin before it gets to the tannery. Then, the next step is tanning, which is done in different steps.
So, what does it mean to tan leather? Leather tanning is a procedure that completely alters the hide’s protein structure while making it less susceptible to rotting and decomposition.
You should know that leather dates back to prehistoric times, employed for making various items. In such ancient times, animal skin was preserved through various means, with some curing methods quite effective and others not sustainable.
Nevertheless, tanning has come a long way, and you can now find various tanning routines with specific improvements. While there are various leather tanning methods, you would find most tanners choosing a type of tanning based on what they need for their final product’s appearance.
To understand the leather material’s uniqueness, it is crucial to learn about the different tanning methods. Hence, you should know that there are four types of skin tanning for leather and these widely familiar methods include:
- Vegetable tanning
- Chrome tanning
- Chrome-free tanning
- Zeolite-based tanning
Vegetable Tanning
Vegetable tanning of leather refers to a traditional tanning method that employs tannin-rich plant extracts derived chiefly from tree bark, trunks, and leaves. What’s more, tanners blend the tannin extract according to the choice of strength, feel, and color needed in the final product.
Some plants employed for this purpose include Mangrove, Chestnut, Oak, Hemlock, Redoul, Wattle, and Quebracho. The more the hide absorbs the tanning solution, the more its physical properties change.
This type of tanning method is the oldest and one of the most environmentally-friendly option you can find. Vegetable tanning dates back more than 5000 years ago, traced to the Ancient Egyptians.
For thousands of years, the Romans controlled and regulated the industry, and the orthodox recipes have been concurrently modified. Modern vegetable tanning now uses avant-garde technologies.
However, the three significant steps involved in vegetable tanning are explained below.
- The pre-treated and de-haired leather hide is soaked in a vat or tub filled with the tannin extract blend.
- For an excellent result, the hide is left to soak for at least 1-2 months.
- Then, the leather is removed and oiled, waxed, or hot-stuffed to increase its durability and suppleness.
Vegetable-tanned leather is strong, durable, and helpful in making leather clothing, footwear, and furniture. It also has unique earthy colors, which are pretty attractive. Nevertheless, leather experts sometimes subject the veg-tanned leather to “fatliquoring,” a process where they dye and grease the hide and even get it retanned.
The main downside to vegetable tanning is its long processing time, which also influences its cost in the market as you can find veg tan leather products very expensive.
Chrome Tanning
Chrome tanning is another famous method used to cure more than 80% of leather items worldwide. Chrome-tanned leather is soft, supple, and reasonably resistant to scratches, stains, and moisture.
That type of tanning contributes to further improving the quality of leather. Kindly, note that chrome tanning uses mineral salts (trivalent chromium) instead of natural tannins. To testify unfailing effectiveness chrome-tanning one must know that this tanning procedure dates back to the late 1800s, invented to assist with mass leather production.
Undoubtedly, chrome tanning is effective and swift, as it can get completed within a day. Although the adverse environmental impact of the wastes from chrome tanning raises a significant concern, some measures are now taken to tackle such problems.
Hence, the tanning process keeps getting overhauled, and better waste management procedures are introduced. With that in mind, these are the basic steps in chrome tanning.
- Chrome tanners get the pre-treated leather
- Then, a solution of the chemicals or salt is filled in different types of leather tanning drums, baths, or tubs at the tannery.
- The pre-treated leather hides are now immersed in the baths/tubs and left for about 24 hours.
- The chrome-tanned hides are removed and left to dry.
You can take a step further to dye the leather using various colorants, and the dye penetration occurs quickly due to the uniform properties of this leather type. To also make the dye last longer, you should seal the leather.
Chrome-Free Tanning
Chrome-free tanning has kept gaining a certain level of dominance within the industry. Chrome-free tanned leather is often maintained to meet specific requirements and finds excellent use in automotive applications.
The most famous of this skin tanning method for leather is aldehyde tanning, which employs a glutaraldehyde solution. Compared to chrome tanning, chrome-free tanning has a more complex procedure.
Unless a standard temperature is reached, the chrome tanning will not occur successfully. Also, such leather would need more chemicals for specific post-tanning improvements.
So, before the tanned leather gets discharged and employed for manufacturing products, it undergoes further treatments to enhance its properties. You can tell chrome-free tan products from others as they come with a “FOC” tag, which indicates “free or chrome.”
Zeolite-Based Tanning
Zeology is a novel and innovative tanning concept that appears to be a sustainable option. The zeolite chemicals have a characteristic property that absorbs and liberates moisture as the temperature fluctuates.
These zeolites are made of renewable and natural components abundantly found within the earth’s crust. Impressively, subjecting leather to this form of treatment does not compromise its performance. Moreover, this type of tannage supports the absorption of water without letting the hide swell, which is one desirable characteristic.
Frequently Asked Questions (FAQs)
Q: What are the types of tanning methods?
The different leather tanning methods include vegetable tanning, chrome tanning, chrome-free/aldehyde tanning, and zeolite-based tanning. These varying tannage options follow similar steps while subjecting leather to different tanning agents. However, the first two are the predominant tanning procedures in the industry.
Vegetable tanning, the oldest option, uses tannin-rich extracts from mainly the bark, leaves, and trunks of trees. Since vegetable tanning appears time-consuming (it takes at least two months to finish), chrome tanning was developed for mass leather production; this leather tanning uses chromium salts.
Q: How can you tell if the leather is chrome or vegetable tan?
Two significant tests can help you tell chrome-tanned leather apart from vegetable-tanned leather. The first test requires you to burn a strip of leather using a lighter. Leather that goes through chrome tanning burns faster, with much ease, and leaves behind green ashes.
If, however, the leather takes longer to burn and leaves behind grey or black ashes, it is vegetable-tanned. On the other hand, the second test involves introducing a strip of leather into a bowl of boiling water. Chrome-tanned leather generally floats on boiling water, whereas vegetable-tanned leather starts curling once introduced to hot water.
Q: How many types of tan are there?
Regarding leather tan, there are two primary options; vegetable tanning and chrome tanning. Vegetable tan often takes the hide through a tannage process that employs plant extracts rich in tannings. However, chrome tanning makes use of chromium in curing the hide.
Other standard tanning options include chrome-free/ aldehyde tanning and zeolite-based tanning. Each tanning process gives the leather its characteristic color, feel thickness, and more.
Q: What tanning method is best for leather?
The best way to tan leather depends on your needs and the characteristics you want the final leather product to possess. Different types of leather tanning have their pros and likely cons and further influence the leather’s properties.
So, while vegetable tanning would give thick, durable, and strong leather with a natural color, the process is time-conditioning, and the leather may not be suitable for specific applications. Similarly, you may find chemical and mineral tanning effective and less-time conditioning, with such leather emerging very supple, but it may also not be the best for some applications.
Q: What are the stages of tanning?
Leather tanning occurs in six major stages:
- Getting the Hides: Here, the hide, a byproduct from animals, is sourced from slaughterhouses using a metal tool or machine.
- Pre-Tanning Treatment: The pre-treatment of the hide usually involves salting to preserve the leather as it gets transported to the tannery and liming to help remove the hairs and fats on the animal skin. In this stage, the hides also get split into different layers.
- Proper Tanning: At this point, the pre-treated hide is placed in a bath filled with tanning agents based on the chosen method.
- Drying and Selecting: The excess moisture is removed from the tanned hides, and the leather is further graded based on the location, quantity, and natural markings.
- Dressing and Finishing: Now, the leather is shaved to have a uniform thickness and sealed to prevent likely damage from exposure to moisture and other environmental conditions.
In addition to the leather tanning and finishing process, you can also decide to dye, grease, and re-tan the leather.
Q: Why does leather get hard after tanning?
The hides of animals have a colloidal nature; hence, they readily coagulate when subjected to various tanning agents and get hardened. Kindly, note that leather hides have positively charged particles, and the particles in the tanning agents, like tannin, are negatively charged, which allows such coagulation.
Nevertheless, some leather still emerges softer than others, and you can also harden leather with specific procedures to toughen up your leather piece.
Q: Does vegetable-tanned leather scratch?
Vegetable-tanned leather is not resistant to scratches; hence, exposing them to even the slightest harsh conditions is not advisable. Nevertheless, you can easily buff minor scratch marks using a soft-bristled brush or microfiber cloth. Conditioning the leather would also help conceal such imperfections.
Q: Does chrome-tanned leather crack?
Chrome-tanned leather tends to crack after some time, which is a significant downside of this tanning process. During chrome tanning, the leather hides absorb the solution quickly, disintegrating the hide’s properties. Thus, while you find chrome-tanned leather soft and supple, you may start noticing the leather craft peeling or cracking.
Final Words
As a unique material, leather undergoes a refining or curing process that helps preserve and make it suitable for manufacturing long-lasting products. Leather tanning actively removes moisture from the collagen of the animal skin and prevents the active growth of microbes that could cause rotting.
There are varying tanning techniques, and all tanning methods get appropriately managed. And all these variables give superior leather materials with properties, resulting into a refined final product. This article offers you an in-depth exposure to the various types of leather tanning to help you make a better choice of the kind of leather you need for your crafts.
