With the growing desire to use sustainable products that are safe for the environment, manufacturers and consumers alike are taking a closer look at how leather is made and the harmful effects the tanning industry might have on air and water quality.
There is much discussion, as well as confusion, about the differences between chromium and vegetable-tanned leather, as well as the benefits and drawbacks of each.
The popular belief is that vegetable-tanned leather is preferable because it is made “naturally” and will biodegrade at the end of its useful life, whereas chromium-tanned leather is often frowned upon because of the use of heavy metals to produce it and the fact that it is it cannot be destroyed, remaining in landfills indefinitely.
In this article, we delve into the difference between chromium-tanned and vegetable-tanned leather, as well as their pros and cons.
What Is Tanning?
Leather is an organic material that will decay in its natural state. Tanning is the process used to preserve leather hides or skins, making them resistant to degradation. Its purpose is to prevent putrefaction without compromising the leather’s softness, flexibility, and original fibrous structure. The process works by modifying the leather’s collagen, a protein that is one of the main building blocks of skin, making up 75% of the skin’s support structure.
Tanning is achieved by saturating the hides with tannins, molecules that easily bond with proteins and draw out the liquid. There are many ways to tan leather, with some techniques dating back thousands of years. The two most commonly-used tanning solutions are vegetable tannins and mineral tannins. Chromium sulfate solution (“chrome”) is the most popular mineral tannin.
Tanneries choose to use a particular tanning method based on the ultimate use of the leather. For example, if the leather needs to be soft and supple for making garments or furniture, typically it is chromium tanned, whereas vegetable-tanned leather is most commonly used for shoe soles, wallets, belts, and saddlery.
Vegetable tanning is an ancient craft, first used more than 6000 years ago in the Middle East. Chromium tanning, on the other hand, was invented in the mid-1800s to speed up the leather-making process while making it less costly. It quickly became the basis for the development of leather-making on an industrial scale.
As much as 90% of leather produced in the world is tanned using chromium compounds. While vegetable-tanned leather is associated with tradition and craftsmanship, only a minority of modern tanneries have the equipment or capacity to make it. Because time and skill are required to produce vegetable-tanned leather, it is also expensive, particularly compared to its chromium-tanned counterpart.
How Is Vegetable Tanned Leather Made?
Vegetable tanning is an organic method that has changed little since it was used by ancient people. It relies on natural vegetable tannins to preserve, strengthen and color the leather.
The tannins are derived from the bark of oak, chestnut, and mimosa trees, although other types of trees are also used. The process is complex and lengthy, taking as long as two months and involving the dedicated work of highly-skilled craftsmen.
The process begins by soaking dehaired leather hides in a solution of vegetable tannins. Traditionally, the tanning was accomplished by suspending the hides in pits. Today, the hides are hung from racks in vats containing the tanning solutions. They are moved from vat to vat, each with progressively stronger solutions.
At the end of the process, the hides are left to soak. The result is a material that is thicker and stiffer than chromium-tanned leather, making it suitable for accessories such as wallets and belts, as well as suitcases, shoe soles, and saddlery. Vegetable-tanned leather is not suitable for applications that require the leather to be thinner and more flexible, such as upholstery and garments.
The Advantages of Vegetable Tanning
Vegetable-tanned leathers have a unique, natural beauty, with a reputation for improving with age. The leather is saturated with the wood colors of the tanning solution that deepen into a beautiful patina over time.
This type of leather continues to be associated with heritage, tradition, and craft. It is sturdy and durable, lasting for decades. Vegetable tanning is a natural process, using just tree tannins and water, resulting in leather that is biodegradable. It has an “earthy” smell and feels more organic and alive.
The Disadvantages of Vegetable Tanning
Although seen as an “eco-friendly” solution to leather-making, vegetable-tanned leather does have its drawbacks:
- Made by very few tanneries
- The process is lengthy
- Expensive to produce
- Too thick and stiff to be used for many applications, such as upholstery
- Does not absorb color well, resulting in limited color choices
- Not as fade, stain, and abrasion resistant as chromium-tanned leathers
- The tanning process requires more use of water and tanning agents
How is Chromium Tanned Leather Made?
Chromium tanning was developed in the nineteenth century to serve three purposes: to speed up the tanning process, to render the hides more flexible and supple, and to prepare them to accept color uniformly.
This type of tannage is carried out by using chromium sulfate, a mineral salt that penetrates the hide rapidly, completing the process in a day or two. The hides are tumbled in huge rotating drums (large enough to hold more than 100 hides) partly filled with a chrome salt solution. The leather is then cleaned, dried, and smoothed in preparation for bleaching and dyeing.
Chrome tannage is resistant to the effects of harmful air pollutants. It also yields strong, inherently soft leather that is thinner than vegetable-tanned leather. It is appropriate for furniture upholstery, clothing, and gloves.
The Advantages of Chromium Tanning
In addition to being efficient and cost-effective, chromium tanning results in a thinner leather that has high stability, softness, mechanical flexibility, and good dyeability and color fastness. It can be dyed into an unlimited array of hues, making it ideal for the fashion industry, in which color trends can change quickly.
The Advantages of Chromium Tanning
Chromium-tanned leather is often viewed unfavorably because of its reputation for being harmful to the environment. There are other disadvantages as well:
- The use of heavy metals can have a negative environmental impact
- Not biodegradable and cannot be recycled
- Can have a negative effect on workers’ health
- Can cause off-gassing
What Is Your Leather Made From?
The tanning process used is based on the ultimate function and desired look of the leather being produced.
Chances are that your leather accessories are made from vegetable-tanned leather, which is thick and rigid, while your sofa and jacket are produced with leather that has been chromium-tanned for softness, thinness, and pliability. Here at Kovi Fabrics, our leathers are made for upholstery and are, therefore, chromium-tanned. Click here to see our fine collection of over 300 colors and qualities.
Look for future articles on alternates to chromium-tanned leather and the newest technology to make chromium-tanned leather kinder to the environment.