Tanning chemicals: what are the options?

What are types of leather tanning chemicals?

Of course, Zeology is all about chrome free leather tanning, but what other types of tanning chemicals are there? And what are the differences? In this article we explain and compare:

  • Chrome tanning chemicals
  • Vegetable leather tanning
  • Chrome free tanning (aldehyde)
  • Zeology tanning, the chrome free & aldehyde free method

Chrome tanning

About 75% of leather made today is chrome-tanned. The process uses trivalent chromium (Cr III), which is a safe substance. It is even an essential part of our diet! Many people take daily supplements that contain it chromium.

Unfortunately, there is a lot of misinformation about the leather industry in relation to chromium. It is sometimes suggested that hexavalent chrome, or chromium VI (Cr VI) is used for tanning leather, and that it is carcinogenic. Chromium VI is not used in the manufacturing of leather! Moreover, there are clear and effective industry guidelines set out by the Leather Working Group (LWG) to prevent its formation in leather after tanning.

The process of chrome tanning is constantly being upgraded, as its uptake is improved, less of it needs to be used, there is comprehensive recycling, reduced water consumption and careful management of waste. Best practices in chrome tanning use half the chemicals required by other traditional tanning methods, and produce effluent content below legal requirements. Chrome tanning produces consistent leathers that can be used or worn, year after year, without any loss of properties.

Vegetable tanning

Vegetable tanning is the oldest tanning method. It uses extracts from wood, and nuts of trees and shrubs. Responsible suppliers ensure these come from a sustainable source. It usually takes longer to tan leather using this method, but the result is a leather with a distinctive aesthetic and handle, which ages beautifully.

Its naming, as well as the tanning materials used, make it seem as if vegetable tanned leather is more ‘eco-friendly’. However, we need to take the entire balance across the whole process into account, to make a more meaningful comparison with other methods. For example, vegetable tanning uses a few times the amount of tannins than for chrome-tanned leathers. The effluent produced also requires more treatment before it can be discharged. However, it has the benefit of using natural, sustainable and renewable raw materials.

Chrome-free tanning chemicals

There is a number of other tanning methods, known by different labels. They are usually grouped and referred to as ‘chrome-free’. Chrome-free leathers are usually made for a specialized performance requirement, or often specified for automotive use. The most common is aldehyde tanning, which utilizes glutaraldehyde. Leathers made with this tanning agent require relatively more chemicals after tanning, to improve the leather properties. For this reason, the effluent of a glutaraldehyde based chrome-free process will require additional treatment, before it can be discharged.

Chrome-free and aldehyde-free: zeolite tanning

A new innovation in tanning chemicals is the use of zeolites. Zeolites have a unique property in that they can absorb or release water, depending on the temperature. Water absorption is an important part of leather comfort, and a tannage that allows water absorption (without swelling) is a desirable characteristic.

There are eight main groups of zeolite minerals that occur naturally. Two major types of zeolite, named zeolite A and zeolite X, are produced synthetically and widely commercialised. These synthetic versions can be modified by adding an organic acid, to produce the unique zeolites that can be used in the tanning process.

Zeology is the first and only well-performing leather tanning product that is zeolite-based. Chrome-free, aldehyde-free and heavy metal-free.

Learn more about leather tanning and Zeology:

zeolite in detail

The science and chemistry behind Zeology

An in-depth and scientific-based explanation of how Zeology and zeolite works. Watch the movie.

The tanning processes

Discover how the Zeology tanning processes work.

Leather tanning

The leather making process: step by step

How is leather made? How to source the most sustainable leather? An overview.