Gustavo Adrian Defeo is an internationally known and respected chemist/tanner. He is of Argentinian origins and has been working in Italy for years.Ê He founded the company ARS Tinctoria, located in Santa Croce sullÕArno (Pisa). Defeo is a great expert in industrial colour physics, collaborates with some multinational chemical companies and several important fashion brands. Recently, he carried out a study on the risks of metal-free tanning, which he presented during a seminar organized on behalf of AICC in the tanning districts. We asked him a few questions.

What is your opinion about metal-free tanning?

 “I think that the demonization of traditional chromium tanning by the market is based on wrong assumptions, because chromium, like iron, is an oligoelement necessary for human life and health. Furthermore, many alternatives to traditional tanning present big uncertainties in terms of toxicity and of environmental impact. It must also be pointed out that with the alternative state-of-the-art tanning methods available at present, we will never obtain the stability of collagen that chromium offers; this means that one must use up to 30% of an alternative tanning product in order to obtain the same result that is obtained with 6% of chromium. If our goal is that of reducing environmental impact as much as possible, evidently this way we risk making the situation worse instead of better”.

We know that sometimes metal-free created problems during the depuration phase…

“During the depuration phase and the phase of recycling shavings. I want to emphasize a specific fact, that is to say, the fundamental difference between ionic tanning and covalent tanning. Metallic tanning is ionic and offers a great advantage: reversibility. In certain pH conditions, we manage to separate the metal from the protein (collagen), recovering it in its natural form, while covalent tanning, such as metal-free tanning methods, tends to denaturate it, thus making it impossible to return to the protein with which we started. This means, for example, that shaving wastes deriving from these new systems cannot be recycled and reused, as is already done instead with chromium-tanned hides, whose wastes can be transformed into bioactivators (fertilisers) for the agricultural sector”.

What do you suggest should be done?

“It is necessary to change our perspective and better communicate to the market the risks inherent in a paradigm shift that has not been carefully evaluated and analyzed. Before changing a tested and safe process such as the currently used process, we must know what we are getting into. Today we have the tools to assess the impact of a possible change before actually implementing it and causing damage. For example, we must study what happens during the depuration phase more accurately and assess risks and benefits. In the past it has already happened that products that were considered harmful were replaced with others that actually turned out to be worse: I remember, for instance, perfluorinated compounds (PFC) Êreplaced with other substances based on nanotechnologies that turned out to be more dangerous than those that were replaced”.

What are the elements on which one can act in order to improve the tanning process?

“In my view, the priorities to make the tanning process more sustainable are others. In the first place, we should work on the greening and liming phases, which remain the phases of the tanning process with the highest impact and which could be reassessed, thus obtaining significant results. Nowadays there are already biotechnological systems that make it possible to work with extremely low quantities of sulphide, and this would have been unimaginable a few years ago. Another interesting field is the development of new tannins made with organic-based waste materials in order to replace synthetic tannins. I am certain that the future has important surprises in store in this field because interesting things on molecules are beginning to be discovered: a large part of vegetable compounds contain antioxidants that have a series of useful functions that must still be discovered in detail. In the world many studies are being carried out that I am certain will produce interesting results in the near future”.