Experts on the topic of sustainability
Johann Peter Schomisch from Ecopell regarding the sustainable production of leather
Mr Schomisch, would you be so kind as to provide us with a brief insight into leather production?
First and foremost there is production with chemicals and without chemical additives. At Ecopell, we do not use any preservatives such as polyurethane (PU) to conserve the leather after the tanning or dyeing process. Traditional tanneries use preservatives to fix the dye in the leather, to make the leather water-repellent and to avoid complications in the leather’s surface structure. We do it differently. The basic property of Ecopell leather is its naturalness. The pores of the leather are open, enabling it to remain breathable. As our leather is a natural product, it is not plasticised. Naturally, some quality losses can arise if no final processing takes place, for example concerning colour authenticity and an even leather structure, which occurs even less with vegetable-tanned leather. In the furniture business, for example, where leather is used for couches and is exposed to constant sunlight, it is possible that the leather loses its colour authenticity. Additionally, temperature and air differences combined with solvents used in wall paint can cause damages to the leather structure.
You have described the numerous challenges of natural leather production. How does the manufacturing process for natural leather work exactly?
If we take a trip back in time, historically viewed, leather was tanned in hollows, using tree bark over the course of several months. In some parts of Morocco, this is still practised today. Even back then, there were problems with the deforestation of the oak forests as a large quantity of tree bark was required for tanning the hides.
Also, you ought not forget that the tannery business was always a dirty business. In the literal sense. Literally, tanneries were located a long way away from conurbations or towns in order to avoid people having to inhale the terrible stench and to make the associated water contamination problems as bearable as possible. With today’s knowledge status and modern chemicals, the unpleasant odour remains bearable. The problem with pollution has remained, if not even worsened since back then. Even in our ecopell leather production, which is exclusively treated with plant-based constituent parts (tara, mimosa and valonea), we cannot fully dispense with the use of chemical substances. In order to keep abreast of conventional tanneries and to process the required quantity of hide in the prescribed period, we use glutaraldehyde, a highly toxic chemical substance for pretanning and accelerating the tanning process which is unhealthy for man and the environment. Yet it can be broken down fully to aid the use of water-based bacteria and leaves no harmful traces whatsoever in the leather. Nonetheless, we are trying to find new ways and means. An extract drawn from olive tree leaves provides a natural alternative: a fantastic solution, however currently still too cost-intense.
Could you please provide us with more details about the substances you use for the tanning process?
There are three different tanning types. Red tanning or vegetable tanning, then the wet-white process (alum tanning with aluminium sulphate) and finally the wet-blue process (chromium III salts). The two latter processes require heavy metals which are highly environmentally harmful unless correctly used in recycling systems. We use the following plant extracts for Ecopell leather: tara (seeds from Peru), valonea (seeds, use of the skin), rhubarb (vegetable plant) and mimosa (bark). All of these substances are ecologically degradable and regrow each year. Even the wastewater, if we assume that no chemical substances and salts whatsoever have been used, can be used as a fertiliser.
However, as I already said: not all natural tanning substances are automatically good for the environment. Let us take the quebracho tree from South America as an example. The use of bark from this tree requires that rain forest is cleared, which is quite the opposite of sustainable! That is why we at Ecopell trust in plant extracts which regrow. To summarise, we use a combination of synthetic pretanning and natural tanning processes.
What temperatures can natural leather withstand?
In general, you can say that leather bleached with chromium III survives up to 150 degrees Celsius and plant-based tanned leather between 50 and 70 degrees Celsius. If too much heat is applied, the leather is ruined, it burns or hardens.
Why is chromium-tanned leather so critical for man and the environment?
Several studies have been carried out on this topic, in particular with regard to the development of highly toxic chromium VI, which can arise from chromium III salts. Research institutes such as the “Institut Freiberg Sachsen” [Freiberg Institute in Saxony] are State-supported in order to conduct studies and comparisons between leather tanned with chromium and wet-white (aluminium sulphate). Even if most of the results are positive and similar to those of plant-based tanned leather – they mostly neither incorporate final conservation processes nor waste management questions about leather bleached with heavy metals. If I think of chromium VI which can be triggered via thermal processes, I get goose pimples. Chromium VI cannot be broken down without chemical reducing agents. The production of chromium in countries such as South Africa can be extremely dangerous for the miners. Chromium III salts must be separated from iron at high temperatures in furnaces. Chromium VI can arise during this process, endangering the miners’ lives. If that were not enough, tanneries throughout the world encounter severe problems with their wastewater which is contaminated with concentrated heavy metal residues such as chromium, aluminium or salts.
Which natural and harmless dyes would you propose for the tanning process?
There are several means of dyeing leather naturally. One example is iron oxide with its dark brownish colouring. Although it is a natural and commonplace substance, it is only rarely used as a die due to its intense iron odour, its dark colour and last but not least the rigidity which occurs if the leather is not worn for a longer period. Rhubarb is a further example. As a tanning agent, the colours arising during the course of the process range from mid-brown to dark brown. With cultivated rhubarb, some 8 – 10% tanning agent is required. Waste products from the rhubarb can be used as fuel. Normally, the tanning process takes two days. In my opinion, rhubarb is the tanning process of the future. In Germany alone, huge, uncultivated rhubarb fields exist which grow from agriculturally tilled soils. Rhubarb needs nitrogen in order to grow and can be cultivated on these areas of arable land in order to return the natural balance to the soil.
Would you be so kind as to provide us in summary with some tips regarding sustainably manufactured leather?
One tip I can give you for your professional future is always to remain true to your principles. Opinions regarding the leather industry vary widely. You will often be criticised openly and must therefore always trust in the goodness of your actions. It is important not to always believe everything said or thought by experts, institutes and politicians. They are all paid by certain organisations or promoters and are therefore not able to form their own opinion. I have meanwhile been in the business for more than 20 years. I have often been very heavily criticised by the leather industry. They claimed I was mad because I already spoke against the use of chromium back in the 1980s: however they have slowly recognised that it is perhaps not such a sensible idea to exploit and contaminate nature. Trust in nature and it will remain on your side.