LEATHER TANNING PROCESS
We’ve been working together with the Sheong Shi Tannery in Kolkata since 2010 to improve, expand and promote the use of our eco-friendly leathers. Patrick and Veronica, the owners of the Sheong Shi Tannery are very passionate about the eco-friendly leather project. Together with Patrick and Veronica we are constantly working towards promoting our leather. We have noticed that interest in sustainable leather tanning processes has increased in the last years. This is great news, because it means that the industry is becoming more concerned with their environmental impact.
In 2015 we won the Sustainable Leather Awards, an award that is given out to an initiative or idea in the Dutch leather sector with a positive (indirect) effect on people, animals and the environment in developing countries.
THE TANNING PROCESS
When you’re flaunting your O My Bag it is hard to believe that once your bag was a raw hide. In a corner of the tannery we find the raw hides. It is easy to differentiate our eco-hides from the other hides at this stage, as our hides look white instead of blue. The bio synthetics used to tan the eco-friendly leather results in a semi-finished leather that looks white-tinted. That is also why our organic tanning method is called “wet white tanning”. The off-cuts of this wet white tanned leather can be recycled or used as fertilizer, in contrast to wet blue tanning methods (chrome-hides).
As the eco-friendly leathers aren’t treated with heavy chemicals, they can only be preserved for 6 weeks, so it can’t be held in stock by Patrick, compared to his other leathers. This is one of the reasons why the production is more difficult to manage and also why the production-time of our bags is so long, the process of just tanning the leather can take up to 8 weeks!
A common question we get at O My Bag is, how it is possible that Patrick can get a hold of cowhides in India, as it’s common knowledge that cows are sacred animals over there. Only few people are familiar with the fact that Islam is the second-largest religion in India. In Kolkata around 33% of the inhabitants are Muslims and eat meat. The hides are a by-product of the meat industry.
After the preparatory stages when the hide is prepared for tanning by removing many of the unwanted raw skin components, the hide is ready for the tanning. Tanning is the process that converts the protein of the skin into a stable material that will not decompose and is suitable for a wide variety of end products, such as leather bags and accessories. The hides are loaded into a drum and immersed in the tanning liquor. The hides soak while the drum slowly rotates and the tanning liquor slowly infiltrates the full hide. Regular checks by the workers are necessary to see if the penetration is even. After the tanning, the skin goes into the crusting phase when the hide is thinned (which is called shaving), re-tanned and lubricated. Most importantly, in this phase, the skins are dried, softened and receive their color. The last phase of the tanning process is the finishing, where surface coating is applied. Our eco-friendly leathers hardly have any finishing, this leaves them very open to change during use and gives them their vintage look over time. It incorporates the fat on our skins and the shine because of rubbing against our clothes.
The tanning process of eco-friendly leather is comprised of a combination of synthetic tanning agents and natural vegetable extracts. In the making of our leathers, Patrick avoids the use of harmful chemicals like chromium, heavy metals, formaldehyde, short-chain chlorinated paraffin, volatile organic compounds, alkyl phenol ethoxylates and so on. The leather is tested regularly by SGS, an independent inspection agency, to check the chemicals (not) used.
Research has shown that a significant part of the environmental impact of leather is in the manufacturing process. Therefore, it is not only the chemicals used in the tanning process that should determine how eco-friendly the leather is. To combat this, Patrick regularly accesses the tannery in terms of:
- Management of restricted substances
- Energy consumption
- Air emissions
- Waste management
- Environmental management systems
- Water consumption
- Control of manufacturing processes
- Effluent treatment
- Traceability of material
Patrick has built a water reservoir to collect rainwater during monsoon season. This water is used later in the production. In addition to this, the used water is purified in a central purification facility.
To minimize the energy consumption, the building is made in such a way (U-shape) so that daylight can come in everywhere. Patrick and Veronica also developed the layout/machines so that one motor can give energy to more machines at a time.
Installed within the tannery of Patrick and Veronica is also a primary effluent treatment plant, which is definitely something that they are proud of. The function of this plant is to segregate the heavier suspended particles from the dissolved chemicals in the waste material that goes out of the tannery. The waste from all the tanneries is then sent to the Common Effluent Treatment Plant (CETP) where it is treated. (This process is closely and regularly monitored by the Central Pollution Control Board and the West Bengal State Pollution Control Board. Also a regular check of the Primary treatment plant within the tanneries is done by the WBSPCB and the Calcutta Leather Complex Tanners’ Association).
Men and women are paid equally
Rain water harvesting system installed