I make leather wallets and belts exclusively out of vegetable tanned leather. Why? Because I will never get over the way that natural, unfinished vegetable tanned leather ages; it develops a unique patina over time, absorbing oils from your hands, the indigo from your jeans, and UV light from the sun. The character it develops mirrors the life of its user and becomes a true reflection of how you look after the things you own. As it wears and ages, vegetable tanned leather will develop sheen in high stress areas, and darken throughout its lifetime.
What is tanning?
Tanning a hide is very different to what we do at the beach (by stripping off and bronzing ourselves under the sun). Tanning involves soaking in huge drums filled with a solution that preserves the hide, preventing it from decaying and becoming stiff, thereby turning it into leather. After the hair is removed and the hide is degreased, tanning serves the purpose of removing water molecules to reduce the risk of hydrolysis. Otherwise, water would facilitate the separation of chemical bonds within protein molecules, which means that the hide would decompose. The tanning process is somewhat the same regardless of what kind of animal the skin came from, but for the purpose of this article I’ll be speaking primarily of cow hide, given that this is what I use to craft all of my products. There are many different methods of tanning: alum tanning, aldehyde tanning, even brain tanning, to name a few - but the predominant forms today of turning animal hide into leather are chrome tanning, and vegetable tanning.
Chrome tanning
Chrome tanning uses chemicals, acids, and salts, including chromium sulphate (hence the name) to transform animal hide into leather. Chrome ions replace the water molecules that are drawn out of the hide to make the finished leather pliable and soft. If it were simply dehydrated, it would become stiff as a board and pretty much useless for anything other than making dog chews (think of rawhide). After it is tanned, and before it receives its finishing treatments and dyes, chrome tanned leather has a pale blue colour, and so can be referred to as “wet blue”. Because of this, chrome tanned leathers are always dyed, treated, and given heavier finish coatings to achieve their desired look and hand (feel). This is the reason why chrome tanned leather struggles to develop a patina, and will not darken over time. It stays more or less the same colour it was initially dyed for its entire useable life, which can be almost any colour, and has good water and and stain resisting properties. This is great if the designer of a bright green handbag, for instance, would like the colour and finish to remain relatively unchanged throughout its life, and for there to be little maintenance required to care for the bag.
Tannery in Kanpur, India. Image via National Geographic.
After chrome tanned leather is tanned, it is put into huge drums where it is tumbled with dyes, oils and conditioners that help preserve the leather and give it its intended colour. It can be a slippery slope for manufacturers that attempt to cut costs: by simply reducing the amount of time that the leather is drum dyed, or by using cheaper dyes, a tannery can save a lot of money and produce more leather in the same time. The end result is leather that has a drastically reduced usable lifespan, and will eventually crack. It is dyed on the surface, but the oils and waxes don’t penetrate to the centre of the leather, leaving a blue core. When buying chrome tanned products, check the edges of the leather. They are often painted as a way to finish the edges, but if not, you will want to see if the leather is the same colour all the way through. This is quite easy to hide in the final product, just by painting the edges or by turning them in on items like bags or furniture, so it can be difficult to gauge quality and know exactly what you are buying. Make no mistake, there is definitely good chrome tanned leather to be had, however as vegetable tanned leather supplies only 10% of global leather demand, and only the best tanneries with a long history behind them produce it, its quality is easier to assure. Plus, due to the fact that vegetable tanned leather is produced on a longer time frame, and naturally has a higher cost, it is usually destined for use in high end leather goods, the manufacturers of which would not risk their reputation to profit in the short term.
Today, chrome tanned leather is used in the vast majority of leather products available to buy; up to 80-90% of the world’s leather is made in this way. Vehicle interiors, furniture, shoes, bags, and clothing are all great examples where chrome tanned leather is the perfect choice. It is softer, thinner, and more supple than vegetable tanned leather, and stretches easily as well, making it a good choice in shoemaking, where the leather upper is stretched over a last. Chrome tanned leather is not very labour intensive and can be made within a day or two, making it the most predominant form of tanning after it was first invented in 1858. It is, however, particularly harmful to the environment. Solutions of heavy metals can make for hazardous working conditions, and in Kanpur, India, which is the world’s largest exporter of leather, the vast majority of waste water is often dumped untreated straight into the River Ganges. This has had impact on the health of local communities, and when chromium ions, arsenic, and lead are leached onto surrounding farmland, contaminating soil, the related health issues can be quite widespread.
Vegetable tanning
So what is vegetable tanning? It is the oldest and traditional form of tanning, dating back almost to 6000 BCE. Our ancestors used vegetable tanned leather to make sandals, shoes, liquid containers, shields, and armour. The process has remained largely unchanged over millennia and it is the most “natural” way to produce leather. Vegetable tanning takes several months and considerable skill to properly tan a hide. Usually only tanneries with a significant history produce leather in this way today; there is only one operating oak bark tannery in England, and two remaining in the USA. Italian leather is renowned for being of high quality, and for good reason: there are more than twenty vegetable tanneries operating in the Tuscany region alone.
Vegetable tanned leathers are more commonly dyed in earthier tones, more natural to leather: browns, shades of tan and perhaps burgundy. Bright colours don't lend themselves well to the properties of vegetable tanned leather because of how it can change appearance over time. When left unfinished its natural colour is cream/pink, sometimes almost white, although over time, and with use and sun exposure, it will darken to a deep rich brown.
Vegetable tanning is so named because it uses the “tannins” that are naturally occurring in vegetable matter to tan the hide. They are a yellow-brown organic substance found in bark and other plant tissues; they contribute to tea’s flavour and are the reason that red wine can have a dry mouthfeel. This is because tannins bind easily to protein molecules and encourage water to be drawn out of your skin. In the tanning process water molecules are removed from the hide, but instead of chrome ions taking their place, they are replaced with tannins from the bark of chestnut, oak, and mimosa, most commonly. As a result, vegetable tanning is comparatively better for the environment, given that the tanning solutions use only natural materials and the scale of production is much smaller than chrome tanning. Tannins coat the collagen fibres in the hide, preserving it and changing its material properties. Vegetable tanning results in thicker, sturdier leather because tannins have a larger molecular structure than the chrome salts used in chrome tanning. This makes vegetable tanned leather the obvious choice for saddlery, straps, belts, bags, and high end leather goods that seek the unique aesthetic, heritage and durability that only vegetable tanned leather can provide.
Tannery in Tuscany, Italy.
So why do I use vegetable tanned leather?
For Rivet & Chain, I choose only the best leather available. It takes considerable time to cut, stitch, burnish and finish just one leather wallet, so I use only the highest grade leather that complements the time and effort put into making my products. It is also possible for me to dye and finish natural tooling leather myself, so that I can be flexible in my production and have plenty of colours to offer.
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