Ever wonder what makes leather different from a decomposing body? It’s a technique used for thousands of years, invented and reinvented by cultures throughout human history. Today, only a handful of tanning methods are still used in the production of cow-hide leather, each with their own pros and cons.
Today, almost every variation of leather found in the market stems from these three techniques...
All leathers begin in the same process of basic preservation and cleaning. The process removes moisture from the hide, cleans off any hair and tissue, and establishes its pH. The prepped hide then moves to the tanning stage where the quality, appearance, and characteristics are determined.
There are two main techniques of tanning that define nearly all leather used today. Tanning is the process of permanently altering the hide's protein structure to make it less vulnerable to decomposition. This is the step that converts a hide to leather.
Tanned, natural hides in storage before going into the finishing process
1) Vegetable Tanning
Also known as veg-tanning, this natural process predates Ancient Rome and Egypt. Made by impregnating the hide with natural tannins, it can take up to sixty days to complete this initial step on a single skin.
Tannins are naturally occurring molecules found in most plants (it’s what makes red wine dry and unripened fruit tart). In leather manufacturing, these tannins are sourced from tree barks and leaves - which are ground to speed up the extraction process. Trees like chestnut, oak, and hemlock have long been used in this process. Recipes of these materials are closely guarded secrets of each tannery, giving each its own unique style of leather.
Natural hides stretched on racks and submerged in tannin baths
The hides are then stretched on racks and submerged for several weeks. Over the weeks the hides are progressively moved into vats of higher tannin concentration, resulting in a very strong, evenly tanned leather.
Once complete, the leather is in its natural color. This color is the most susceptible to color change as there are no dyes to mask the oils and UV rays it comes into contact with. To make tan, brown, black, and other colors, the natural leather is drum dyed to achieve the desired color. These colors take time to penetrate the skin, and in some cases only color the exterior sides, leaving the flesh in-between a light, natural color.
Veg-tanned leather has a natural stiffness that allows pieces to stand up to heavy wear and tear. The leather can also be “stuffed” with natural oils, resins, and/or waxes to make it more supple and give it unique characteristics. This process allows veg-tan leathers to naturally biodegrade if disposed of.
*The long history of natural leather tanning means there are a lot of wild stories and techniques, all that have had an impact on the culture of the modern leather industry. We’ll follow up with another post on these soon*
2) Chrome Tanning
Invented in 1858, chrome tanning is the process of tanning hides in chromium sulfate and other chromium salts, rather than natural tannins. Rather than weeks, this process can be completed in a day, resulting in a much more affordable leather. When the tanning process is complete, chrome tanned hides are a light blue (referred to as wet blue), a result of the chromium held within the hide. The chromium neutralizes all tonal variation in the skin to this light blue, reducing the appearance of natural marks to near zero.
Chrome hides being split to achieve even thickness
The tanned hides are then drum dyed, however, unlike veg-tanned leather, chrome tanned leather picks up dyes very quickly. This allows for the color to quickly penetrate the skin and fully color its flesh (known as “struck through”).
The final leather is a very soft, supple leather with moderate stretch. While it lends well to certain bags and clothing, it often needs extra support from other materials to maintain its shape and keep it from stretching.
Chrome Tanning is often considered a high pollutant process due to the high volumes of non-deteriorating chemicals used, however, some tanneries have go to great lengths to minimize their impact. Closed system water cycles allow some tanneries to clean and reuse water with additives like chromium sulfate still present, creating a system in which little to no chemicals are wasted. Unfortunately, these systems are very expensive and thus very rare, making it difficult to source and verify chrome tanned leather made this way.
3) Latigo Tanning
Latigo leather is created by blending the processes of vegetable and chrome tanning. By first chrome tanning then vegetable tanning, the leather takes on a very flexible quality without becoming stretchy. A useful material in horse tack, Latigo is generally made in heavier weights for straps and belts. Due to its weight and mixed manufacturing method, Latigo is often the most expensive process of tanning cow-hide.
Worker prepping Cordovan shells
Since our inception, we’ve used countless leather varieties within the vegetable and latigo tanning classifications. Each has had its own strengths, weaknesses, and overall character. The hunt for perfect leather has led us to an important realization, there is no one perfect leather. While some are especially good for one purpose, they may fail in another. Balance is the key to optimal performance, and finding the correct quality for each need is the only way to make the best leather goods.
*All images are courtesy of Horween Tannery