Vegetable-tanned leather, also used in Knot’s straps, is leather tanned with tannins derived from plants. It is prized for its natural texture, durability, and resilience. Yet because it takes far more time and cost than the mainstream chrome-tanning method, vegetable tanning today accounts for only about 20% of all leather production. Even so, a handful of makers have remained steadfast in protecting this tradition, passing it down for more than a century. Let’s take a closer look at what makes it so special.
The Tanning Process: from Hide to Leather
The history of leather and humankind goes back to ancient times, when people first used the hides of hunted animals as protection from the cold. At first, hides were used raw, but because they quickly spoiled or became stiff as they dried out, people began experimenting – smoking them, soaking them in plant juices, and more – to make them easier to use. Out of these efforts grew the art of tanning: binding tanning agents to the fibers of the hide to create supple, durable leather.
In Japan, chrome tanning – using basic chromium sulfate as the tanning agent – was the first method to be introduced. About twenty years later, in 1869, tannin tanning, which uses tannins naturally found in trees and plants, was introduced. Today, about 80% of leather worldwide is chrome-tanned, with only the remaining 20% made using tannin tanning. Yet this method has deep roots, with the earliest known products dating as far back as ancient Egypt.
What Makes Vegetable-Tanned Leather Special
Tannin is the “astringency” contained in plants. By slowly binding tannins with collagen, the fibrous protein in hides, the leather gains firmness and resilience. Over time, vegetable-tanned leather produced through this method takes on a rich patina, changing color and texture with age in a way that makes each piece unique.
However, this is a meticulous and demanding technique, with natural materials and meticulous processing. From raw hide to finished leather, it takes around six months, and requires significant labor and equipment. Because of this, many tanneries specializing in vegetable tanning have been forced to close over time. Nevertheless, some leather makers continue to uphold this method with unwavering dedication, preserving a tradition that has endured for more than 100 years.
Vegetable-Tanned Leather Through Twenty Steps of Craftsmanship
Salted raw hides being washed in a drum
The process begins with salted raw hides from cattle or horses, which are placed in enormous drums and “washed” for 24 hours to remove salt and impurities while rehydrating them. Next, they are soaked in lime to loosen the hair and relax the collagen fibers. Excess fat and tissue on the inner side are then removed in a step called “fleshing”. After this, deliming and bating neutralize the hide in preparation for the vegetable-tannin solution, where the actual tanning takes place. Once tanned, the hides are treated with high-quality oils for softness and sheen, stretched by machine in a “setting” process, and then dried. If dyeing is required, the hides undergo additional tanning and setting before being made ready for shipment.
The process of stretching leather using a machine
Tanning itself can be done in different ways. Some craftsmen use a drum method that works tannins into the hides in two to three days, while those who are more particular about the leather’s texture immerse the hides in pits for about a month to allow gradual, thorough penetration. Each tannery and craftsman brings their own focus and expertise to these steps. Additionally, the setting process may be repeated multiple times to further enhance durability and resilience.
This level of care – even in processes invisible to the end user – is part of what makes Japanese leather unique. While Italian leathers often emphasize bold coloring and are dyed to a fine finish, many Japanese makers leave their vegetable-tanned “nume” leathers undyed, confident that the raw material itself has inherent beauty worth appreciating.
Because each piece is finished with painstaking attention until the craftsman is fully satisfied, Japanese vegetable-tanned leather shows differences in durability and feel that become apparent over years of use. Increasingly recognized as a “Japan Brand”, it represents a tradition that continues to evolve while staying true to its roots. We look forward to seeing this heritage preserved for generations to come.