Bark or vegetable tanned leather is most recognizable to us as boot or shoe leather, although most modern types are made with chromium acids (toxic stuff). This type of leather comes to us mainly of old North African, Middle Eastern and European lineage. This is the way by which we came to sturdier footwear, harness and saddle for working with and riding horses, and other goods; in times gone by waterproof vessels, tents, sails and boats - even ocean faring ones. Far too often is leather looked at as a luxury material and an option among many, not as having played such an integral role in human culture. Until very recently, bark-tanned leather was the only material serviceable enough for farmers to shod themselves and outfit the horses for work, indeed for any cold weather footwear. This was the leather used in all old factories as the sole means of running power - via leather belts - from steam engines. From this tannage comes the sturdiness and strength that we associate with quality leather, its durability and high water-resistance, its polish and beautiful grain texture. This is a much stouter, typically thicker, non-elastic, much less breathable leather.
Bark or vegetable tanned leather, so called because it is the tannins present in plant matter - oak bark most traditionally in Europe, but also sumac leaves among others - that do the majority of the work. The good and old word "tan" comes to us from a celtic word for oak - "tann." Depending on the thickness and stoutness of the hide, they may be bathed in the solutions for weeks, months, or a year while they slowly and incrementally eat up the tannins, actually adding weight to the leather. Leather making treatises published up until the 1900's even refer specifically to "feeding" the skins and keeping them "nourished."
The real craftsmanship of this leather lies in the care and attention paid to the grain of the leather, its surface. Starting right from how the skin is first dried, then soaked and through the dehiring - the removal of the hair without damaging the follicles.. In the final stages, the grain must be oiled, dried properly and worked to a finish to bring out its suppleness, rich texture and lustre. This sometimes only millimetre thin layer is the magic, having the alive quality of not drinking while breathing -resisting the absorption of water while permitting the passing-out of water vapour, a fundamental capacity of skin - a responsive and agile membrane somewhere between inside and out.