The tannins used in different parts of the world has given huge diversity to the options of tanning vegetable leather. Countries like France were famous for chestnut, the UK for oak and Africa for Acacia. Places like Central America used mangrove and this caused issues because of the damage it did to the coast. Tanners have not used mangrove for a very long time and in the 20th century the damage to mangroves was done building tourist resorts or shrimp farms.
In the US oak and hemlock became the two materials used. Tanners had to be near to the forests as the tanbark was fragile and perishable, and a huge volume was needed as only about 10% of the weight consisted of active tanning agents and the rest was thrown away or burned as fuel.
The first patent for leaching tannin from tanbark in the US was issued in 1791 but was not used commercially, and in 1880 only oak bark, hemlock bark and sumac were recognized as tanning materials. But that was the year of change as the industry decided it was time to use extracts, with hundreds of new patents being issued in just a few years.
Transporting a leached extract which contained all the active ingredients needed for tanning reduced the weight of the bark by about 90% so the location of the tannery relative to the forest became much less important and suddenly the globally historic aspect of tanning being a regional specialization according to the availability and nature of the local bark declined.
In the US we saw oak tanning starting in hemlock regions and hemlock tanning in oak regions. Tanneries in the hemlock region of the US started a production of what became the famous “Union” leather which mixed oak and hemlock extracts.
This was a fundamental change for the leather industry as tanneries were now able to be built wherever there were large supplies of hides. Given that refrigeration was just coming into use in the USA and meat packing companies were about to be built at the big transportation hubs like Chicago the implications are obvious.
Tanners can now buy extracts of every type and variation and use them in a great number of mixes in a pure vegetable tanning process or to aid the improvement in the characteristics of other tannages.
Photos courtesy of Mendocino Coast Model Railroad and Historical Society website, which has more historical information on oak bark tanning.