I sent a pair of shoes back for new soles the other day, and it struck me that shoe repair is one task that is blessedly infrequent in my life. A lot of that is due to high quality soles.
At the high end of the shoe business is the lightweight, extremely hard wearing, water-repellent and breathable oak bark sole. Perhaps the world's premier source for oak bark leather is the Joh. Rendenbach Jr Tannery which has been producing oak bark sole leather since 1871.
Rendenbach soles start as leather hides that spend nine to twelve months buried in oak lined pits while tanning agents from barks and fruits fuse with the protein structure of the skin, an odorous process that uses no energy and, unlike many 19th century indusrial processes, is completely biodegradeable.
Oak, spruce and mimosa bark as well as valonea fruit provide the active ingredients in the tanning procss. Oak bark possesses a pure tannin-content of 8-10%. Mimosa bark is 30-35% tannin, and spruce is used for its high sugar content. The valonea tree has fruit whose spines have a tannin-content of 30-35% and possess similar tanning properties to oak bark.
Thanks in large part to that sole food diet, the useful life of a high quality sole like Rendenbach's is several times that of lesser soles.