We have both Calf and Goatskin tanned with Sumac from the 1930 s still as soft and as flexible as the day they were tanned. The work that was carried out by the then British Leather Manufacturers Research Association at the request of the British Library was aimed at improving on a good leather, and also to find ways of stopping the rot occurring in already bound books of unknown origin. Eventually they identified a little used combination tannage as the one giving the both improved stability over Pyrogallol tanned leathers, while still keeping the important features necessary for hand binding. Whilst it is a surprise to many people, vegetable tanned leather has a final pH in the range of 2.8-3.5. This can occur because the aluminium forms very stable complexes with the vegetable tans and oils, and can be seen from the fact that a normal vegetable tanned leather shrinks in water above 70 C, whilst the semi-alum leather will stand the boil.
Specialist tanneries involved in the manufacture of craft bookbinding leathers certainly do care.
Work is just about to start, funded by bookbinding leather tanneries, along with a grant from the European Union. The aim of the research is to come up with an archivally sound leather that bookbinders can use easily. Tanneries, research bodies and bookbinders from Greece, Great Britain, Italy and Germany will carry out this work.