For those that are interested in the complex and nuanced leather industry, I found an interesting and detailed study of the leather selected and used to clad the Brendan boat. In 1976 Tim Severin crossed the Atlantic from Ireland to Newfoundland in a boat designed and made from plans found in the 8th century Latin texts describing the voyages of St Brendan in the 6th century.
At the time there was much skepticism that a leather boat would withstand months at sea , what with huge waves , gales , whales , beaches , rocks , ice and the like.
Tim and his team proved the doubters wrong
The tanning and conditioning of leather is highly variable , depending upon the intended use.
Modern leather is chemically/synthetically tanned - chrome salts. It's quick and relatively cheap; you get a soft pliable product.
Tanning with vegetable matter (e.g. bark , animal fats/oils) is the ancient method but takes months and is labour intensive. The leather acquires characteristic odours and special characteristics.
The saddle leather used in the Grenadier option is different from seat leather. Products used to treat modern leather are different to those to treat
old style leather.
Here are some tests pertinent to the 1976 recreation of St Brendan's voyage. It's not an exact science but there's a lot of science in it!
For the record , they waterproofed using wool grease , and it stank.