 Chestnut wood is a useful source of natural tannin and was used for tanning leather before the introduction of synthetic tannins.On a 10% moisture basis, the bark contains 6.8% tannin and the wood 13.4%.The bark imparts a dark color to the tannin, and has a higher sugar content, which increases the percentage of soluble non-tans, or impurities, in the extract; so it was not employed in this use.