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Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity (pKa around 6) is due to the numerous phenol groups in the structure.
T 1207 (OTTO) Tannic acid, GR Cas 1401-55-4 - used with care on objects with copper alloy components as the tannic acid can have a slight etching effect on these metals.