Gallic acid is an important component of iron gall ink, the standard European writing and drawing ink from the 12th to 19th centuries, with a history extending to the Roman empire and the Dead Sea Scrolls. Pliny the Elder (23-79 AD) describes the use of gallic acid as a means of detecting an adulteration of verdigris and writes that it was used to produce dyes. Galls (also known as oak apples) from oak trees were crushed and mixed with water, producing tannic acid. It could then be mixed with green vitriol (ferrous sulfate) -- obtained by allowing sulfate-saturated water from a spring or mine drainage to evaporate -- and gum arabic from acacia trees; this combination of ingredients produced the ink.
Gallic acid was one of the substances used by Angelo Mai (1782-1854), among other early investigators of palimpsests, to clear the top layer of text off and reveal hidden manuscripts underneath. Mai was the first to employ it, but did so "with a heavy hand", often rendering manuscripts too damaged for subsequent study by other researchers.
^Albert W. Burgstahler and Zoe J. Bithos (1962). "Hexahydrogallic Acid and Hexahydrogallic Acid Triacetate". Organic Syntheses. 42: 62. doi:10.15227/orgsyn.042.0062.
^Pliny the Elder with John Bostock and H.T. Riley, trans., The Natural History of Pliny (London, England: Henry G. Bohn, 1857), vol. 6, p. 196. In Book 34, Chapter 26 of his Natural History, Pliny states that verdigris (a form of copper acetate (Cu(CH3COO)2·2Cu(OH)2), which was used to process leather, was sometimes adulterated with copperas (a form of iron(II) sulfate (FeSO4·7H2O)). He presented a simple test for determining the purity of verdigris. From p. 196: "The adulteration [of verdigris], however, which is most difficult to detect, is made with copperas; ... The fraud may also be detected by using a leaf of papyrus, which has been steeped in an infusion of nut-galls; for it becomes black immediately upon the genuine verdigris being applied."
^Nakai, S (2000). "Myriophyllum spicatum-released allelopathic polyphenols inhibiting growth of blue-green algae Microcystis aeruginosa". Water Research. 34 (11): 3026-3032. doi:10.1016/S0043-1354(00)00039-7.
^Mämmelä, Pirjo; Savolainen, Heikki; Lindroos, Lasse; Kangas, Juhani; Vartiainen, Terttu (2000). "Analysis of oak tannins by liquid chromatography-electrospray ionisation mass spectrometry". Journal of Chromatography A. 891 (1): 75-83. doi:10.1016/S0021-9673(00)00624-5. PMID10999626.
^Hodgson JM, Morton LW, Puddey IB, Beilin LJ, Croft KD (2000). "Gallic acid metabolites are markers of black tea intake in humans". Journal of Agricultural and Food Chemistry. 48 (6): 2276-80. doi:10.1021/jf000089s. PMID10888536.
^Pathak, S. B.; Niranjan, K.; Padh, H.; Rajani, M.; et al. (2004). "TLC Densitometric Method for the Quantification of Eugenol and Gallic Acid in Clove". Chromatographia. 60 (3-4): 241-244. doi:10.1365/s10337-004-0373-y. S2CID95396304.
^Gálvez, Miguel Carrero; Barroso, Carmelo García; Pérez-Bustamante, Juan Antonio (1994). "Analysis of polyphenolic compounds of different vinegar samples". Zeitschrift für Lebensmittel-Untersuchung und -Forschung. 199: 29-31. doi:10.1007/BF01192948. S2CID91784893.