Review Vegetable Tannins Used in the Manufacture of Historic Leathers Lina Falcão 1,2 and Maria Eduarda M. Araújo 2,* 1 Artistic Studies Research Centre, Faculty of Fine Arts, University of Lisbon, Largo da Academia Nacional de Belas-Artes, 1249-058 Lisboa, Portugal;
[email protected] 2 Centre of Chemistry and Biochemistry, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Lisbon, Campo Grande, Edifício C-8, 1749-016 Lisboa, Portugal * Correspondence:
[email protected]; Tel.: +351-217-500-968 Academic Editor: Hideyuki Ito, Tsutomu Hatano and Takashi Yoshida Received: 28 March 2018; Accepted: 1 May 2018; Published: 3 May 2018 Abstract: In this review, a brief description of how animal skins were transformed in leathers in Europe using different vegetable tannins will be presented. Special attention will be dedicated to the description of the type of tannins and the characteristics of the most important type of historic leathers thus obtained. The text will also focus on the description of the techniques used in the identification of these tannins in historic objects: colorimetric tests and spectroscopic analysis. Keywords: tannins; vegetable tanning; European historic leathers; colorimetric tests; spectroscopy; UV-Vis; FTIR 1. Introduction Natural tannins, stricto sensu, are polyphenolic compounds of vegetal origin with the property to precipitate proteins. It is assumed that the oldest application of this tannins chemical property in technology is the stabilization of animal skins protein against putrefaction [1]. According to some authors [2–5], it may have been by the end of Neolithic period and in the eastern Mediterranean region that man began to use, incipiently, plant materials, such as leaves, twigs, fruits, barks or roots, to prevent animal skins degradation, transforming them into a more durable and useful material.