Synchrotron small-angle X-ray scattering: a non-destructive technique for identifying vegetable tanned leather cultural relics

Abstract

Leather cultural relics are valuable materials for reconstructing and understanding human civilization. However, identifying the tanning agents used in their manufacture remains challenging due to the absence of rapid, non-destructive analytical techniques. This work presents a pioneering non-destructive approach, based on synchrotron small-angle X-ray scattering (SAXS), for identifying vegetable tanned ancient leathers. To validate the method, six simulated ancient leather samples (produced by vegetable, oil, smoke, aluminum, iron, and mirabilite-flour tanning) were analyzed using SAXS, in combination with attenuated total reflectance Fourier transform infrared spectroscopy, X-ray fluorescence, and pyrolysis–gas chromatography-mass spectrometry. SAXS analysis revealed distinctive diffraction patterns: vegetable tanned leathers exhibited minimal or absent peaks due to masking of the collagen fibril D-periodic structure by vegetable tannins, whereas non-vegetable tanned leathers displayed clear periodic diffraction peaks. Application of this method to seven cultural relic samples identified two as vegetable tanned leathers, a result further corroborated by phenolic pyrolysis products detected via pyrolysis–gas chromatography-mass spectrometry. This SAXS-based strategy enables rapid and non-destructive identification of vegetable tanned leather cultural relics.