Identifying Brazilwood’s Marker Component, Urolithin C, in Historical Textiles by Surface-Enhanced Raman Spectroscopy

Brenda Doherty,Catherine Higgitt,Maria Perla Colombini,David Peggie,Aldo Romani,Ilaria Degano,Costanza Miliani

doi:10.3390/heritage4030078

Brenda Doherty, Catherine Higgitt + Show 5 more

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https://doi.org/10.3390/heritage4030078

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Journal: Heritage	Publication Date: Jul 25, 2021
Citations: 10	License type: CC BY 4.0

Affiliation: National Gallery, University of Pisa, University of Perugia

Abstract

The fugitive nature of the colorants obtained from sappanwood (Caesalpinia sappan L.) or the South American species commonly known as ‘brazilwoods’ (including other Caesalpinia species and Paubrasilia echinata (Lam.)) makes the identification of brazilwood dyes and pigments in historic artefacts analytically challenging. This difficulty has been somewhat alleviated recently by the recognition and structural elucidation of a relatively stable marker component found in certain brazilwood dyes and pigments—the benzochromenone metabolite urolithin C. This new understanding creates an ideal opportunity to explore the possibilities for urolithin C’s localization and identification in historical artefacts using a variety of analytical approaches. Specifically, in this work, micro-destructive surface-enhanced Raman spectroscopic methods following a one-sample two-step (direct application of the colloid and then subsequent exposure of the same sample to HF before reapplication of the colloid) approach are utilized for the examination of four historical brazilwood dyed textiles with the results confirmed via HPLC-DAD analysis. It is shown that characterization of reference urolithin C is possible, and diagnostic features of this molecule can also be traced in faded historical linen, silk and wool textiles, even in the presence of minor quantities of flavonoid, indigoid and tannin components. The exploitation of the same micro-sample through a series of SERS analyses affords a fuller potential for confirming the characterization of this species.

Highlights

Brazilwood dyestuffs and pigments are derived from a number of closely related and often historically confused species of trees of the Leguminosae family
SERS spectrum from a reference sample of a brazilwood lake pigment, it was instead necessary to routinely pre-treat the sample with HF acid vapors to liberate the main dye constituent from its inorganic substrate, an action that allows for a greater adsorption of dye molecules onto the SERS active substrate (Figure 2ii)
Approach was suitable for use on historical textile samples and it was subsequently successfully applied to minute samples from four historical linen, silk and wool textiles dyed with brazilwood and showing varying degrees of fading

Summary

Introduction

Brazilwood dyestuffs and pigments are derived from a number of closely related and often historically confused species of trees of the Leguminosae family. Heartwood from the so-called ‘soluble redwoods’, sappanwood (Caesalpinia sappan L.) from Southeast Asia and several South American species commonly called brazilwoods (including Caesalpinia brasiliensis L. and Paubrasilia echinata (Lam.)), contain brazilin, the main colorant in brazilwood dyes. The fugitive nature of brazilwood has been documented since the Middle Ages, and its use as both a dyestuff and a pigment has been regulated or proscribed as a result, for use as a sole colorant [2].

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