Analytical characterization of 5,5\u2032-dibromoindigo and its first discovery in a museum textile

Gregory Dale Smith,Victor J Chen,Melinda H Keefe,Shannon G Lieb,Amanda Holden

doi:10.1186/s40494-019-0305-7

Gregory Dale Smith, Victor J Chen + Show 3 more

Open Access

https://doi.org/10.1186/s40494-019-0305-7

Copy DOI

Abstract

The exploitation of natural sources and later synthetic molecules to generate blue to purple coloration in textiles has a long history in the dyer’s craft. Natural indigoids such as indigo, woad, and Tyrian or shellfish purple served this purpose for millennia, but in the late 1800s synthetic analogs, in particular indigotin, quickly replaced natural sources. Halogenated versions of the dye were also created, and some like 5,5′-dibromoindigo were brought to market. Interestingly, these have not been significantly discussed in the literature, nor have they been found in forensic or technical art history investigations of textiles until now. This paper reports the first identification in a museum context of this unusual synthetic brominated analog of indigo, discovered on three twentieth century Japanese yukata. Analytical data collected on reference materials using liquid chromatography-mass spectrometry, UV–visible spectroscopy, Raman microspectroscopy, Fourier transform infrared spectroscopy, and X-ray fluorescence spectroscopy are provided to assist with future identifications of this relatively unknown colorant. Density functional theory applied to 5,5′-dibromoindigo was used to confirm the experimental Raman spectrum.

Highlights

The colors blue and purple have historically been prized in textile dyeing and have led to millennia of human exploration for new sources of these colored dyestuffs
Natural indigotin (Fig. 1a) extracted from the indigo and woad plants initially served this purpose for blue textile colors [1], and the painstaking extraction of Tyrian or shellfish purple, a 6,6′-dibromoindigo dye (6,6′DBI, Fig. 1b) among other coloring compounds, from the hypobranchial glands of a variety of sea snails made purple a royal color for cloth in antiquity [2]
Identical chromatographic analysis of a historic example of Vat Blue 35 labelled “Indigo rein Badische Anilin- und Soda-Fabrik (BASF)/RB” showed the presence of indigotin, 5-bromoindigo, and 5,5′-DBI in significant relative quantities as mentioned by Thorpe and Ingold [10] and previously reported by those examining the use of bromoindigoids in organic semiconductors [16]

Summary

Introduction

The colors blue and purple have historically been prized in textile dyeing and have led to millennia of human exploration for new sources of these colored dyestuffs. LC‐DAD‐ESI‐MS Analysis of the fiber extracts was performed for the original sample set of 4 yukata with the expectation that all would be dyed using natural or synthetic indigo.

Results

Conclusion