Lichen was one Source for Medieval Dyes

Medieval Histories

7 months ago

Detail from Heroes Tapestry Metropolitan Julius Caesar

Some of the dyes used in the Heroes Tapestry in the Metropolitan from around 1400 have been identified as stemming from lichen.

Dating to around 1400, The Cloisters’ Heroes are among the oldest surviving medieval tapestries in the world. Their state of preservation is remarkable. Made entirely of wool, these hangings were both decorative and practical, keeping stone interiors warm and festive during the colder months of the year.

Since the MET’s acquisition of the Heroes Tapestries, scholars have suggested that they may have been made for Jean, Duke of Berry (1340–1416), son of John II, King of France. Of the fourteen heraldic banners in the upper part of the Hebrew tapestry, ten display Jean’s coat of arms. Of the remaining four, three show the royal arms of France and one the arms of Jean’s younger brother, Phillip the Bold, Duke of Burgundy. One of the heroes featured in the hanging is Julius Caesar wearing the imperial crown and brandishing a falcon, a specialized single-edged sabre. The Julius Caesar tapestry is currently off-view and undergoing intensive treatment in the Museum’s Department of Textile Conservation. The tapestry belongs to the artistic legacy of the Valois dynasty in Late Medieval France.

ABSTRACT

Heroes tapestry with Julius Caesar photographed by mma 1993. c 1400. © Metropolitan Museum of Art, OA, Public Domain.

As part of a long-term campaign to document, study, and conserve the Heroes tapestries from The Cloisters collection at The Metropolitan Museum of Art, organic colourant analysis of Julius Caesar (accession number 47.101.3) was performed.

Analysis with liquid chromatography–quadrupole time-of-flight mass spectrometry (LC-qToF-MS) revealed the presence of several multiply chlorinated xanthones produced only by certain species of lichen. Various lichen dye sources have been documented in the literature for centuries and are classified as either ammonia fermentation method (AFM) or boiling water method (BWM) dyes based on their method of production.

However, none of these known sources produce the distinctive metabolites present in the tapestry. LC-qToF-MS was also used to compare the chemical composition of the dyes in the tapestry with that of several species of crustose lichen.

Lichen metabolites, including thiophanic acid and arthothelin, were definitively identified in the tapestry based on a comparison with lichen xanthone standards and a reference of Lecanora sulphurata, confirming the presence of a lichen source. This finding marks the first time that lichen xanthones have been identified in a historic object, and, hence, the first evidence that BWM lichen dyes may have been used before the eighteenth century.

”Due to the age of the tapestry and the condition of the dyes, however, it has so far not been possible to definitively identify the lichen source (or sources) present in the dark brown dye. The reference specimen of Lecanora sulphurata, chosen as a candidate for its composition and population size, contained several of the chlorinated xanthones present in the tapestry, but not all. Most lichens containing these chlorinated xanthones are crustose lichens that grow on saxicolous or vegetal supports and would have to be scraped off the substrate to be used as a dye. Crustose lichens often form patches, and many species can have similar morphology. Therefore, more than one species could have been mixed, possibly along with parts of the support”, writes the authors.