- Catherine Higgitt, Head of Science
- Colin McEwan, Head of Americas section
- Thibaut Deviese, scientist
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Studying colourants: methodological approach
The study of Andean colourants, both past and present, is analytically challenging because of the wide range of biological sources used, their chemical complexity and the relative lack of information about colourant technologies. It is therefore important to collect securely identified and locally grown natural plant materials and produce dye and pigment samples according to known recipes.
These reference samples are essential for the development of the analytical protocols, mainly based on High Performance Liquid Chromatography (HPLC), and databases to enable better understanding of colourant technologies before using samples from museum objects.
A key to the success of the project is access to well characterised reference materials – both samples of biological raw materials and samples of pigments or dyed textiles produced following well-documented recipes and representative of traditional technologies (where known). Colleagues at the Instituto del Patrimonio Cultural Espanol (IPCE) are providing expertise in Central and South American dyeing technologies and an extensive collection of reference samples (about 400 dyed camelid and cotton samples representing numerous dyes and technologies). Additional materials are being obtained through partners, and directly in South America, where contact has been made with traditional dyers and the collection of plants will further expand available reference materials.
The analytical approach adopted relies on the molecular-level characterisation of the organic colourants and is therefore primarily based on the use of HPLC with a photodiode array detector (HPLC-PDA). Optimisation of the extraction procedures has been an important first stage in the study, and the analytical study of archaeological material has started with a study of the colourants found in fibres associated with Andean weavers’ workbaskets.
HPLC analysis of reference materials and of archaeological and historical Andean textile samples is being complemented by the investigation of degradation mechanisms using experimental material. The chromatographic study is also supported by a range of other analytical and imaging techniques including HPLC-mass spectrometry, scanning electron microscopy (SEM), Raman spectroscopy and multispectral imaging/spectroscopy available at the British Museum and through partners. These techniques provide complementary information about dyeing technology including information about mordants used and the nature of the substrate.