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Written Artefact Profiling Guide
Written ArtefactProfiling Guide

Photo: CSMC

Written Artefact Profiling Guide

Coloured Dye-based Ink and Paint

Natural dyes are organic coloured substances made from various parts of plants (roots, bark, fruits, leaves, stems, steeds) or from insects. Dyes can also be obtained by synthesising the organic molecules responsible for the colour. Contrary to pigments, dyes chemically bind to the material they colour, although they usually require a mordant to do so. Mordants can be naturally present in some dyes, but in most cases, they need to be added in the form of metallic salts, tannins or oil mordants. When the dye is precipitated with the mordant, a lake pigment (organic pigment) is obtained. Among the most common and well-known natural dyes we can cite indigo and woad (blue dyes), cochineal (red), lac (red to dark purple), madder (red), murex (purple), saffron (yellow), gamboge (yellow), sepia (brown).

Analytic methods:

  • VIS-NIR Spectrophotometry / FORS can allow the identification of some of the organic coloured substances, but in practice, some dyes cannot be easily distinguished with this technique. It has the advantage, however, of being non-destructive.
  • Some dyes can be identified by vibrational spectroscopies (FTIR and Raman Spectroscopy). 
  • Most other techniques are micro-destructive and require sampling. However, they are sometimes the only way to unequivocally identify some dyes. The most commonly used are chromatographic techniques (GC-MS, HPLC…)