Preserving colour of botanical wet specimens: bibliographic review and tests of historical recipes

This paper presents the results of a study on colour preservation of botanical specimens in fluid. The article includes: 1 - An introduction on plants pigments and discolouration issues specific to botanical specimens, focusing on the leaching of pigments from the specimen into the fluid, and on the denaturation of the pigments (through photodegradation, oxidation or polymerization) either in the specimen or in the fluid; 2 – An extensive bibliographic review of historical recipes invented specifically to preserve the colouration of plants as a preparation step; 3 – Results of testing some recipes on freshly prepared specimens, and their discolouration rate compared to reference specimens that were kept in 70% ethanol solution. None of the tested recipes gave results that are optimal to preserve all aspects of a specimen. In fact, colour preservation or prevention of fluid opacification came at the cost of either loss of structural stability, changes in chemical composition of pigments preserved, or loss of other colours. Ultimately, the choice of preserving the colour of wet botanical specimens should be made on the intended use of the specimen.