On the Use of Bistre in Transparent Wood Varnishes: Analysis, Application and Reconstruction.

Finishing treatments applied to cabinetwork are an important aspect of historical decorative interiors. Veneers and solid woods were treated with transparent varnishes to highlight the grain and enhance the intrinsic colour of the wood, with modifications to tone and wood grain often undertaken before the varnish was applied. The intention was not to obscure the surface as with polychrome coatings, but rather to embellish the natural wood prior to varnishing. Ageing processes and losses of original layers, e.g. due to removal during restoration treatments, mean that very little evidence of these finishing layers remains and their significance has therefore largely been forgotten. Literary sources refer in particular to staining with a mordant to adjust and/or modify the hue of wood. But some historical treatises also describe the application of black-brown washes or glazes to enhance the textural appearance of the wood. One organic colourant used for washes is bistre (or bister), a finely dispersed, organic pigment of a warm, deep, transparent brown hue that contains characteristic hardwood pyrolysis products. In order to clarify the nature of bistre as discussed in this article, reconstruction processes carried out according to historical sources are described. Gas chromatography–mass spectrometry analysis is suggested as a possible analytical method to identify typical marker compounds in both reference materials and historical samples dating from the sixteenth to nineteenth centuries. [ABSTRACT FROM AUTHOR]