A compilation of technical treatises concerning painter's use of indigo has been made. Indigo painted areas of Netherlandish easel paintings were technically examined. A series of experimental reconstructions of indigo paints was made. Reconstructions have been subjected to preliminary light ageing tests. Various paint reconstructions have been chemically examined.
Sources provide severals methods for the preparation of verdigris.
It appears that the historical term 'verdigris' was used for several artificial copper greens. Painters were well acquainted with the discoloration of basic and neutral verdigris as they often warn for the darkening and turning brown of both the 'common' and 'distilled' verdigris. These remarks also provide information in what time span these discolorations occur. Furthermore, sources provide instructions on the grinding of verdigris, the media used, mixtures with other pigments and the construction of the paint layer. Various recipes were intended to prevent colour changes.