Colorimetric analysis of two watercolours used in retouching

Prussia blue and phthalo blue have a particularly importance in retouching because they provided a considerable amount of green and they are also transparent, which will give strong clear greens when needed during the retouching practice. The objective of this experiment is to evaluate the colorimetric change of the two cited pigments, in watercolours, after being exposed to direct sunlight for one year, comparing the results with another two samples protected from solar radiation, and also analyse the spectral curves similarity between both. The pigments are of the brand Artist´s Watercolour of Winsor & Newton. Colour variations were determined in the uniform colour space called CIELAB. The results show that phtalo is more stable than Prussian blue.