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Metamerism may occur if modern substitutes for traditional artists' pigments are used when restoring a painting. Retouchings which match in the daylight of the restorer's studio may become visible when the painting is viewed in different lighting conditions or is photographed. In practice the matching of blue pigments has proved to be particularly difficult. Metamerism can be avoided by selecting modern substitutes with similar spectral reflectance curves to the traditional pigments. It is shown that manganese blue is the most suitable modern pigment for matching azurite and French ultramarine for matching genuine ultramarine, and that it is inadvisable to try matching Prussian blue with French ultramarine, cobalt blue or cerulean blue. Pigments are also recommended for matching smalt and indigo provided these pigments have not undergone a degenerative colour change. [ABSTRACT FROM AUTHOR]

An introduction is presented which discusses various papers within the issue selected from the International Institute for Conservation of Historic and Artistic Works' 26th Biennial Congress held in Los Angeles, California.