| Abstract: | SUMMARIES. To assess the scope of computer-match predictions of formulations for use in ceramic restoration, a database of visible reflectance spectra of the pigments used by ceramic conservators has been compiled. Because of the problems associated with metamerism, prime attention has been given to blue pigments. In addition to a range of colours of standard pigments, 14 blue pigments were investigated in total, including several variants of ultramarine, copper phthalocyanine and indigo. Uniform drawdowns were prepared from pigments in Paraloid B72 dissolved in acetone (25:75 by mass). Modification of a commercial colour-match prediction computer program was necessary to enable the spectrophotometer to achieve reliable colour measurement of non-flat ceramic glazes by means of a special adaptor, comprising a Teflon collar. The success of this approach was validated by means of a set of 12 standard coloured tiles. The colour deviation between the normal and adapted readings was acceptable. A variety of blue and white Chinese ceramics and Dutch tiles were investigated. It was found that visually acceptable matches of these blue ceramics with pigments from the database were obtained. Furthermore, because the system matches under three illuminants (A, D65 and TL84) these matches were found to be free from metamerism. In addition, it was found that some of the blue pigments under investigation were redundant. These pigments could be omitted from the database with only a very small decrease in its matching power. Relevant reflectance spectra for ceramic glazes and pigment combinations are reported. |
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