Equivalent light dosimetry in museums with Blue Wool Standards and optical fibers

Blue Wool Standard (BWS) dosimeters, that have been officially adopted by the International Standards Organisation for photo-induced color variation, consist of a set of wool samples which progressively and irreversibly fade when exposed to light. The samples are loaded with different light-sensitive blue dyes to show color fading with varying sensitivities to light exposure. When BWSs are exposed under normal conditions, fading occurs because of exposure to light and to the combined action of light and other environmental facets. BWSs are therefore optimal transducers for performing dosimetry of equivalent light. BWS dosimeters in combination with a miniaturized optical fiber spectrophotometer were used for continuous and real-time light equivalent dosimetry, as applied to an appropriate indoor conservation of works of art. The continuous monitoring of the occurrence of risk situations makes it possible to slow down any color deterioration and to stabilize them where possible against further deterioration. The novel instrument presented in this paper has been installed since the beginning of November 2001 at the Uffizi Gallery in Florence, in the Geographic Maps Room. Field tests will last for several months, and will be performed also in other Rooms of the Gallery in order to highlight situations of particular risk.