Measuring photostability through glass: the application of microfading testing to the study of framed pastel artworks

Abstract

Paper‐based heritage objects on exhibition are typically framed using a transparent glazing material such as glass or acrylic. This often makes the task of measuring their light fastness a difficult one since cultural institutions may have unframing restrictions, especially for large‐format objects. However, a testing programme recently conducted at the National Museum in Krakow has revealed that in certain cases it is possible to obtain colorant stability information directly from a framed object. Microfading testing results are reliable if the distance from the object to the protective glazing is adequate to allow proper illumination and collection of reflected light. This paper presents a case study of six large‐format pastels on paper by Stanisław Wyspiański, one of the most outstanding and versatile artists at the turn of the twentieth century in Poland. Some of the orange and pink areas showed higher sensitivity to light with fading rates that remain within the Blue Wool 1–2 range. The objects have been classified according to the light sensibility of their colorants, and this information has allowed development and implementation of exhibition guidelines that serve to minimise the degradation associated with museum illumination. In addition, scientific imaging, microfading data and computer analysis of the images have allowed virtual representation of the potential colour changes that these artworks may experience as a result of uncontrolled and long exposure to gallery illumination.