Museibelysnings påverkan på gula krompigment -utifrån Vincent van Goghs målning Olivskog, Saint-Rémy, 1889

Abstract

This study discuss the problems of displaying artworks containing yellow chrome pigments, reactive to the wavelengths in LED lights, often used in modern exhibitions. In the late 19th century there where a variety of chrome pigments manufactured, such as lead chromate (PbCrO4) and lead chromate mixed with lead sulphate (PbCrO4 · PbSO4). Studies have found that lead chromates with high content of sulphate and/or a certain crystal structure, tends to darken when exposed to light with short wavelengths. The main purpose has been to analyze two yellow paint samples from Vincent van Gogh’s Olive groove, Saint-Rémy - 1889, in Gothenburg art museum’s collection. Analysis with Energy dispersive x-ray spectroscopy (SEM-EDX) confirmed the presence of a lead chromate, probably mixed with zinc white (ZnO). No complete characterization of potential sulphate content in the pigment could be made. The lack of sulphur in parts of the samples and the fact that the paint after 134 years in various lighting conditions still remain bright yellow, may indicate that it is not one of the most reactive type of lead chromates. As a supplement a series of oil colours containing yellow chrome pigments was made and artificially aged for 8 400 000 lx h, with a halogen spotlight and a “warm white” LED spotlight. The experiment simulated c. 19/25 years of exposure with 200/150 lux, with respect to the museums annual open hours. The lead chromates change in colour while a zinc chromate din not. The LED light caused no more darkening of this sulphur containing lead chromate, than the halogen light. As this experiment simulated exposure for a relatively short period of time with only one sulphur containing lead chromate, the reports on the potential danger of LED lights should not be neglected.