Photochemistry of Artists’ Dyes and Pigments: Towards Better Understanding and Prevention of Colour Change in Works of Art

Abstract

The absorption of light gives a pigment its colour and its reason for being, but it also creates excited states, that is, new molecules with an energy excess that can be dissipated through degradation pathways. Photodegradation processes provoke long-term, cumulative and irreversible colour changes (fading, darkening, blanching) of which the prediction and prevention are challenging tasks. Of all the environmental risks that affect heritage materials, light exposure is the only one that cannot be controlled without any impact on the optimal display of the exhibit. Light-induced alterations are not only associated with the pigment itself but also with its interactions with support/binder and, in turn, are further complicated by the nature of the environmental conditions. In this Minireview we investigate how chemistry, encompassing multi-scale analytical investigations of works of art, computational modelling and physical and chemical studies contributes to improve our prediction of artwork appearance before degradation and to establish effective preventive conservation strategies.

A 1000-year-old mystery solved: Unlocking the molecular structure for the medieval blue from Chrozophora tinctoria , also known as folium

“…1), but in contrast to the transient radical species in M. perennis, the blue in C. tinctoria has a stable glycosylated dimeric structure and is therefore water soluble. To summarize, this molecular structure is key to identifying folium in works of art and to studying the structural, electronic, and reactive properties of this complex dye (32,33). This will pave the way for evaluating conservation conditions and the determination and planning of the best preservation strategies.…”

Non-Linear Microscopy: A Well-Established Technique for Biological Applications towards Serving as a Diagnostic Tool for in situ Cultural Heritage Studies

“…Aging, inappropriate handling, pollution, temperature, light, bacteria or insects, and other factors may affect the color of the object, or may cause cracks, chemical reactions, or layer detachment and lead to damage. Degradation phenomena related to paintings, paper, plaster, glass, wood, and metal have been thoroughly studied [4][5][6][7][8][9][10]. The earlier the restoration begins, the more effective and the less expensive it is.…”

“…Clearly, these methods should be non-destructive; otherwise the diagnostics can be more harmful than the deterioration itself. There has been research on works of art, by computational modeling, and physical and chemical studies, that improve our prediction of artwork appearance before degradation and establish effective preventive conservation strategies [4].…”

Kandinsky’s fragile art: a multidisciplinary investigation of four early reverse glass paintings (1911–1914) by Wassily Kandinsky

“…5c, spot 4). Cadmium carbonate was reported in early 20th-century paintings by Henri Matisse, James Ensor, Pablo Picasso and Edvard Munch and is often accompanied by other Cd phases like sulfates, oxalates and chlorides [58][59][60][61][62][63][64]. Synchrotronbased spectroscopic methods applied on the microscale have allowed researchers to reveal the distribution of various cadmium compounds and confirm that cadmium carbonate can occur as a photo-degradation product of cadmium yellow and as a remnant of the production process [55,56].…”