How to Preserve Photographic Artworks for the Future: Chemical and Physical Interactions and Implications for Conservation Strategies

Abstract

The combination of photographic prints with additional materials such as paints, varnishes, glues, etc. has given rise to a new type of artworks known as photoworks or photographic art. These photoworks have become a important part of our cultural heritage, and are being recognised as contemporary artworks in many international musea. However, photographic (gelatine-based) prints have not been designed to persist for long periods of time, such as might be expected from more traditional artworks like paintings, and this discrepancy is further pronounced in combined photoworks. Hence, many combinations of materials give rise to unforeseen and undesirable additional interactions. In this thesis, the combination of photographic prints and additional materials is investigated from a chemical and material science perspective for the first time, aiming to elucidate degradation mechanisms and thereby assist the long-term storage and preservation of these valuable artworks. The photowork Dutch Grey (1983) by Dutch artist Ger van Elk is an example of such a degradation; it consists of a silver gelatine photograph partially covered with an unknown paint layer and a varnish. In turn, this paint layer is largely covered with an off-white, crystalline efflorescence. By combined use of µ-FTIR, SEM-EDX and a GC-MS-based derivatization procedure, samples of the paint layer were found to consist of an alkyd-based resin, while efflorescence samples from Dutch Grey were shown to consist of crystalline, dimeric and saturated free fatty acids (FFAs). Five additional alkyd-based artworks from the collections of various museums in the Netherlands were also investigated, and an equivalent efflorescence was found on all of these works. The underlying photographic gelatine catalyses efflorescence formation, while varnishes applied on top may diminish or aggravate efflorescence formation depending on composition and thickness; these effects can be understood in terms of the hydrolysis-based formation mechanism of the efflorescence. Interactions between photographic materials and applications can have an effect on the photograph as well, such as found in the photowork Russian Diplomacy (1973), another work by Van Elk. In this work, black photographic areas have discoloured to purple, damaging the meaning of the work. Upon removal of the protective Plexiglas plate, a strong smell of acetic acid was immediately apparent. A series of model dyes representing all three chromogenic colours (cyan, magenta and yellow) was synthesised, and upon treatment of these dyes with aqueous acid, all three colours gradually degrade over time. Yellow photodyes require significantly less acid for noticeable degradation however, and magenta was generally the most stable, in line with observations on Russian Diplomacy. More detailed investigations revealed that the quenching of these dyes actually consists of two distinct processes, a fast, reversible protonation and a slower, irreversible hydrolysis. The acids present in this and similar artworks hydrolyse dyes in the photographic gelatine, causing a discolouration towards purple tones as found on Russian Diplomacy, while at the same time causing efflorescence formation from the superimposed alkyd-based varnish. These results underline the importance of a thorough intake procedure and regular monitoring of these artworks, in order to predict future degradation and apply proper precautions.