Restoration and preservation of severely embrittled and curled historical photographs by glycerol triglycidyl ether emulsion

Historical photographs are an important category of cultural heritage and present a wealth of historical information. Unfortunately, these photographs are suffering from brittle curling, folding, and fracturing diseases, the previous strategies can correct mildly curled photographs but are inapplicable to severely brittle and extensively curled photographs. This study developed a new method based on the synergistic effects of the molecular plasticisation, cross-linking, and shaping of glycerol triglycidyl ether (GTE) to toughen, flatten, and restore embrittled and curled historical photographs. First, the effects of GTE treatment on the shrinkage and curl resistance of gelatine-based photographic films were evaluated at the macro and micro levels under accelerated humid-heat ageing conditions. Next, spectrophotometry and MATLAB calculations were used to characterise the colour difference, surface light absorption, and grey value of photographs before and after GTE treatment. Comprehensive evaluation revealed that GTE treatment combined with traditional craft techniques could successfully realise the plasticisation, flattening, restoration, and conservation of severely curled historical photographs. A storage apparatus for keeping the restored historical photographs was also devised. This study focuses on a typical practical case for the restoration, conservation, and durable preservation of curled gelatine-based historical photographs and offers theoretical and technical support for the conservation of these valuable historical artefacts.