Mycological and FTIR analysis of biotic foxing on paper substrates

The small rusty stains (foxing) frequently found on historic paper documents, books, and prints have generally been analysed in the past by optical microscope through their morphochromatic appearance under visible light and UV radiation. Despite increased research efforts with more sophisticated techniques (mainly SEM and XRF), the biotic or even chemical origin of these stains remains unclear. The purpose of this paper is to verify to what extent a simple technique such as FTIR-ATR spectroscopy can be utilised for a clearer understanding of the controversial nature of foxing. Since this technique is sensitive to several organic chemical groups that are in common with both fungi and gelatine-sized ancient paper, some modern cardboards stained by biotic foxing have been selected for the analyses. The results clearly show the importance of FTIR and mycological analyses for the identification of residual microfungal agents, together with the by-products of their activity on paper substrates.