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Fungi in Fox Spots of a Drawing by Leon Wyczółkowski

Abstract Many authors dealing with the phenomenon of foxing on paper point out its microbiological origin, but in fact, foxing-causing fungi can rarely be cultured. Leon Wyczółkowski’s drawing “The Market in Gniew” is an exception in this respect: its paper carrier shows foxing as well as numerous hyphae and cleistothecia, visible to the naked eye either as a white and fluffy coating or as a light yellow powder. Our aim was to investigate their role in the formation of foxing. Microscopic observations revealed uncountable amounts of lenticular spores and spherical asci. Incubation of the yellowish powder on microbiological media enabled the isolation of five strains: Eurotium rubrum, E. repens, Aspergillus versicolor, Penicillium solitum, and Penicillium decumbens. Three of them secreted yellow-colored pigments to the culture media. The reproduction of foxing on test papers with the use of these strains was successful. Brown stains resembling foxing appeared on the samples of all four types of paper placed on 1-week-old colonies of Eurotium rubrum. E. repens and Aspergillus versicolor also resulted in the creation of such stains, but only on some types of paper. It was not possible to determine the source of nutrition of the fungi unequivocally.