WATER-STAINED CELLULOSICS: A LITERATURE REVIEW
BESIDES EXPLAINING the consequences of spotting cellulose with water, this literature could offer a foundation for the study of the problem of foxing. Speculation and published data provoke the question of whether certain types of the reported spotting and staining known as foxing are related in any way to the brown line reactions.
There has been extensive discussion of the brown spots occurring on paper, with most authorities attributing them either to iron accumulated in the paper during processing, or to fungal infection. Recent authors1, 12, 14 seem to favor the latter explanation.
Using fluorescence microscopy, Meynell and Newsam examined samples from eleven books and, although the books were not obviously mouldy, found some hyphae associated with the foxed areas. Like the brown in the experiments discussed above, such spots were acidic and fluorescent. While suggesting that the growth of mould was responsible for the reaction of the amino acid indicators at the fluorescing perimeter of the stains, the authors noted that growth occurred around the lesions, that it was remarkably sparse and slow, and that it had no apparent effect on the fibers or on the paper. They concluded that growth occurred on the size, or on the soiled page edges; and that it was slowed by environmental fluctuations or insufficient food. Rather surprisingly, they then suggested that the tissue paper beside an engraving foxes readily precisely because it is unsized, and tends to be damp and absorbent. The role of sizing on moisture sorbtion is not considered, nor is the possibility of a correlation between browning and unevenness of size application.
If, in damp conditions, the page edges become the air-cellulose-water interface, brown line studies would predict local damage. Spotting on the rest of the page might be a function of variation in sheet thickness, leading to uneven concentration of moisture and, in areas slowest to dry, browning. As Bogaty observed, mould grew preferentially in the brown line-damaged areas, suggesting that the observed growth might be a result of spotting rather than a cause.
Such a view is consistent with the findings of Cain and Miller,6 who distinguished five different classes of foxing. Two of the classes were studied, and one was persuasively attributed to the presence of iron particles. In the group designated class 2, it was found that the local iron content of one sample group was lower than that of the control, and that in another sample group, hyphae were associated with only one of three hundred sixty spots.
Given that class 2 spots are not yet firmly attributed to iron and that fungal activity is not solely responsible for spotting, the effect of fluctuating moisture content on a cellulose substrate of uneven thickness should be considered.