A report on foxing and related phenomena appeared recently in the German language (Restauro, 1989, no. 3, p. 225-233) and in Dutch (De Restaurator, 1989, no. 1), and was also noted briefly in the October issue of this newsletter. The title in English is "Foxing Stains and Discoloration of Leaf Margins and Paper Surrounding Printing Ink: Coherent Phenomena in Books." The authors are Frank J. Ligterink, Henk J. Porck and Win J. Th. Smit.
The English summary is reprinted here (unfortunately without the excellent photographs) by permission of the authors and the publisher of De Restaurator. The address for correspondence (H.J. Porck and W.J.Th. Smit) is: Conservation Department, Royal Library, P0 Box 90407, 2509 LK The Hague, The Netherlands.
Though certain fungi and metal residues are proposed as factors which play a role in the development of brownish stains in paper, the published results of research in this respect are not completely convincing and, moreover, do not offer an overall explanation for the whole range of spotty discoloration symptoms encountered in books. As a consequence, the term generally used for these stains, foxing, is not yet unambiguously defined, and many questions with regard to the actual source and development of these discolorations still remain to be answered. In order to obtain more insight into this problem, we intensively studied a large number of different stains and other paper discolorations in nearly one hundred books.
Firstly we focussed on a frequently occurring form, namely the browning of paper around the printing ink. Our survey has shown that this so-called textblock discoloration very often appears in combination with browning of the margins of leaves and with foxing stains. Though according to the present views there is no relation between these different forms of discoloration in paper, our observations have clearly indicated that they are in fact all part of one complex phenomenon. Foxing stains appear to have developed at non-arbitrary places in the paper, often concentrated at
the leaf margins and in the textblocks, and can also join together to more or less homogeneously discolored zones. On the basis of this coherency and other similar characteristics, we propose to abandon the restriction of the term foxing to stains, and to extend its definition to the other more zonal forms of discoloration.
In connection with our discovery that sometimes a certain stain pattern which does not copy on the subsequent page, appears to repeat on pages further in the book, we reconstructed the original unfolded gatherings of the book in question with the aid of photocopies. This revealed that several stain patterns of successive gatherings corresponded when the unfolded sheets were put on top of each other consecutively. This clearly indicates that these stains originated during the storage of the unfolded gatherings, i.e. before the binding of the book.
Subsequently we performed a more detailed examination of the course of stains from page to page in several books. Our findings in this respect suggest that many stains are part of small or more extended three-dimensional structures inside the book, the stain pattern on each page being a cross-section of these structures. Evidently these stains have developed in the book after binding.
A third group could be distinguished, namely stains which repeat neither on the subsequent pages nor on pages further in the book. Presumably these stains originated in an earlier step in the book production process, possibly during the storage of identical, not yet ordered gatherings. In these cases, corresponding stain patterns can theoretically be expected in different books from the same edition. It was indeed possible to find two books which showed such a correspondence.
Though it now seems possible to elucidate the origin of stains in books by reconstruction of the original spatial stain structures, one has to deal with a complex situation where the various stains on one page may have originated in different steps in the book production process and thus will be part of different structures. Moreover, the use of more than one type of paper in the production of a book appears to cause sudden changes in the stain structures present.
As the present theories on the causes of foxing (fungi, metals) do not satisfactorily explain the observed relationship between stains and other forms of paper discoloration, another approach is needed. As already suggested by others, the physico-chemical process underlying the observed browning of humidified fibrous materials at the dry-wet interface might play a crucial role in the discoloration of paper. We presume that this browning reaction takes place in paper at accumulations of moisture, caused by local condensation processes in the book. It can be expected that many factors influencing condensation and evaporation will play a role in this respect. Additional research is planned to verify the condensation theory experimentally.