The article discusses the study of foxing stains in papers from the 16th to 20th centuries in Portuguese collections. The authors found that iron impurities, moisture absorbency, and new papermaking processes played a role in foxing stain formation.
Visual observation and digital imaging were used to analyse selected batches of papers. Different paper types and historical periods showed varying degrees of foxing, with gelatine sizing and iron impurities being key factors. The presence of iron-containing impurities throughout the paper leaf was highlighted as a catalyst for the oxidation of cellulose, leading to foxing stains.
The study revealed that certain papers developed similar foxing stains due to specific characteristics like gelatine sizing quality and absorbency of moisture. UV imaging showed fluorescence in foxing stains, and treatment with calcium hydroxide reduced fungal activity.
The surveys conducted on three Portuguese institutions provided insights into the prevalence of foxing stains in different time periods. The article concludes that foxing remains a subject of discussion, with each study contributing to a better understanding of this phenomenon.
Overall, the research sheds light on the complex interplay of factors influencing foxing stains in historical papers, emphasising the importance of considering paper quality, impurities, and environmental conditions in the preservation of cultural heritage materials.
