It’s probably safe to say that most book conservators have encountered at least one oil-stained textblock. In many cases, the source of the oil was leather dressing, historically applied in an attempt to improve the suppleness, appearance, and longevity of leather bindings. Many different formulae of leather dressing have been documented, but one of the best known is a roughly 1:1 mixture of neatsfoot oil and lanolin.
Treating this staining is challenging for a number of reasons: while conservators can speculate about the type and age of the oil causing the stain, they can’t always make a definitive identification, so extensive testing is often necessary; oil-based printing inks can be susceptible to the same solvents that will act on the stain; treatment of any stain in a bound textblock is difficult; and finally, depending on the amount of oil still saturating the binding, there is the potential for the stain to return or expand over time.
Holly Herro, Conservation Librarian for the History of Medicine Division at the National Library of Medicine presented on the development of a process to remove oil stains from book paper. The project was carried out in collaboration with paintings conservator Scott Nolley, Chief Conservator at Fine Art Conservation of Virginia, and paper conservator Wendy Cowan of Richmond Conservators of Works on Paper. Tests were conducted on a blank modern paper endsheet from a 15th century book. The sheet was stained with what the conservators suspected was a combination of neatsfoot oil and lanolin, applied approximately 30-40 years ago. Several protocols were tested, but the most successful at reducing the staining was as follows:
Pre-wash the affected page in a 50/50 solution of deionized water and ethanol buffered to pH 9 with ammonium hydroxide. In the tests, the samples were washed in three baths totaling one hour and air dried. Using suction, first apply a pipette filled with petroleum ether, a low polarity solvent that solubilizes the lanolin. Then apply acetone with a pipette, a high polarity solvent, to solubilize the neatsfoot oil. Continue alternating these solvents in a 1:1 ratio, changing the blotters regularly, until the oil is visibly reduced. Periodically view the substrate using a ultraviolet light checking for any oil residue. After the oil is reduced, wash the paper in a deionized water buffered to pH 9 with ammonium hydroxide.
The samples were examined under UV and visible light before and after treatment to determine the effectiveness of each treatment. The alternation of a polar and non-polar solvent over a suction table seems to have been an effective way to reduce both suspected components of the stain. The protocol was also tested on an endsheet in a bound book using a suction platen.
Leather dressing stains in books continue to be a common problem faced by book conservators and additional tips and tricks are always useful to have on hand. A great next step for this work would be testing of the impact of the protocol on printing inks.
To read more about the project and about techniques for reducing oil and leather dressing staining on paper, consult the following resources:
“Oil on Paper: A Collaborative Conservation Challenge” by Kristi Wright and Holly Herro: https://circulatingnow.nlm.nih.gov/2015/06/16/oil-on-paper-a-collaborative-conservation-challenge/
“Treatment Options for Oil Stains on Paper” by Denise Stockman: http://cool.conservation-us.org/coolaic/sg/bpg/annual/v26/bp26-22.pdf
“The Removal of Leather Dressing from Paper” by Brenna Campbell: http://cool.conservation-us.org/coolaic/sg/bpg/annual/v28/bp28-22.pdf