Oil on Paper: A Collaborative Conservation Challenge

By Kristi Wright and Holly Herro

Sometimes conservators encounter problems resulting from well-intended but ultimately flawed repair techniques.  One example of this is the formerly widespread practice of applying oil to the covers of books.  Once considered best practice in libraries, the application of oil-based leather dressing to leather book bindings was a widely accepted treatment method.  The idea was to keep the leather supple and prevent deterioration.

As was the case with many well-intended treatment methods, these leather “dressings” did not pass the test of time. In NLM collections, the oil ultimately absorbed not only into the leather, but also sometimes migrated into the paper pages and other adjacent porous materials.  In some cases this may be a result of overzealous application, but in other cases the oil is simply seeping through the leather cover and moving deeper into the book.

A photograph of an open book showing darkened areas where oil has soaked into the endpaper.

Oil saturated paper on Die Ordnung der Gesundheit

The Library staff at that time kept thorough item-level notes about the oiling process, so we know which books were oiled, when, how many applications occurred, and the formula used.  These documented applications happened between 30 and 40 years ago and primarily used a combination of neatsfoot oil and lanolin.  Not unique to the collections of NLM, this issue affects collections nationwide. When we began looking for a solution, we found that there was no known method for reversing this process and removing the oil from this paper.  None surfaced even after consulting with book conservators at several different institutions, though most of them confirmed having similarly affected collection items.

While investigating treatment options, NLM book conservator Holly Herro consulted a well-known Richmond-based paintings and objects conservator, Scott Nolley, Chief Conservator at Fine Art Conservation of Virginia.  Given the prevalence of lacquers and other coatings on paintings, she thought that he might have some insight into the best methods for removing the oil. Though he did not have an immediate solution, Scott was intrigued by the problem of oil embedded in paper. He and paper conservator Wendy Cowan of Richmond Conservators of Works on Paper joined forces to develop some treatment ideas.  They tested these ideas on a naturally aged oil-saturated modern endsheet from Practica, seu, Lilium medicinae, a 15th-century book in NLM’s collection.

After the series of tests, one treatment emerged as the most effective. It is a multi-step process that involves first washing the paper in an alkaline 50/50 deionized water and ethanol solution in order to prevent unsightly stains, called tidelines, from appearing during treatment.  Next, a suction table is used to pull alternating multiple applications of petroleum ether and acetone—solvents chosen for their different solubility properties—through the paper.  This process dissolved and mobilized the different components in the oil and, and applied in combination with the suction, reduces it from the paper. As a final step, the treated paper is washed again in alkaline deionized water to remove any residual water soluble discoloration. Using this method, the oil appears to be completely removed from the paper, verified by viewing it in both normal and ultraviolet light.

Scott and Wendy visited NLM to demonstrate the effectiveness of this treatment protocol and share ideas more generally across our specialties. We benefited from Scott and Wendy’s expertise in their respective conservation specialties and were able to apply that knowledge to book conservation in a unique way.   This cross-disciplinary collaboration was a great experience and has resulted in a new treatment technique that others can use to treat similar cases of oil-saturated paper.   Of course, no treatment can be used in every situation because there are a lot of factors to consider for each individual item.  However, we’re quite glad to have this option to explore when books with oil migration show up in the lab!

We would like to thank our colleagues and collaborators on this research, Scott Nolley, Chief Conservator at Fine Art Conservation of Virginia and Wendy Cowan of Richmond Conservators of Works on Paper.

Kristi Wright is a contract conservator for the Conservation Program of the History of Medicine Division at the National Library of Medicine and principal of Wright Conservation and Framing.

Holly Herro is Conservation Librarian for the History of Medicine Division at the National Library of Medicine.