Hindsight is 20/20: Revisiting Paper Treatments From Twenty Years Ago

This post is written in honor of Preservation Week, April 24–30, 2011. In celebration of this week, preservation specialists around the world will bring attention to the preservation work going on in their institutions, and inspire action to preserve collections in libraries, archives, museums, and communities. As a recipient of a 2010–2011 Post-Graduate Fellowship in Conservation, I came to the Smithsonian Institution Archives in September to research the treatment history of Record Unit 92: Prints and Drawings 1840-, a collection of several thousand architectural prints and drawings, most of them depicting Smithsonian buildings. Many of the drawings were executed by famous architectural firms and practitioners,  including Hornblower and Marshall, Cluss & Schulze, and James Renwick.  The drawings and prints vary widely in the ways they were  created. There are hand-drawn images on paper, tracing paper, and tracing cloth; some were executed in graphite, others in ink or colored crayons.  The collection also includes a variety of  photographic images reproduced  as gelatin photographs, diazotypes, blueprints (cyanotypes) and photostats. While some of the materials that were used to create these architectural drawings have remained  stable over time, others have proved to be more fragile and have inherent problems, including the fact that paper itself tends to become more acidic and more brittle over time. We have all seen old paperback books that have become brown and brittle with age and are falling apart into little chips of paper flakes instead of pages. Conservation treatments to combat the natural acidity of paper vary widely, and include procedures as non-invasive as rehousing documents or artifacts in alkaline folders to reduce their uptake of acids from the environment,  to treating them  with “dry” non-aqueous chemistry,  to  bathing them in alkaline water baths. In the late 1980s, some of the RU92 architectural drawings were sent to the Northeast Document Conservation Center (NEDCC) for treatment, and nearly one hundred of them were deacidified using either a water bath containing magnesium bicarbonate or a non-aqueous deacidification spray in common use at that time. Now, more than two decades later, I’ve measured the pH (a relative measure of acidity and alkalinity) and the background color for each drawing using specialized tools, and then compared those deacidified architectural drawings to similar, but untreated drawings in the collection as a control group. I’ve identified some interesting trends. As expected, the untreated drawings are acidic, with a measured pH between pH 4 and pH 6 (ph 7 is neutral). My readings for the treated drawings show that they tend to be less acidic and some are now quite alkaline. The pH of the drawings that were treated with magnesium bicarbonate ranges from 5.5 to 10, with an average pH around 7.5, which is just slightly more alkaline than neutral. The drawings that were treated with the non-aqueous deacidification spray have readings  as low as pH 4.5 and as high as pH 10. Some of the drawings were only sprayed on the back, which has interesting implications for future treatments of those drawings, because while the pH on the front side of one, for example, measures near pH 5, the reading of the back measures near pH 9. The scale for pH is a logarithmic, so the difference between those two readings is not really just four points apart, but reflects a 10,000-fold difference! When I measured the pH of the drawings, I didn’t take readings in  just one spot, but in five different places  across each of the drawings, in order to average differences due to handling, chemical application process, and environmental influences. Statistical analysis of those measurements shows that the vast majority of the untreated drawings were acidic, with readings between pH 4.4 and 6.4, while the drawings bathed in magnesium bicarbonate had a slightly larger range of variation, with the majority of measurements falling between pH 6.1 and 8.5. Most notably, the drawings treated with the non-aqueous spray showed  the largest range of difference of the  three groups, with the majority of measurements between pH 4.9 and 8.1. I am now in the process of writing up my data and conclusions for a presentation to the Archives and later plan to write more broadly about what the implications of these findings may suggest with regard to future deacidification projects.

Anna Friedman is the Post Graduate Fellow in Conservation at the Smithsonian Institution Archives.