William Minter and John Baty presented the results of this aging study of particular relevance to those of us working with archives and library materials. The hypothesis: “Encapsulated acidic sheets will degrade faster than unencapsulated sheets”. The question driving the testing was whether deterioration products from the paper can become trapped in the encapsulation, thereby accelerating further damage. In essence, do encapsulated papers “stew in their own juices”? I, for one, certainly would have assumed the answer to be “yes”. But the use of encapsulation as a means of support for brittle and fragile documents beats lamination with cellulose acetate, as would have been the practice decades ago. What else is a paper conservator to do?
Here is how this study proceeded: Minter and Baty acquired different naturally aged papers for use in this study of the effect of sealing papers between film. The papers were typical of those in archives, including bond paper, ledger paper and “onion skin”. All were acidic prior to oven aging. To more accurately mimic natural aging, the temperature used during aging was 45°C instead of the more commonly used 60°C and papers were heated for a longer period of time than normal. The aging “oven” was a sealed glass box with a circulating fan, heating element (pad?), and saturated salt solution that maintained a moderate relative humidity. If you have never been in the market for an official accelerated aging oven, you may be surprised to learn that they cost a pretty penny; we’re talking 10k! Fortunately, this alternative oven was significantly cheaper, and performed very well, consistently maintaining both temperature and RH.
The primary method of checking the papers’ deterioration was by measuring degree of polymerization with size exclusion chromatography. Shorter hemicellulose chains in paper samples after aging equate to loss of strength and flexibility in the paper, properties that were also measured and evaluated with fold endurance and surface pH. Results showed that the encapsulated samples DID NOT age faster than the unencapsulated samples, contrary to the hypothesis! (Maybe some of you will sleep better at night having learned this fact?) I believe this test concluded after 33 weeks. If appropriate, It would be interesting to learn if an even longer aging period would yield the same result.
A second set of aging tests with the same papers revealed that either washing in magnesium carbonate or using a non-aqueous spray deacidification product prior to encapsulation would be equally protective of some papers. It is not known how long this protection would last, however.
This was a very relevant study, the importance of which can be well appreciated by many in the field of archives and paper conservation. A repeat study of a broader range of papers, (maybe photographic?) could also yield very interesting results. For me, this is an essential paper to file under “must read, and read again”.
AIC 41st Annual Meeting – Research and Technical Studies Session, June 1, "The Role of Polyester Film Encapsulation – With and Without Prior Deacidification – On Paper Degradation by William Minter and John W. Baty"
