Sunday, June 19, 2016

Celluloid storage and acid absorption

As celluloid ages, it emits a range of compounds. Some are benign, but as the celluloid begins to approach its expiration date, some rather nasty stuff gets released -- most notably, nitric acid. This in turn accelerates the process of deterioration, as well as attacking other nearby materials. For this reason, conservators recommend storing celluloid artifacts separated from each other and with ventilation. Keeping the temperature and especially the humidity low also slows the aging process. (see Julie A. Reilly, "Celluloid Objects: Their Chemistry and Preservation", Journal of the American Institute for Conservation, 1991, vol. 30, no. 2, article 3, pp. 145-162).

The release of acidic compounds begins well before any visible signs of material degradation, as has been demonstrated by wrapping old celluloid pens in litmus paper. Litmus paper, however, is just an indicator. It doesn't do much of anything to absorb or neutralize free acids. For that, elementary chemistry suggests the use of a mild base, such as sodium bicarbonate (baking soda) or calcium carbonate (lime). Museum conservators have indeed used calcium carbonate to trap acid gases, but as it turns out, far better options are available.

For pen storage, the best choice seems to be SPZ-grade zeolite, and in particular, MicroChamber papers. These papers are impregnated with high-absorption zeolite with an alkaline buffer, and can be used to line pen storage areas or to wrap individual pens. Standard-sized interleaving paper costs under $0.25 per 6.5 x 10.125 inch sheet, and can be bought through Amazon or directly from the manufacturer. Studies going back over twenty years show that these acid-trapping papers outperform calcium carbonate dramatically, both in thoroughness of acid capture and neutralization, and in retaining the ability to trap and hold acids and other atmospheric pollutants over time (see Siegfried Rempel, "Zeolite Molecular Traps And Their Use In Preventative Conservation" (Western Association for Art Conservation Newsletter, January 1996), Getty Conservation Institute, "Performance of Pollutant Adsorbents (2001-2003)", and the Conservation Resources website). I now have MicroChamber paper lining most of my pen and parts storage areas, supplemented by silica gel canisters to absorb excess humidity. Though standard-sized paper is what I have, 14-inch paper is required if you want to pleat it around the dividing ridges of a standard 12-pen slotter box. Finally, I have no financial stake in any of these products -- I am using them because all the sources I could find indicate that they offer the best protection option (noting that activated carbon filters are of comparable merit, though much bulkier).

NOTE: There are MicroChamber papers that also incorporate activated carbon. And as a Facebook commenter noted, one can also place strips of MicroChamber paper *inside* celluloid pens for additional protection -- though if the pen is to be used regularly, the paper will have to be cut and shaped carefully so as not to interfere with the filling mechanism. The greatest benefits would be with button-fillers and other pens with barrels that are tightly sealed.


Unknown said...

David, what a thoroughly researched and brilliantly presented article. Thank you from me and every other celluloid fan who reads it. Anyone who has seen celluloid disintegrate and damage what's around it will understand. Those who have not, take heed. This is not mythical fantasy.

Derek-L said...

Yes. I echo Mario's comments. Thank you David.

David said...

Thanks for your kind words. If you find the information useful, please don't hesitate to share it.

Unknown said...

Any thoughts for how long the sheets last? For example, do you replace them every other year?

Thanks for posting. I've read many articles about all the things to worry about regarding celluloid, but very few concrete descriptions for things you can do.

David said...

From what I have read, the sheets are likely to retain their absorbent capacity for years. I do intend to follow up with the manufacturers to get more specific information, however, including how one might determine how much capacity remains. The one circumstance where I would change the sheets more frequently would be if they had been exposed to plastic that was in the throes of end-stage deterioration.

Daniel Novotny said...

Thank you for an excellent article. I would be interested to know what kind of effects, if any, are recorded or reported in users in regard to the vaporization and contact in everyday usage with celluloid pens that are in the process of off-gassing nitric acid. Similarly, what would be the effects on quality of the environment when storing a substantial collection of vintage Celluloid pens.