Conservation treatments of individual papers often include steps of washing with aqueous solutions.  Calcium salts may be added to the water to prevent removal of beneficial components and to aid in stabilizing the paper.  However, it has not been clear which calcium salt is most effective at stabilizing deteriorated and possibly oxidized papers as well as determining whether there are chemical side effects from these treatments which should be avoided.  Currently, we are comparing the use of a variety of calcium salts, evaluating their effectiveness in slowing deterioration in treated papers, and assessing the possible risks of this type of treatment.

The research focuses on:

• Washing paper samples with dilute solutions of calcium hydroxide, bicarbonate, and chloride, which cover a range of alkalinity.

• Monitoring samples exposed to accelerated thermal aging and light exposure after treatment with calcium salts.

• Evaluating the use of sodium borohydride, a reducing agent, to stabilize the oxidized sites on the cellulose chain prior to a calcium wash treatment.

The use of dilute calcium solutions was found to be generally beneficial at slowing the degradation of cellulose fibers.  Acid hydrolysis was determined to be the dominant degradation pathway in thermally aged sheets, and therefore chemical stability was dependent on the alkalinity more than the presence of calcium.  Papers that had been oxidized were harder to stabilize than unoxidized sheets when treated with the calcium salts.  It was also found that papers treated with dilute calcium hydroxide photo-oxidized more slowly.  Treatment using a combination of the sodium borohydride followed by a calcium hydroxide rinse imparted the greatest stability, but the conservator should be cautious about possible interactions with the ink, medium, or other paper components in such a treatment.

For more information:
            Bogaard et al. JAIC, 40 (2001): pgs. 105-123. (Abstract) (pdf [1.0 MB])