EFFECTS OF DILUTE CALCIUM WASHING TREATMENTS ON PAPER
JOHN BOGAARD, & PAUL M. WHITMORE
The use of dilute calcium solutions in water-washing treatments of paper sheets was examined through both accelerated thermal aging and light exposure and found to be generally beneficial. Risks of damage to the cellulose chain caused by these treatments, during both the immersion and the aging steps, were found to be small. Acid hydrolysis was determined to be the dominant degradation process in the thermal aging of treated sheets; therefore, the chemical stability depended more on the alkalinity of the treatment bath than on the presence of calcium. Eventually, the alkaline reserve imparted by these dilute treatments was exhausted, and the degradation rate increased. Papers that had been photo-oxidized were harder to stabilize than unoxidized sheets. For photo-oxidized cellulose, use of a sodium borohydride reduction treatment followed by an alkaline calcium wash gave the best result, in terms of retaining both cellulose DP and brightness. Papers treated with calcium hydroxide showed a slower rate of photo-oxidation when exposed to near-ultraviolet light than both un-treated sheets and those treated with calcium chloride.
It should be emphasized that this study examined the chemical interactions of calcium solutions with cellulose alone and did not look at interactions with sizing, coatings, or fillers that are commonly found in commercial papers. Nor were the effects on inks or artistic media, or the physical or aesthetic changes that can occur during treatment, examined. The paper conservator's experience still must be the guide to the use of the solutions on artifacts.