5 CONCLUSIONS

1. Exposure to light, per se, during aqueous light bleaching in either Mg(HCO3)2 or Ca(OH)2 did not have a deleterious effect on the α-cellulose papers used in this study.
2. The two immersion solutions appear, on the basis of these experiments, to be equally effective for reduction of natural discoloration in the cellulose fiber furnish itself. Color reversion upon artificial, humid oven aging may be slightly less for samples bleached in Ca(OH)2; more experimentation would be required to confirm this possibility.
3. When aqueously light bleached in Mg(HCO3)2, the gelatin-sized artists' paper appeared slightly less yellow than when bleached in Ca(OH)2. The maximum stress that it could withstand was also less. These effects might be due at least in part to other factors, such as partial removal of gelatin size, which are not directly related to exposure of the paper to light.
4. The results reported above could not provide a resolution to the long-standing debate over the relative efficacies of Mg(HCO3)2 and Ca(OH)2 solutions used for bathing and deacidification.
5. Conservators wishing to choose between Mg(HCO3)2 and Ca(OH)2 bathing solutions for an aqueous light bleaching treatment will need to consider the many effects—in addition to exposure to light—that occur when the object is immersed in these solutions.