4 CONCLUSIONS

Several conclusions about the blistering of paper from aqueous hydrogen peroxide bleaching can be drawn:

1. The more degraded paper found in the margins of these prints was more prone to blistering than paper taken from the rest of the sheets. This may have occurred because the marginal paper contained more catalysts for decomposition, perhaps as a result of handling, or possibly since this paper was weaker it was more susceptible to mechanical deformation.17 Unfortunately, it is generally the more degraded papers which are more disfigured by staining and discoloration and which could be more visually improved by bleaching.
2. Peforming a calcium hydroxide pretreatment wash or adding stabilizers to the bleaching bath may reduce the blistering somewhat, but this did not consistently cause significant reductions in blistering with the papers which were used in this study. Additionally, undissolved chemicals in the stabilized bath may interfere with the inspection of artwork during bleaching.
3. Using a less vigorous bleaching solution, as would be obtained by lowering the pH, seems to lessen the possibility of severe damage. Although less bleaching occurred during a fixed period of time, it would be interesting to see whether a comparable amount of bleaching might not occur if the bleaching time were extended.
4. Lowering the concentration of hydrogen peroxide seems also to reduce the amount of blistering, although perhaps not as consistently as does lowering the pH.
5. The addition of ethanol reduced the blistering quite well with most, but not all, of the papers studied. The amount of bleaching was also reduced. The results were fairly similar to those produced by lowering the pH form 10 to 9.
6. Caution is advised when drawing conclusions about hydrogen peroxide bleaching based on behavior observed with one particular paper. Quantitatively, the responses of the seven different papers in this experiment to the same treatment modifications were surprisingly varied.