A Chemical Comparison of Two Different Oxidizing Bleaches and the History of Early European Paper and Papermaking

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Davies, Michael Christopher
The Chemistry of Paper , Art Conservation , History of Technology , History of Paper , Art History , Papermaking , Art Conservation Science
Background: The bleaching of paper is an important and controversial treatment employed in the conservation of art. The use of a bleach may greatly enhance the quality of an image but at a cost of lost structural integrity. In order to fully consider the ramifications of bleaching a paper artifact, a historical study of early European paper and its manufacture was conducted. The structure of paper was also studied in order to understand the finer points of early European paper manufacture and to draw conclusions from the bleaching comparison. Results: A comparison of the commonly used ClO2 bleaching with a previously proposed chlorous acid treatment was conducted. The two different bleaching techniques were evaluated on their impact on the colour of artificially aged and unaged Whatman chromatography 1 paper. The results of the bleaching were analyzed with a colourimeter and it was determined that there was a significant change in colour as a result of the bleaching. The ClO2 and chlorous acid bleaching treatments did not produce results that were significantly different from one another, visually and statistically. The bleaching treatments were also tested with the viscometry of the paper in cadoxen and it was determined that ClO2 is a more degradative bleach than chlorous acid. The research also demonstrated that bleaching has a greater degradative impact on previously degraded samples. The quantitative results of the viscometry were accompanied by a qualitative look at the paper samples with a scanning electron microscope (SEM). In the SEM images there were slight visible differences in the samples that could correlate to aging. Conclusions: Chlorous acid is a gentle effective bleaching technique that was as effective as ClO2 and less degrading to the paper samples. Bleaching has an increased impact on previously degraded samples, and conservators should be wary of this. Further research involving this bleaching technique is suggested. The use of an SEM in imaging damage to paper is a viable option but more work is needed with this technique to ensure conclusive results.
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