2.14 Aqueous Light Bleaching of Paper

Los Angeles County Museum of Art
The Getty Conservation Institute

Terry Trosper Schaeffer
Victoria Blyth-Hill
James R. Druzik
Period of Activity: 8/91 to 11/96

Project Abstract
This collaborative project between LACMA and the GCI will undertake to provide a detailed description of the effects of aqueous light bleaching on the changes in paper properties caused by subsequent aging. In particular, attention will be given to rag paper samples which have been preaged under conditions chosen to create degradation typical of that faced by conservators. The effects of aqueous light bleaching will be monitored by measurement of gross chemical alterations in paper components and of changes in color and strength of the sample papers, after control and experimental treatments, and after posttreatment artificial aging.

Treatment conditions for the aqueous light bleaching step will closely parallel those used by practicing conservators. Initially, experiments will be performed to determine how variations in some experimental conditions influence the results of the treatment. Conditions which optimize results will be selected for use in subsequent studies, for which they will be carefully controlled.

Primary Publications
Schaeffer, T.T., V. Blyth-Hill, and J.R. Druzik, "Aqueous Light Bleaching of Paper: Comparison of Calcium Hydroxide and Magnesium Bicarbonate Bathing Solutions," Journal of the American Institute for Conservation, Vol. 35, 1996, pp. 219-238.

ABSTRACT-The immediate and long-term effects of aqueously light bleaching both unsized and gelatin-sized cotton cellulose papers in either calcium hydroxide, Ca(OH)2, or magnesium bicarbonate, Mg(HCO3)2, solutions were investigated. After samples were treated by washing, bleaching, or control bathing in the dark, one-half of all samples was assessed. Appearance was analyzed by reflectance spectrometry, tensile behavior was observed using stress-strain measurements, and pH and gelatin content in the papers were measured with modified TAPPI standard measurement procedures. The results showed that exposure to light per se during the bleaching process did not adversely affect the properties of the papers. It appeared that aqueous light bleaching of the unsized paper was equally effective in either solution. The visible changes in appearance, as well as alterations in other properties of the gelatin-sized paper, were influenced by the partial removal of sizing upon immersion. Finally, a clear preference for calcium hydroxide or magnesium bicarbonate as the bathing solution for aqueous light bleaching was not suggested by the results of the limited number of experiments possible in this study. Thus the choice of immersion solution should be made on an individual basis.

Schaeffer, T.T., V. Blyth-Hill, and J. R. Druzik, "Aqueous Light Bleaching of Rag Paper: An Effective Tool for Stain Removal," The Paper Conservator, Vol. 21, 1997, pp. 1-14.

ABSTRACT-When conservators of art on paper in the United States find a bleaching procedure is necessary, they frequently choose aqueous light bleaching. Experiments and practical experience with this technique have shown that when it is applied to rag papers it is effective and can produce aesthetically pleasing results. The long term efficacy of overall aqueous light bleaching has now been investigated, for removal of stains due to contact of gelatin-sized papers with acidic, ligneous materials. Unstained controls and controls for the treatments were included. Bleaching was accomplished with daylight fluorescent tubes. One half of each sample was artificially aged. The aqueously light bleached sample in each group was the least discolored. The tensile properties of maximum strength, elongation to break, and stiffness were not adversely affected by exposure to light during treatment. Paper pH was similarly unaffected. Some gelatin size was removed from the papers during immersion for treatment, but the aqueously light bleached samples lost no more than the controls immersed in the dark. The aqueous light bleaching protocol followed in these experiments appears to reduce the stain effectively. The changes in other attributes tested were no different from changes caused by bathing in a slightly alkaline solution.

Schaeffer , T. T., "A Semiquantitative Assay, Based on the TAPPI Method, for Monitoring Changes in Gelatin Content of Paper Due to Treatment," Journal of the American Institute for Conservation, Vol. 34, 1995, pp. 95-105.

ABSTRACT- A standard qualitative assay for glue in paper (TAPPI T 504 om-84) was adapted for use as a semiquantitative colorimetric procedure to determine changes in the amount of gelatin size due to treatment. The modified method is described in detail. Cellulose, alum, and proteins that do not contain hydroxyproline do not interfere with this assay. It has been used to document changes in the gelatin content of modern rag papers due to washing, aqueous light bleaching, and enzyme treatment. The results indicate that a significant fraction of the gelatin size was removed by immersion of the papers in Mg(HCO3)2 bathing solution at room temperature. Paper conservators may want to consider this phenomenon as a factor when they plan aqueous treatments for paper-based objects.