Examination and Dry Cleaning
Close visual examination suggested the heavy surface soiling was sooty in nature; the particles were black, powdery, and surrounded by light brown colored halos, possibly created by contaminants in the carbon-based soot. Plain water washing seemed unlikely to adequately reduce the extensive and varied staining.
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EnlargeDetail of sooty soiling with light brown halo stains, before treatment in normal light.
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Detail of same area with light brown halo stains, before treatment in ultraviolet light. Blue = stains that absorb UV; red = stains that fluoresce yellow under UV; black = stains that fluoresce orange under UV. Just below the red circle there is another stain weakly fluorescing orange, which appears slighly different from the stain in the black circle.
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EnlargeRaking light illumination, before treatment. Besides the heavy surface soiling and staining, the weak paper support had planar deformations, cracks, tears, creases, and losses.
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EnlargeDry cleaning started with low suction vacuuming through a screen to protect the brittle paper. The left side has not been vacuumed yet. After vacuuming, further dry cleaning was done with polyurethane sponges and ground plastic erasers.
Testing and Washing
Adjusting the bath water with the addition of chelators to remove otherwise insoluble metal salts, and buffers to maintain the pH of the bath, can improve the effectiveness of a washing treatment.
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The print ready for spot testing, after dry surface cleaning. A printout of the before treatment photograph lies to the left.
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A small plug of 4% agarose gel (prepared only with deionized water) sits on the surface of the paper (inset image) and pulls out ions through capillary action. Blank plugs were placed on both stained and unstained areas, providing an average measurement of the conductivity and pH of the paper.
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4% agarose plugs prepared with different washing solutions were then applied to various stains to observe which washing solution was most effective at reducing the stains. The eight test sites in this area are clearly visible as brighter spots in the paper.
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Detail of same area, after blotter washing with the chosen solution (containing citric acid functioning as a weak chelator and tetrasodium borate as a buffer).
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A similar stain in the image area (as opposed to in the margin), before washing (after dry cleaning) on the left and after blotter washing on the right.
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After blotter washing, persistent stains were treated with local applications of a 4% agarose gel made with a different washing solution (containing the stronger chelator diethylenetriaminepentaacetic acid and tetrasodium borate as a buffer), followed by screen washing with deionized water adjusted to pH 7.5 with saturated calcium hydroxide.
Mending and Matting
Treatment aimed to improve the legibility of the image and to strengthen the weak and brittle paper. Treatment stopped short of attempting to achieve an overall even paper tone.
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Left: verso detail, before filling. Right, verso detail, after filling with toned paper pulp, adhered with 2% methyl cellulose. Breaks and tears (not shown) were mended with acrylic-toned Japanese tissue adhered with wheat starch paste.
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After treatment. Treatment aimed to render the image area cleanly legible, without significant visual disturbance from staining. For example, to adequately reduce the large, distracting stain in the sky, limited light bleaching was still necessary after local gel treatment, but stopped well short of attempting to further minimize stains in the margins of the paper, since these could be matted out.
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After treatment. This is the same image as before, but cropped to show how matting can change, for the better, the overall appearance of uniformity in the paper tone.
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After treatment. This is again the same image, but showing how manipulating just the mat opening can further improve the overall appearance of uniformity in the paper tone. This mat opening is smaller (matting out the title below the print image), which eliminates the contrast between the less and more stained areas that were visible in the bottom right corner of the previous image. The optical effect is that this mat opening makes the print look cleanest and brightest of the three identical images.
