A STUDY OF THE PRESERVATION AND RESTORATION OF HISTORIC PHOTOGRAPHS AT THE NATIONAL ARCHIVES*

SAKDA SIRIPANT

ABSTRACT: A full scale investigation was undertaken into the nature and causes of deterioration of plates and prints which had been stored for about 100 years in the hot and humid Throne Hall in Bangkok's National Museum. The early glass plates and prints were stored in teakwood boxes. They had developed yellow and brown stains and some of them had faded from black to yellow. The stained and faded images were partly caused by oxidising gases released from teakwood boxes. The presence of oxidising gases in the box was confirmed by an experiment with the help of the Agfa yellow test film, which showed that the yellow and brown stains were composed of soluble silver salts. The envelope, cream-colour mounting board, brown paper board and Sa-papert were tested for acidity and alkalinity andfound to have pH 5.8, 5.0, 7.15 and 7.3 respectively. A newly developed method was used to make quality modem prints from extremely high contrast negative plates by overexposing the grade 1 paper for 10 times the normal exposure and then bleaching them in a 0.4% (by wt.) potassium dichromate solution for 60 seconds prior to normal developing and fIxing. The resulting scale index became 2.21. Plates and prints having overall yellow image were restored by photographing them on a blue sensitive film. The details of the faded image were enhanced by producing a highlight mask which was registered to negative when producing the final print. The restored photographic images were satisfactory.

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Department of Photographic Science and Printing Technology, Faculty of Science, Chulalongkom University, Bangkok 10500, Thailand

Received 17 December 1985