PAINTINGS ON A PHOTOGRAPHIC BASE
7 EXAMINATION AND CONSERVATION
QUITE OFTEN, THESE PAINTED portraits are difficult to recognize because the photo image cannot be easily detected, being hidden by the paint film. Careful examination under magnification is required, especially in areas of the face, in details of the eyes, nose, mouth and the hands. The subtle gradations produced by the grains of silver in the emulsion or collodion or albumen of these regions allowed the artist to apply only a thin glaze of color. Otherwise the modelling would be lost. Other sections, such as costume, details of the clothing and background permitted the artist to use thick paint and the opportunity to improvise the colour arrangement. The staff artist would need to be present in the studio at the time that the sitter was having the photo taken in order to observe the coloring of his client's features and clothing for an accurate likeness, or details would be noted for the artist's information later if he were not present.
The attempts to confirm the presence of a photo image under a paint layer by means of radiography, Infra-red Vidcon or x-ray energy spectrometry (EDX) have not been successful to date; usually the overlying pigment tends to screen out the silver grains. However, presence of a paper support lying over a canvas should immediately alert the conservator to make a careful search along the marginal regions for some trace of a silver image. Examination under the binocular microscope so far seems to be the best method for seeking the presence of silver grains. Any surface accretion or discoloration should be treated with extreme caution. Solvent tests should be made first with absorbent cotton on small applicator sticks slightly moistened with diluted mild detergent at a place which lies under the frame rabbet. All that may be possible would be to remove surface soil only, because any coatings usually are extremely fragile, being a combination of a resin and pigment in the form of a glaze overlying a film of water-soluble gum arabic. In some instances, a coating of megilp, a mixture of dammar resin and boiled linseed oil, may be present. Megilp is known to become discolored in a short period of time and turn brittle, causing a network of craquelure promoting seepage by capillary action to lower layers of any solvent that may be introduced on the surface. In the case of watercolor over a silver image, the problem is reduced as the work is usually protected by glass. Should foxing or water stains be present, conservation treatment would proceed in the manner for works of art on paper.