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From George Eastman House : Notes On Photographs

Return to the Lexicon for Photograph Deterioration defines and illustrates Mechanical, Chemical, and Biological and Environmental Deterioration.

Silver-mirroring, edges

Over time some air pollutants (in the presence of moisture and heat) can create a sustained migration of silver ions in all directions. When these silver ions reach the print surface, they form a reflective layer of silver, commonly referred to as mirroring or silver-mirroring. It is most easily seen when the print is examined in specular light, and it appears as a highly reflective sheen with a bluish cast. Mirroring only occurs in the shadow areas of the print where there is sufficient silver, which can be clearly seen in the print by Alfred Stieglitz, shown here in both standard lighting (Figure 35) and specular lighting (Figure 36).

Figure 35. Alfred Stieglitz, Lake George, ca. 1930

Figure 36. Alfred Stieglitz, Lake George, ca. 1930. The silver-mir¬roring is emphasized in this photograph by the use of specular lighting. (Courtesy George Eastman House, Acc. No. 1974.0052.0033))

When silver-mirroring forms preferentially along the edges, it indicates that air pollutants play a role in the oxidation of the silver. The mirroring then moves slowly inward, creating a halo-like effect around the center of the image (Figure 37). Be aware that mirroring, though often a good indicator that a print is at least 20 or 30 years old, can also be removed from a print, as described in Sidebar 6, or even added.

Mirroring along the edges caused by air pollutants can be mimicked by a poor-quality window mat (P3). It has been observed that mirroring often does not occur on poorly processed prints. The sulfur from the residual fixer combines with the silver ions to form stable silver sulfide before the silver can travel all the way to the surface.

Silver-mirroring is closely related to yellow/brown discoloration and fading (P4–6). When the same oxidation and migration of silver that produces silver-mirroring in the shadows occurs in the midtones and highlights, the result is fading and or warming of the image, depending on the size, density, and composition of the resulting silver particles. This can be clearly seen, for example, in Figure 36.

Silver-mirroring, overall or localized

While fully purified wood pulp is harmless to photographs, and in fact has been used for photographic paper base since the 1920s, paper and boards made from wood pulp (from which the non-cellulose components have not been fully removed) can cause staining of the gelatin and image silver degradation. Such unpurified wood pulp contains lignins and other extractives, which may cause silver-mirroring when left in proximity to a gelatin silver print. Paper materials that often use this wood pulp include newsprint, grayboard, and cardboard.

Image silver degradation can occur locally or overall depending on the size and shape of the offending material and its contact with the print. If the poor-quality core of a matboard is exposed to the print only along the edges, it can result in edge mirroring, mimicking the effect of air pollutants, as discussed in Pathway 2. If overall contact occurs with a poor-quality paper then mirroring will appear overall in the shadows (Figure 39).

Figure 39. A gelatin silver print from Albert Mebes’ 1913 Der Bromsilber- und Gaslichtpapier-Druck. Overall silver-mirroring has resulted from contact with the book’s paper that contains unpurified wood pulp.

Gelatin staining caused by paper materials made with unpurified wood pulp is discussed in Pathway 7.