Technical Examination for Photographic Materials
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Technical Photography and in particular UVF (Ultraviolet Fluorescence Photography) is widely used for Photographic materials examination for conservation. Photographic materials show a wide range of fluorescence phenomena. Strong fluorescence is due to organic materials such as in the albumen prints (strong whitish fluorescence), collodion, and gelatin printing-out papers. There are also plenty of optical brightening agents used in photographic supports. On the other hand, there are also materials used in color prints that absorb ultraviolet radiation and appear dark in UVR (Reflected Ultraviolet Photography).
Also, the same paper materials can show different fluorescence if aged differently, for example when the borders of a photo are exposed to much less amount of light due to a window mat. This is the case for example of tinted albumen prints which contains dyes caracterized by poor light fastness.
Technical Photography is also useful to detect retouching pigments and inks and to reveal coatings. UVF is effective in mapping the adhesives and in revealing foxing and molds. Overall, since most photographic materials have paper support, they are likely to show all the phenomena that are observed in paper conservation. such as mold and foxing. Consequently, UFV is used to check if mold has been effectively removed during a cleaning process. UVF is particularly valuable to detect mold and foxing which are not yet become visible to the naked eyes because once identified a specific preventive conservation plan can be devised to avoid their developing into visible stains.
Generally different kind of papers can exhibit varying fluorescence colors under UV radiation, but UVF cannot determine accurately their type since their actual fluorescence emission color could depend on a number of facts such the used pulp. sizing and bleaching, just to name some. On the other hand, we use UVF to localize paper repairs which usually look identical under visual inspection, but become apparent under ultraviolet radiation.
The same can be said for adhesives, they also show fluorescence, generally whitish or yellowish. Again, they cannot be accurately identified. They can be effectively mapped, so we can successfully use UVF, for example, to monitor the progress of an adhesive removal.
When the paper is not evenly wet, for example for a flood, tidelines become visible at the border between the dry and the wet areas. Tidelines generally exhibit UV fluorescence, sometimes even those that are not yet visible to naked eye.
Eventually, photographic materials could also have faded writing that can be revealed with UVF.
References C. Buzit Tragni “The Use of Ultraviolet-induced Visible Fluorescence for Examination of Photographs” A. W. Mellow Fellow, Advanced Residency Program in Photograph Conservation, Image Permanence Institute, 2005.