THE LIGHT BLEACHING OF DISCOLORED FILMS OF AN ACRYLIC ARTISTS' MEDIUM
| Main Authors: | , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0039-3630 |
| Online Access: | http://www.viks.sk/chk/studcon_4_02_228_236.doc |
| Abstract: | SUMARRIES. Films of Liquitex gloss medium on gesso that had been discolored either by dark storage of the original product or from addition of colored matter extracted from linen canvas were bleached by brief exposure to high-intensity visible light. After 20 hours of exposure to a UV-filtered xenon lamp, an exposure dose equivalent to four days under UV-filtered daylight fluorescent lights, the intrinsic yellow color of the naturally-aged films (initial Yellow Index of 23) was found to bleach significantly (about 40% of the original color remained after bleaching). For films that were discolored from material extracted from linen canvas (initial Yellow Index of 37), only a small fraction of the yellow discoloration was bleached in the exposure (about 70% of the original color remained after bleaching\\\}. The bleaching of the discolored films was not linear with light dose, and during the exposure of both the intrinsically discolored and canvas-discolored films the color decreased rapidly at first and more slowly as the bleaching proceeded. In subsequent dark storage of the bleached films, the original levels of discoloration returned. However, when bleached films were subsequently exposed to periodic, moderate light levels simulating gallery conditions, the films retained much of the improved appearance that had been gained from the bleaching treatment. CONCLUSION. The results of this study confirm the earlier observations of Levison [4] and those reported in prior work by the authors [1] that, like oil media, films of acrylic artists" paint medium tend to yellow in the dark and to bleach from light exposure. The light exposure conditions studied here were intended to probe the effects of a conservation treatment, and the results indicated that such a treatment promised significant improvement only for films that were suffering a moderate level of intrinsic yellowing (an initial Yellow Index of 23). Those films that were stained yellow due to their incorporation of colored matter from a support such as linen canvas (to a Yellow Index of 37) were more resistant to light bleaching, and the slight improvement in appearance for such canvas-induced discoloration may be deemed inadequate to warrant such treatment. Because of the kinetic behavior of the bleaching process, which sees progressively smaller changes for increasing doses, significant improvements on these results might require substantially greater light exposure times or more intense light sources, both of which incur greater difficulty and attendant risks. If light bleaching is considered as a treatment, the display of the bleached artifact seems the only sensible means to maintain the bleached appearance: the acrylic medium, like other materials such as paper and oil paints, returns to nearly its original yellowed condition upon dark storage. Of course, no light bleaching treatment should be performed without due consideration of the risks to colorants or other light-sensitive materials that might be adversely affected by exposure to these doses of visible light. It remains to be seen whether acrylic media films on artifacts that are on constant display will yellow to a level that warrants consideration of bleaching treatments. The results observed in this study, coupled with Levison's observations for high-intensity light exposures [4], suggest that ambient lighting in a gallery setting might be sufficient to prevent significant intrinsic discoloration of acrylic media films. The prospects for this will be examined in future work. |
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| ISSN: | ISSN 0039-3630 |
