PMG Washing, Bleaching and Stain Reduction
- 1 Purpose of Washing, Bleaching or Reducing Stains
- 2 Factors to Consider Before Washing, Bleaching or Reducing Stains
- 3 Techniques
- 3.1 Light Bleaching Overall
- 3.2 Chemical Bleaching Overall
- 3.3 Light and Chemical Bleaching
- 3.4 Localized Bleaching
- 3.5 Localized application of gellam gum for stain reduction
- 4 Guidelines and Recommendations
- 5 References
Purpose of Washing, Bleaching or Reducing Stains
Washing, bleaching and/ or stain reduction may be carried out to reduce discoloration on photographic materials.
Light bleaching is a fairly known practice among photograph conservators that has reportedly been more successful when applied to platinum prints than to albumen and silver gelatin (Wetzel, 2005). Many conservators opt not to use this technique due to considering that the risks outweigh the possible benefits and that not enough research has been done on the long-term effects of this treatment on photographic materials (Wetzel, 2005). Bibliography used for this entry is primarily focused on the effects of bleaching on the paper substrate of objects.
Factors to Consider Before Washing, Bleaching or Reducing Stains
Condition of the Object
It is crucial to assess the object’s condition and resiliency to undergo any of the possible stain reduction treatments.
Nature of the stains and/ or discoloration
It is relevant to identify as possible the nature of the discoloration product to be reduced and the likelihood of its reduction by available techniques.
Stains and discoloration may be a result of adverse environmental conditions; residual chemistry; environmental pollutants and/ or contact with poor quality materials; accidental damage.
Light Bleaching Overall
Light bleaching is carried out by exposing the wet object to intense white light, around 5000k color temperature. This can be done either by exposure to sunlight or using metal halide lamps, commonly used for indoor lamp growth (in her 2005 research, Rachel Wetzel used "HF Sunburst 250W MH AgroSun Gold Deluxe System with Sunrise Reflector Hanging System. The units themselves weigh about 30 pounds each and are comprised of metal reflectors with a sheet of tempered glass that contains the light bulb within the unit. The lamps hang from the ceiling and provide even light coverage for a 3 x 3 foot area with some additional coverage in a 5 x 5 foot area when place 16-20 inches above the tray of water" ). Wetzel replaced the original bulbs that came with the system (that were a combination metal halide with set up) with General Electric Multi-Vapor Metal Halide Bulbs (#42729 MVR250/U)). Ideally the spectral distribution of the metal halide bulb should contain peaks in the ultraviolet, blue-violet and blue range of the electromagnetic spectrum as well as peaks in the green and yellow range (Wetzel 2005).
With light bleaching, heat build up is a concern both with sunlight as with lamps and the temperature need to be closely monitored.
Time of treatment varies based on visual results, although paper support and and binder condition need to be closely observed for any change. Chemical bleaching in particular will weaken paper fibers.
Light bleaching overall using sunlight, having the object immersed in distilled water
Light bleaching overall using metal halide lamp source, having the object immersed in distilled water
Chemical Bleaching Overall
Chemical bleaching by immersion in water with hydrogen peroxide.
Light and Chemical Bleaching
Chemical bleaching by immersion using hydrogen peroxide in combination with sunlight
Chemical bleaching by immersion using hydrogen peroxide in combination with metal halide lamp
In her research, Rachel Wetzel used 8x10" plastic trays used for wet photography processing, filled with 1000ml of distilled water to which 10ml of distilled water with 3% stabilized hydrogen peroxide were added (Wetzel 2005).
Localized bleaching using hydrogen peroxide.
Localized application of gellam gum for stain reduction
Gellam gum has been successfully used to locally reduce stains in photograohic materials. Gellam gum can be used by itself, applied over a stain area, and staining agents are pulled out of the object onto the gellam gum by capillarity. In paper conservation, gellam gum has been also used in combination with solvents or bleaching agent applied with brush or dropper over the gellam gum while it is on top of the stained or discolored area.
Guidelines and Recommendations
- Messier, Paul, Vitale, Timothy. 1994. Effects of Aqueous Treatment on Albumen Photographs. JAIC Volume 33 Number 3. American Institute for Conservation. pp. 257 - 278. Available online at: http://cool.conservation-us.org/jaic/articles/jaic33-03-003_indx.html
- Perkinson, Roy. 2001. An Alternative Light Source for Light Bleaching in Paper Conservation. The Book and Paper Group Annual, 20. pp.27-30. Available online here: http://cool.conservation-us.org/coolaic/sg/bpg/annual/v20/bp20-08.pdf
- Messier, Paul, Baas, Valerie, Tafilowski, Diane, and Varga, Lauren. 2005. Optical Brightening Agents in Photographic Paper. JAIC Volume 44 Number 1. American Institute for Conservation. p. 1-12. Available here: http://cool.conservation-us.org/jaic/articles/jaic44-01-001_indx.html
- Schaeffer, Terry Trosper, Baker, Mary T., Blyth-Hill, Victoria, Van Der Reyden, Dianne. 1992. Effects of Aqueous Light Bleaching on the Subsequent Aging of Paper. JAIC Volume 31 Number 3. American Institute for Conservation. pp. 289-311. Available here: http://cool.conservation-us.org/jaic/articles/jaic31-03-003.html
- Wetzel, Rachel. 2005. An Examination of the Short and Long Term Effects of Light Bleaching Silver Gelatin Photographs. Capstone Project for the 4th Cycle Advanced Residency Program in Photograph Conservation. George Eastman House, Image Permanence Institute. Available here: http://notesonphotographs.org/images/1/10/LBEXPweb_for_web.pdf
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