PMG Washing, Bleaching and Stain Reduction

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Photographic Materials Conservation Catalog
Chapter: Washing, Bleaching and Stain Reduction

Date: Initiated 2015
Contributors: Luisa Casella

The Photographic Materials Conservation Catalog is produced by the Photographic Materials Group of the American Institute for Conservation of Historic and Artistic Works as a convenience for the membership. The treatments, methods, or techniques described herein are provided for informational purposes. The reader assumes responsibility for any application results.

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.

Techniques

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).

Setup for bleaching with metal halide lamps. Image: Rachel Wetzel


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

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

References

Washing

Bleaching

Stain Reduction

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