PMG Releasing, Detaching, and Separating

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In progress: Seeking additional comments and images to develop this section


Date: Initiated March 2020
Contributors: Stephanie Watkins, Barbara Lemmen, Michelle Sullivan (gels),

The Photographic Materials Conservation Catalog is written by members of 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. Best professional judgement is necessary when using or interpreting this provided information. The reader assumes responsibility for any application results.

Purpose of Releasing, Detaching, and Separating

  • Many types of photographic materials, but often gelatin based ones, can become attached to each other in a stack, to adjacent papers whether in a book or stack, or to glazing, often to glass, while in a frame. This section addresses various methods and materials for releasing these attachments.
  • This section does not cover overall unmounting [[1]] of photographs.
  • Some photographic material is intentionally adhered to other materials, as are face-mounted photographs. Treatments aimed at separating intentionally adhered photographic materials are not covered in this section.

Blocked Photographs and Negatives

Photographs and negatives can become "stuck" to other photographs, paper, or glazing (glass or acrylic). It is common for loose photographs and negatives, such as silver gelatin developing out processes, some Polaroid processes or others with a coating or adhesive on their surfaces, to become adhered to each other while in a stack or to glazing materials while framed if the humidity is high enough or a water event occurs. This process is called "blocking".

Why Materials Get Stuck

  • Image and binder layers may swell and increase tack in the presence of moisture (humidity or water).
  • Heat may also cause attachment to adjacent materials.
  • Pressure (light, but constant) may cause attachment to adjacent materials in combination with moisture or heat.
  • Fungus (mold/conidia) may grow through the photographic material weakening it while "binding" the stack together.
  • Varnishes, coatings, and adhesives may be present on front, back or both sides of a photograph.

Attachment Mechanisms

  • Adhesion is the tendency of dissimilar particles or surfaces to cling to one another (from WIKIpedia)
  • Cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another (from WIKIpedia)
  • (Lemmen and?) Lowe (2016) investigated the mechanism of attachment specifically between:
    • Gelatin silver developed-out paper (DOP) photographs and picture glass
    • Gelatin silver developed-out paper (DOP) photographs and themselves in a stack (blocked)

The authors noted that because of the process of moisture and heat introduction, the gelatin layer is modified. If the gelatin swells above the glass transition temperature, the gelatin increases tackiness and can be rubbery (the gelatin becomes "adhesive"). If the photograph is positioned against another material, the two surfaces may attach. The attachment can be avoided if the photograph and adjacent material are separated while the gelatin is still moist and swollen.

    • Mechanical bonds can form between softened gelatin and paper.
    • Mechanical bonds can form between adjacent softened gelatin layers.
    • For blocked prints, the drier the gelatin becomes, the less likely clean separation will occur.
    • For glass and gelatin print attachments, the adhesion changes from electrostatic (single ion exchange between two atoms) to covalent bonding (ion pair sharing between two atoms) within a few months time.
    • Gelatin may more likely adhere to uncoated picture glass than various coated picture glass types (like those with UV coatings).

Factors to Consider

  • Adhered photographs cannot be used, nor appreciated, as the image content is unknown.
  • Not all attachments will release, or release cleanly.
    • The type of bond created between the gelatin and the adjacent surface dictates treatment success.
    • The type of photographic surface (glossy, matte, etc.) and the surface of the adjacent material affects the attachment strength.
    • The age of the material and length of attachment may affect separation attempts.
      • Weakly formed bonds may separate more easily during treatment.
      • Strongly formed bonds will likely sheer a paper support, leaving an island of photographic material adhered to the adjacent material.
  • Fibers, coatings, or image layer may remain attached to the adjacent materials.
  • Photographic media layers may become solubilized and be lost from the event or from the treatment procedure.
  • Fungal (mold/conidia) may grow in moist conditions, weakening the photographic binder and support, if organic in nature. Stains from these biologics may also occur throughout the structure of the photograph.
  • Physical distortion may occur during the process of attachment and be problematic to reduce after treatment.
  • Physical distortion may be necessary to aid in separation. This may cause permanent physical damage to the photographic image layer.
  • Physical damages such as skinning or tears of the support may also occur either from expansion and contraction cycles, or from physical attempts at separation.
  • Once separated, the sheen or color of the photograph may have changed. These changes are sometimes permanent in nature; sometimes reducible in appearance.

Techniques

Often determining the reason for and understanding the mechanism of attachment is key to choosing the best swelling, detachment, and removal method.
find pictures of paper on photo front; glass on photo; negative attached to negative "find pictures of the various set-ups described

Mechanical Approaches

  • Dry, resin coated photographs blocked in a stack can sometimes be separated with gentle force due to the coatings inherent with the photographs. If they don't release easily and cleanly, or if they retain moisture in the center of the stack, moisture methods can be tried.
  • Conversely, mechanical techniques may be required once the attachment is softened.
  • Insert a Teflon or plastic knife to help sheer away the connection near the attachment.
    • Slow, steady application can reduce the amount of potential stretching and stress to the gelatin image layer.
  • Scrape gently against the glass between the attachment with an unused razor blade.
    • Mat-cutter blades are best as they are smooth and have thin, acute angled bevels.
    • Blades used can be fashioned into a wooden stick (or end of a wooden or bamboo spoon) to extend the tool range if necessary. **Continuous motion create better results of separation.

Moisture Approaches

link to unmounting? or fill out here?
  • Gore-Tex (felted membrane)/Damp Blotter Pack (water as vapor)
    With Gore-Tex, and similar synthetics, such as Sympatex and Evelyn, water passes in small molecules when in direct contact with paper. Prior to the introduction of Gore-Tex membranes to the conservation profession, a damp blotter pack was used by conservators to introduce moisture. This method can be local or overall.
  • Ultrasonic humidifiers/Nebulizer (water as vapor/cold "steam")
    These machines produce moisture vapor. They can be locally used or used overall in conjunction with domed chambers and plastic tents.
  • Steamers (hot water gas)
    Useful when extremely fast and aggressive humidification is needed or for softening attachment and residual adhesives, however, more components of photographic prints can be adversely affected.
  • Misting/Water spray (water as liquid)
    Another traditional and faster method of dispensing water. Can deliver water too fast without sufficient absorption of the support.
  • Brush/sponge (water as liquid)
    Localized treatment to introduce moisture carefully, with much control.
  • Immersion (water as liquid)
    Partial or complete immersion. Temperature can be varied from cool to warm. PH levels and conductivity levels can be adjusted to fit the parameters of the material in question.
  • Poultices and Gels: (water as small molecule) capillary action requires even, continuous contact.

Alcohol and Solvent Approaches

  • If varnishes and similar coatings are the reason for the attachment, choosing an alcohol or organic solvent that softens the attachment is helpful to facilitate release. Alcohols and solvents can be introduced locally and overall.
    • Chambers
    • Gels
    • Emulsions,
    • Nebulizer use (vapor)
      • Because of the molecular size generated, this machine application should be used with caution and with full personal protection equipment
    • Direct application of liquid
      • Locally applied with small brush or sponge, purified water (distilled, deionized) or 1:1 ethanol water solution. Wait a few minutes for bond around edge to soften. Mechanical force, and use of a non-sticking knife or spatula may still be required to peel apart. Sometimes works best with fiber-based photographs than Resin coated photographs.
      • Overall immersion

Be careful using alcohols and solvents with colored photographic materials as some can alter the color dyes (e.g ethanol can fade chromogenic photographic materials over time, van Waldthausen from Lemmen and Lowe, 2017).

Differential Expansion or Contraction

  • Hot air guns and hairdryers
  • Dry ice (Dion, J 2002)

TIPS Specific to Attachment to Glass

  • Scan or digitally capture the image before treatment begins as a safeguard backup of image retention.

(tips from Clara von Waldthausen)

  • In some cases, breaking the glass close to an area of partial attachment can allow easier and safer access to areas that are adhered.
    • Insert soft, yet rigid supports gently between the photograph and glass before scoring and snapping.
    • Professional glass cutter can have better, more precision cutters (obtained from framing stores or suppliers)
    • For fiber-based DOP's, strike with the ball end of a glass cutter, near an edge of the bond. The vibrations sometimes dislodge the gelatin (from Sylvia Verselli, 2003 workshop).

TIPS Specific to Attachment in a Stack of Like Photographs

  • 2 - 3% Gellan gum gel or 3-5% Agarose gel can soften stacks of blocked prints and sometimes negatives, very effectively through humidification. If the photographs are not moldy, agarose gels can be cleaned, rinsed, and rejuvenated in same conductivity and pH baths/trays of the original gels for several hours or over night and thus re-used each day until the project is complete. It is assumed whatever pollen, salts, or debris found is likely the same throughout blocked materials. Re-using the same gels for different projects is not recommended as unknown or undesirable contaminants may be transferred. Judgement and experience of the conservator is required.
  • For small personal commercially processed gelatin DOP prints, both colored and black-and-white, Gore-tex, blotter stacks, and gel sheets can be applied and kept moist while in a zip-lock style baggie or very small covered, photographic trays.
    • For separating large batches of photographic prints, it is helpful to pre-cut Gore-tex felts or gel sheets, poly(ester) webbing, very lightweight Japanese papers, and blotters slightly larger than standardized photographic processes, yet smaller than the container chosen.
    • Additional small poly(ester) webbing sheets can be inserted into areas not currently attached, or previously released to reduce the chance of reattachment.
    • Both Gore-tex felt or gels require continuous contact to work best. Minimizing air in the container allows dampened felts and gels to retain moisture longer.
    • Check periodically, but this process often takes a few hours.
    • Once humidification begins, it is common for several photographs to detach in succession. Steady, quick work is required while the attachment bond is soft enough to release.

TIPS Specific to Emergency Triage Situations

For more information, please see ["link to PMG EMERGENCY PAGE" and "AIC's SALVAGE PAGE]

Photographs Adhered to The Glazing

  • Materials should be kept damp by wrapping in plastic provided a conservator will be able to treat them within 48 hours.
  • Prioritize anything stuck to glass for immediate treatment. If the glazing is acrylic, the photograph should release on its own once it is dry, of course the surface will likely still be altered where it was stuck.
  • Immerse in water: ideally the photograph should lift off without a great deal of force. Do not pull a photograph off at an acute angle that can cause cracking in the emulsion.
  • If immersion is not a possibility, place release materials under the areas that are not stuck and place thin spacer material such as blotter between the glazing and the release material to try to encourage gradual release and prevent more areas from adhering.

Photographs Stuck to Themselves

  • If wet and stuck in a stack, gently peel apart resin-coated or commercial color snap shot photographs at a low angle only if possible. Do not force separation. Some image loss may occur.

Photographs Stuck to Plastic Enclosures

  • Materials should be kept damp by wrapping in plastic provided a conservator will be able to treat them within 48 hours.
  • Cut three sides of the enclosure and peel the plastic carefully off the emulsion surface using an acute angle while keeping the photograph flat. Avoid pulling wet photographs from their protective enclosures. Release slides also, as plastic and paper mounts may also be stuck to the enclosure. Be especially careful of acetate materials as they may be extremely sticky.

Specific Note-Worthy Situations

  • Photographic album black mounting paper can leave dye stains and fibers imbedded within a gelatin matrix after separation and release.
  • The coating on "erasble" typing papers can form a particularly tenacious bond with gelatin layers, whereas an uncoated bond typing paper may more easily release.

Beyond Separation, Post-release Guidelines and Recommendation

  • Once-separated, the material may remain swollen or distorted. Drying may be immediately necessary requiring pressing either locally or overall. See [Drying, and Flattening].
  • Once separated, materials can be isolated to reduce the likelihood that re-attachment may occur. Isolation can be placing a photographic or negative in Mylar sleeves, Mylar or paper folders, or creating mats or inserting glass separators when framing. However, if a water event is sustained long enough, paper-based photographic materials can swell and distort beyond the air-gap space and distance provided by a traditional 4-ply mat.

References

(see AIC Website for Style Guide - generally uses Chicago Manual of Style)

  • Dion, Judy. 2002. "Notes on Treatment Procedure: Removal of Glass from a Painted Surface". Unpublished student research paper for Winterthur/University of Delaware Art Conservation Program. (additional 2020 personal communication with SWs. <<< take out after completing section)
  • Edwards, Gwenanne. 2011. Works of Art on Paper Adhered to Glass: Approaches to Conservation Treatment. Unpublished student research paper, Buffalo State Art Conservation Program. (additional 2020 personal communication with SW. << take out after completing section)
  • Lemmen, Barbara and Emma Lowe. 2016. Blocked Photographic Prints: Adhesion and Treatment. Presented at the PMG session of the 2016 AIC Annual Meeting in Montreal, Canada. AIC: Washington, D.C.: Topics in Photographic Preservation, Volume 17 (2017) 29-50.
  • Norris, Debra Hess. 1989. The Removal of a Silver Gelatin Photograph Adhered to Glass. AIC: Washington, D.C.: Topics in Photographic Preservation, Volume 3 (1989), 86-91.
  • Warda, Jeffrey, Irene Brückle, Anikó Bezúr, and Dan Kushel. 2007. "Analysis of Agarose, Carbopol, and Laponite Gel Poultices in Paper Conservation." Journal of the American Institute for Conservation 46(3): 263-279.


  • Other separation articles and techniques (look at varnishes/varnished map sources as well)
  • Gels info



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