PMG Consolidation and Flattening of Cracks

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Photographic Materials Conservation Catalog
Consolidation and Flattening of Cracks

Date: Initiated June 2014
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 Consolidation and Flattening of Cracks

Photographic materials often exhibit cracks in the image layer. These may be a result of misshandling, variations in humidity, temperature or exposure to water followed by fast drying. The purpose of the treatment is to consolidate image layer material and flatten area to restore its original surface continuity.

Consolidation and Flattening of Cracks in Silver Gelatin DOP

Consolidation and flattening of cracks in silver gelatin DOP

Factors to Consider Before Treatment

Observing the structural condition of the various layers will determine if the process will be successful. For instance, a gelatin image layer that has suffered water damage may have lost the ability to withstand a successful humidification and flattening procedure.

Effects of Consolidation and Flattening of Cracks in Silver Gelatin DOP

The effects of consolidation and flattening of cracks in the image layer are structural through the consolidation steps, and visual as a result of the flattening process.
In addition, as a result of the humidification and flattening step, the entire support of the object will be flattened.

Equipment and Materials

  • Equipment
    • candle warmer
    • fine tip brush
    • optivisors or microscope
    • teflon or bone spatula
    • heat press
    • drying press or thick acrylic and weights
  • Materials
    • Japanese paper
    • Wheat starch paste
    • Photograde gelatine - dissolved 1:8 in water as stock solution (initially soaked in cold water for 1 hour, then warmed to dissolve), then diluted in equal amount of water (dilution can be adjusted during treatment)
    • Humidification chamber (tray, plastic grating, acrylic cover, humidity indicator strip)
    • Silicone release paper
    • Permalife bristol folder
    • smooth unwoven polyester web such as Hollytex
    • blotters


The following technique was developed by Jose Orraca and described by Ana Hofmann (Hofmann 1991) and relies on the application of gelatin, moisture and heat. It is particularly successful in the treatment of single weight glossy prints.

  • a) Mend and reinforce support - from verso, apply Japanese paper strip to area of crack (often accompanied by support crease), and/ or mend support tears (make sure to properly align image layer). Let dry under holytex/ dry blotter/ glass/ weight.
  • b) Crack consolidation with warm diluted gelatine - working under magnification, apply one coat of warm dilute gelatin to inside of crack using very fine brush. If overspill occurs, clean using damp cotton tip - any excess gelatin will appear as a shiny area after the application of heat during flattening step. Turn object over and apply two coats of warm dilute gelatin to area of the crack from the back, allowing to dry between applications. This will pull the gelatin towards the back, returning it to its original plane. When the gelatin is dry, place print between silicone release paper inside a bristol folder in dry mount press at 185F for 45 seconds to set the gelatin. It is most important that the silicone release paper be completely flat (it will cockle with moisture) and clean of any dust or particles that may disrupt the image layer during flattening.
  • c) Overall humidification in chamber - this step will relax the image layer and support overall, and reduce the appearance of the crack areas. Hofmann describes as best process to place object between layers of unwoven polyester web and between damp blotters under glass for 5 to 20 minutes. Alternatively, place in humidity chamber for 30 to 45 minutes.
  • d) Flattening and drying in heat press - Place print between new, clean, flat silicone release paper, inside bristol folder in dry mount press at 185F for 45 seconds.
  • e) Flattening under weights - place under weights between two layers of Hollytex and blotters for a minimum of 48 hours, longer for optimal results

Guidelines and Recommendations

  • Good results may be achieved also by starting the treatment with the application of gelatine to the crack area (front and back), prior to reinforcing of the support with Japanese paper
  • Placing the photograph in the dry mount press and turning it off, letting the print in the press to cool down may also yield good results in the flattening step


  • Hofmann, Ana B. Flattening Cracks in Photographs, 1991. Topics in Photographic Preservation 4:166-169

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