PMG Consolidation and Flattening of Cracks
|Date initiated||June 2014|
|Contributors||Gary Albright, Luisa Casella, Thomas M. Edmondson, Stephanie Watkins|
Purpose of Consolidating and Flattening 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.
Factors to Consider Before Treatment
- Careful observation of the structural condition of the various layers comprising photographic materials may help determine suitability of any approach. For instance, a gelatin image layer that has suffered water damage may have lost the ability to withstand any humidifying and flattening procedure.
- The photographic emulsion surface can be changed from the application of heat, moisture, and pressure.
- Use of heat, moisture, and pressure can be applied overall or locally. Consider the after effect of each approach.
- Choosing consolidation methods using heat and pressure are generally safer methods than those also incorporating moisture.
- If moisture is necessary, restrict application to the back (non-image side).
- Steady hands, skill, and tidiness in adhesive (e.g. gelatin) application is important. The appearance of the image, and specifically any silver mirroring present, can be altered with any stray adhesive application remaining on the surface prior to heating.
Effects of Consolidating and Flattening Cracks in Silver Gelatin DOP
- The effects of consolidating and flattening cracks in the image layer are structural through the consolidating steps, and visual as a result of the flattening process.
- Depending on the procedures used, consolidating and flattening can occur overall or locally to the photographic print.
Equipment and Materials
Not all equipment and materials listed will be needed for each application approach.
- Small hot plates (with adjustable temperature), mug/coffee warmers, candle warmers (to keep gelatin warm)
- Fine tip round brush, either natural or synthetic fibers
- Magnifiers, readers, optivisors or microscope
- Teflon or bone spatula
- Tacking irons with adjustable temperature (such as Seal/Bienfang Selector, Drytac, Gundlich, brand models)
- Heated metal-tipped tools with adjustable temperature (such as Coverite brand sealing irons, Clover brand mini irons, hot tacking tools, tip-modified soldering irons). Handmade or modified tips of different shapes, sizes, thicknesses, and lengths made from heat conducting metals (such as copper) can be attached to some heat tools.
- Heat press, dry mount press
- Steel plate (such as a metal dry mount cooling platen), glass, drying press, blotter stack with thick acrylic or glass platen and weights
- Photographic grade gelatin, 250 Bloom-surface
- Humidification chamber (tray, plastic grating, acrylic cover, humidity indicator strip)
- Silicone release paper
- Permalife bristol folder
- Smooth unwoven polyester webbing such as Hollytex; continuous pore better
- Photographic grade blotters
- Mending papers: Japanese kozo papers, light weight
- Mending adhesives: Wheat starch pastes, cellulose ethers (such as methyl cellulose, hydroxypropyl cellulose, etc.)
The treatments used to consolidate and reduce cracking are often variations of procedures developed by the late Jose Orraca, described in print by Ana Hofmann in 1991. Their procedure is outlined last as less invasive variations have developed in the intervening years.
Albright (2017) Reducing Cracks in Gelatin Photographs
The listing follows Albright's general treatment order of least to more invasive methods. From experience he as learned that if heat causes problems, it is usually when used in combination with overall humidification.
- Apply localized and overall heat applications, such as with a tacking iron or dry mount press.
- Apply localized moisture on the reverse, then dry with a tacking iron from the back.
- Apply gelatin to the back of the crease, then dry with a tacking iron on the back.
- Apply gelatin to the front and back of the crease, then dry with a tacking iron on the back.
- Apply localized moisture and gelatin, or gelatin alone, then dry in a heat press.
- Sometimes, careful burnishing of the print through polyester webbing (Reemay, Hollytex) or silicone release paper (Seal/Biengfang) before drying with the tacking iron or in the heat press may need to occur.
- Apply localized moisture and gelatin, or gelatin alone, then left to air dry. Followed by light misting or spraying of moisture on the reverse of the print and dried in a heat press.
Orraca - Hofmann (1991) Flattening Cracks in Photographs
This approach relies on the application of gelatin, moisture, and heat and works best when applied to the treatment of single weight glossy gelatin photographic prints.
a) Crack consolidation with warm diluted gelatin while working under magnification.
Starting with a warmed (1:8) gelatin:purified water mix, dilution can be adjusted during treatment at the discretion of the conservator based on the photographic print being treated. Apply one coat of warm dilute gelatin to inside of the crack using a very fine brush. If gelatin over spill occurs, clean using a damp cotton tip immediately. Any excess gelatin left on the surface will appear as a noticeable surface sheen difference (often as a shiny area) after the application of heat during the flattening step. Turn the photograph print over and apply two coats of warm dilute gelatin to the area of the crack from the back, allowing the gelatin to dry between applications. This will pull the paper towards the back, returning the photographic print to its original plane. When the gelatin is dry, place the print between silicone release paper inside a Bristol weight folder in a dry mount press at 185°F 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, particles, dings or creases that may disrupt the image layer during flattening.
b) Overall humidification
Humidification will relax the image layer and support overall, and reduce the appearance of the crack areas. Hofmann describes as her preferred process of placing the photographic print between layers of unwoven polyester webbing and damp blotters while under glass for approximately 5 to 20 minutes. Alternatively, place the photographic print in a humidity chamber for approximately 30 to 45 minutes. Humidification duration will depend on the humidification method chosen, time the set-up has been in place, and actual ambient humidity levels in any work environment. Refer to humidifying section for more information.
c) Overall flattening and drying in a heat press
Place the photographic print between new, clean, flat silicone release paper, inside a Bristol-weight folder in dry mount press at 185°F for 45 seconds.
d) Overall flattening under weights
For optimal results, immediately place the warmed photographic print in a short blotter stack (between two layers of smooth polyester webbing, blotters and rigid platens while under weights) for a minimum of 48 hours, longer if possible.
e) Additional support
The crack area may require additional mending and reinforcing on the back. A variety of conservation quality papers and adhesives can be used at the discretion of the conservator.
Tips and Recommendations
- Dust-free, if not pristine, new support materials (polyester webbing, release papers, folders, boards, etc.) are essential to use.
- Restricting gelatin application to the crack area on the front and back, then drying under localized weights prior to reinforcing the support with Japanese paper can be sufficient action to consolidate some cracks.
- Overall flattening can occur by placing the photograph in the dry mount press at low heat, then turning the press off. Let the print cool down in the press. Refer to flattening section for more information.
- Alternatively, overall flattening while cooling can occur under a heavy, cool platen such as metal or glass. Be careful of using platen materials that may retain heat longer than an historic photograph can withstand. Often transferring the photographic print between new smooth polyester webbing, release papers, folders, or boards is desirable.
- Albright, Gary. 2017. Reducing Cracks in Gelatin Photographs from Using the Dry Mount Press in Conservation, Handout from presentation at the AIC-PMG Winter meeting, Kansas City, MO
- Hofmann, Ana B. 1991. Flattening Cracks in Photographs. Topics in Photographic Preservation 4:166-169
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