PMG Unmounting

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Photographic Materials Conservation Catalog
Unmounting

Date: Initiated July 2014
Contributors: Amanda Maloney, Luisa Casella, Thomas M. Edmondson, Saori Kawasumi Lewis, Stephanie Watkins

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. Best professional judgement is necessary when using or interpreting information provided.

Purpose of Unmounting Photographic Materials

Stereo albumen prints partial detachment from original mount is causing physical stress to print support

The purpose of unmounting photographic materials is to separate photographs from secondary mounts. Secondary mounts may contribute to deterioration of an object (e.g. be brittle, acidic or otherwise unsuited) and therefore best separated from the photograph, or it may be preferable to unmount in order to best perform a treatment.

Factors to Consider Before Unmounting

  • Type of photographic process.
  • Type of mount and adhesive used.
  • Condition of all of the elements.
  • Benefits and disadvantages of unmounting.
  • Plan for any future remounting understanding original expansion and contraction rates of the material.
  • Artistic intent: Photographer's original aesthetic.
  • Whether the photograph was previously backed or mounted originally.
  • Historical provenance of mount including photographer's signature and manufacturer's or photographer's stamps and writings on the mount.

Effects of Unmounting

  • Unmounting separates the object from (a) secondary support(s).
  • Aesthetic of the historic photograph, valuable signature, or historic provenance can be lost through unmounting. Sometimes the cover paper of a signed matboard can be saved for remounting onto another core.
  • Mounts can be a physical protection for thin photographic supports that is lost when the photograph is unmounted.
  • The process of unmounting can create plastic deformations within the photograph that are difficult to remove or make remounting challenging.

Unmounting Techniques

Separating an object from a secondary mount requires great caution in order not to damage the photograph during the process. Techniques may be used in conjunction with each other or in a sequence. For additional insight into removing paper and paperboard backings from photographs, see Backing Removal. It is important to understand the various unmounting techniques before deciding on the most appropriate approach given the condition and type of photograph.

Dry Mechanical

Face-up Separation

Face-up separation methods require mechanical force using a blade, spatula, or knife inserted within the mount for the purpose of releasing the photograph. Knife insertion may occur at various positions, from below the photograph within an adhesive layer, or under a cover paper, dry mount tissue, or between mount board plies. A very thin, flat blade is often preferred.

  • Advantages:
    • Faster than face-down separation methods.
    • Best suited for boards with barrier papers, dry mounted photographs, and thick or desiccated adhesive layers mounting the photograph to the board.
    • Best suited for more robust photographic papers without existing tears or punctures that can withstand the differential strain this method can create.
  • Disadvantages:
    • Greater risk for distortions, rips, and punctures to occur to the original photograph than with face-down separation methods.
    • Best suited for completion in one-continuous motion. Stopping part-way can produce plastic distortions within the photograph.
  • Tools:
    • Thin Teflon blade or spatula, metal spatula, microspatula, minarette (sculptor's tool), painting knife (palette knife), honed Casselli spatula, hot plate or hors d'oeuvre warmer.
    • Teflon coated or Goretex ribbon dental tape.
  • Factors to consider:
    • Face-up separation of a photograph from its mount is not a one-step procedure, rather, it is usually the first step of several in a treatment process.
    • Face-up separation can remove a photograph from its mount, or it can be a board-splitting procedure where the facing paper remains attached to the photograph. If important information on the mount requires saving, it can be removed in a face-up dry removal by tool insertion directly under the facing paper and shearing away. Any residual material on the back of the paper can be removed with either moisture poultices or immersion methods.
    • Face-up separation works best with double-weight photographic papers, rather than thinner papers, such as albumen papers, and the photograph must be in good physical condition to tolerate the stresses that will be imposed on it.
    • Face-up separation works best when the mounting adhesive is weakened from degradation or the mount board is degraded and brittle.
    • The edges of a degraded mount board will be easier to penetrate than areas under the photograph that have been protected from light or other oxidizing contaminants. The same is true for the photographs.
  • Procedure:
    • Insert your tool of choice (palette knife, honed Casselli spatula, Teflon knife etc., see tool list) into the mount board at the closest point to the facing paper or photograph as safely possible and shear away, being careful to stay on one plane within the same layer. Listening to the sound of the shearing action (it should be consistent) and use of a raking light can help keep the tool at the same layer during the process.
    • Once separated from the mount, remove residual mount fibers and adhesives from the back of the photograph (See Face down, humidity section).
    • Dry mounted photographs can be removed face-up by shearing under the dry mount tissue and removing the tissue in separate face-down steps (see Face-down and dry mount sections).

Face-down Separation

Face-down separation methods require mechanical force using a blade or knife to carve away the mount. Potential damage during treatment can be reduced by keeping a clean work area: Place the photograph on a clean, smooth surface. A blade or knife with a slight upward curve can help direct any tool slippage away from the photograph. Or, if there are distinct plies, work with a honed Casselli spatula. Honing should be done on one side of the blade only, leaving a flat bottom for better control while shearing and paring. Some mount boards that appear not to have layers turn out to have them, but not distinct plies.

  • Advantages:
    • Slower, more controlled procedure than face-up separation.
    • Paring down slowly along natural board and adhesion levels can help reduce distortions within the photograph during unmounting.
  • Disadvantages:
    • Scratching or other physical damage from dust and debris is more likely to occur to the surface of the photograph.
    • Dents and deformations can occur to the photograph from the back.
    • Punctures and tears are more likely to occur as paring moves closer to the back of the photographs.
  • Tools:
    • Metal tools: Thin Teflon-coated spatula, microspatula, minarette (slightly curved sculptor's tool), painting or palette knife, scalpels (curved blades preferred over straight, pointier styles), honed Casselli spatula
    • Thin Teflon blade
    • Heavy weight pressure-sensitive tape
    • Localized weights and platens
  • Factors to consider:
    • The mounting board is destroyed during this procedure.
    • Mount boards with grey core can be extremely difficult to work with, and dry options may be very limited.
    • For the conservator, unmounting face-down can put much prolonged strain on the wrist and hands, neck and shoulders. A wrist support can help reduce pain or damage from repetition. Periodic stretching, frequent breaks, and short work periods help reduce physical tension.
  • Procedures:
    • After the back facing paper is salvaged for remounting or saving any important information, face-down unmounting is frequently completed by paring away the core material. If the mount is a laminate structure, it can be taken away layer by layer using a tool of choice.
    • It is best to weight the photograph with enough weight to keep it from slipping, and it is usually easier to work towards the weighted area. Once the weighted area is reached, switch the weight to the pared area and finish paring the mount in the area previously under the weight.
    • Look for frayed edges for easy access when beginning. Try all four edges to find one that will provide the easiest and smoothest access. Begin work from that edge that is the softest and easiest to penetrate or separate plies. Boards usually have a direction that allows easier delamination.
    • Paring down a mount horizontally, slowly layer-by-layer introduces less mechanical stress to the photograph than paring down in a vertical fashion from the back to the layer of the photograph.
    • Stubbing or poking the mount with a honed spatula provides the greatest opportunity to cause damage rather than clean removal of mount material.
    • If there is a tear or a break in the object, work parallel to it as to not extend the tear or break.
    • Clean up debris frequently, preferably with a low vacuum, to avoid creating too much dust by brushing.
    • As you approach the back of the photograph, determine if a front facing paper exists (there almost always is one).
    • At the level of the back of the photograph or front facing paper, it can be a safer procedure to use moisture poultices to remove the remaining mount material.
    • If washing the photograph is part of the treatment protocol, immersion of the photograph at the point when only a thin layer of facing paper is attached, can remove any remaining paperboard material and adhesive.
    • If washing the photograph is not part of the treatment protocol, using damp cotton swabs with purified (e.g. distilled or deionized) water can clear the back of the photograph of any remaining paper, board or adhesive.
  • Removing dry mounts adhesive/paper layers
    • Early shellac-based dry mount tissues that are now aged can lose their adhesive properties, allowing them to peel off dry without heating. Complete removal of residual adhesive usually requires use of solvents, although sometimes it can be removed face-down, dry by scraping or sanding.

Board Splitting

Splitting is a forceful mechanical action aiming to reduce the bulk of thick boards and to minimize the exposure of photograph to moisture. This procedure can be used to repair a damaged mount when a complete removal is not desirable. Splitting only applies to boards with a laminate structured core. This procedure is done almost entirely from the back. If, for some reason, a decision has been made to work face-up, multiple splits of thin sections are less stressful for photographs than trying to remove large, thick sections of boards at a time. Board splitting techniques should not be confused with paper splitting techniques.

  • Advantages:
    • Reduces time required to unmount items through face-down methods.
    • Can make face-up methods easier by making the mount less rigid.
    • Easiest to perform on dry, brittle boards.
    • Helps to minimize exposure to moisture.
  • Disadvantages:
    • Mount is destroyed during the process.
    • Procedure can cause torquing and tension stresses within the photograph.
    • If done improperly or face-up, the photograph may crease or tear.
    • It can be very difficult to split newer boards evenly, and without considerable force.
  • Tools:
    • Metal tools: Thin Teflon-coated spatula, microspatula, minarette (sculptor's tool), painting knife (palette knife), honed Casselli spatula
    • Teflon knife
    • Teflon coated or Goretex ribbon dental tape
  • Procedure:
    • Refer to Face-down separation for detailed procedures.
    • Whenever possible, work face-down for the least risk to the photograph.
    • Look for frayed corners or edges for easy access to the core.
    • Find the direction of least resistance by testing from each edge.
    • If back facing paper is to be salvaged, insert your tool of choice as close to the back facing paper as possible and sheer away.

Humidity

Gels and Poultices

Working with the photograph face-down, moisture or a moisture poultices, such as dilute methylcellulose paste, can often soften water-based attachments sufficiently to allow mechanical removal with a scalpel, polyester or Teflon knife, scraper, or other appropriate tool.

Water Vapor/ Humidity Chamber

Placing the object in a cool or room-temperature humidity chamber is generally not enough to soften and reactivate the adhesive and separate the object from mount. Humidification is generally reserved for flattening.

Gore-Tex Sandwich and Damp Blotter Pack

Gore-tex sandwiches and damp blotter packs are alternative methods to humidity chambers and will humidify at a a much faster rate than a humidity chamber, but may not adequately humidify heavier mount boards. Gore-tex or polyester webbing in direct contact with the photograph and mount is required for optimum results. The speed of the process can be easily regulated by the amount of moisture within the blotters and the amount of pressure applied to the stack. The ambient humidity and temperature of the work environment will also affect the amount of moisture needed to relax the photographic materials. Poly(ester terephalate) film (Mylar, Melinex) or Gore-tex tape can be used as a mask to isolate areas that the conservator wish stay dry (or less humidified) during the process.

  • Advantages:
    • Slow humidification poses less risk to the photographic image.
    • Humidification with a small water molecule (vapor) allows deeper and faster penetration of moisture than humidification within a chamber without having the photograph in direct contact with water.
    • Reduces risk of denting support by applying pressure (as in dry-mechanical).
    • Secondary support remains intact.
    • For large, or panoramic supports, the adhesive can be softened and the photograph released incrementally.
    • Ideal for larger items that may not safely fit into a humidity chamber, yet does not exceed the shortest dimension of the Gore-tex.
    • Precision humidification possible with masks.
  • Disadvantages:
    • Humidification may adversely soften photographic processes.
    • The condition of the item may make humidity procedures risky.
    • Photographs may tear or crease more easily once humidified.
    • Introducing moisture may cause blurring, bleeding, and migration of writing, stamps, and marks, and also affect applied color or coatings.
    • Humidification may be ineffectual to soften the adhesive attachment.
    • Physical pressure required to create the Gore-Tex sandwich or damp-blotter pack may adversely affect photographic surfaces.
    • Pressure, in combination with moisture, may cause photographs to become attached to the stack materials during the humidification process.
    • Depending on how the sandwich or stack is set-up, the photograph may not be visible during humidification.
    • Masking materials may have sharp edges that can score, abrade, cut, or crease photographic materials.
    • Gore-tex brand felted, laminated membrane may be discontinued (early 2010's). Gore-tex film (smooth side) still available. EPIC® fabric can also be used in place of Gore-tex.
  • Tools:
    • Clean water source (deionized, distilled)
    • Gore-Tex, commercial laminate product of felted and smooth poly(tetrafluoroethylene), (ePTFE); SympaTex (polyester-based) laminate membrane may be a suitable substitute
    • Photographic grade blotters
    • Poly(ester terephthalate) film (Mylar Type-D, Melinex 516, thin mil preferred)
    • Glass or Acrylic glazing
    • Weights

Steam

Steam is usually used in conjunction with immersion techniques, but is sometimes used in conjunction with dry-mechanical removal in early unmounting stages to speed up the process, or in final process to soften, then reduce, adhesives.

  • Advantages:
    • Steam will impart more humidity than the previous methods as well as heat likely increasing speed of softening of mounting adhesive.
    • Can be applied in large areas or more precisely with pencil-type tools for more control.
    • When used with brush applied water, or a gel or cellulose-ether "poultice", moisture can penetrate quickly and with precision.
    • Effective in reducing residual adhesives.
  • Disadvantages:
    • Steam, being a combination of moisture and heat, can deteriorate and damage photographic materials.
    • Steam may adversely soften photographic image layers.
    • The condition of the item may make humidity procedures risky.
    • Photographs may tear or crease more easily once humidified with steam.
    • Steam may more quickly cause blurring, bleeding, and migration of writing, stamps, and marks, and also affect applied color or coatings than other cool or room temperature moisture applications.
    • Steam may release large quantities of discoloration from the mount that can deposit in the photograph.
    • Steam may drive adhesives into the photographic structure.
    • Steam may quickly cause wrinkling and expansion of the support.
    • Using steam may be ineffectual to soften the adhesive attachment.
  • Tools:
    • Horizontal steamer, garment steamer
    • Cellulose ethers (e.g. Methyl cellulose)
    • Metal and Teflon spatulas
    • Brushes, sponges, cotton (roll, ball, swab)
    • Clean water source (deionized, distilled)
  • Procedure:
    • It is assumed that testing has been done to verify that the photograph and any inscriptions and labels can tolerate wetting.
    • Pre-humidification by humidity chamber or misting is always an option prior to immersion.
    • Fully saturate the photograph and the mount by immersion in water.
    • Be aware that the application of steam is usually most safely done with albumen and salt prints.
    • Be aware that the use of steam does not have to mean direct blasting of the photograph. Try to work with the steamer held at the farthest distance from the photograph at which it is effective.
    • When steam is being most effective, separation of the photograph from the mount or facing paper should be effortless.
    • Gelatin prints can sometimes be safely treated with steam from back, but this requires frequent checking of the emulsion from the front to be sure that it is remaining stable.
    • Direct application of steam on gelatin emulsion can be destructive and rapidly so.
    • Be aware that collodion prints with a baryta layer usually cannot tolerate prolonged wetting by immersion or misting. Collodion prints without a baryta layer are usually more robust and can tolerate wetting, but steam has to be used with caution.
    • When extensive application of steam is necessary to accomplish separation, it is best to work with the photograph face down on a clean wool felt. Be aware that steam will adversely affect any polyester web or polyester sheet. The felt allows the steam to go through without pooling under the photograph.
    • The application of steam is usually most effective when removing a mount of a laminate structure or when saving the mount core is not necessary.
    • The use of steam can cause blistering of albumen emulsion from its paper support, this is usually related to prior severe water damage of the print.

Immersion

Immersing the mounted photograph on a screen or other carrier in water may be used where the condition of the emulsion and any inscriptions or labels have tested extremely stable. Frequent water changes are often necessary. Photographic mounts will have a slower uptake when immersed in cool, or room temperature water than heated water. This process is usually used when the decision has been made to keep all, or the facing papers, of the original mount for reuse.

  • Advantages:
    • This method can be very fast in softening the adhesive and separating the photograph from the secondary support.
    • Adhesive reduction is likely to be more even.
    • All components of the assembly will likely remain intact after drying.
  • Disadvantages:
    • Direct contact with water may adversely affect binder, image layer, applied color and coatings that may soften, migrate or dissolve.
    • Boards can take up water so slowly that dramatic bowing and other distortions initially occur.
    • Photographs can tear under the strain when a board takes up water too quickly and expands dramatically.
    • Discoloration and dyes from the mounts may migrate to the photograph.
    • Photographic materials are easily torn or creased when handled when wet.
  • Tools:
    • Tray
    • Appropriate hand tools (spatula, palette knife, etc.)
    • Glass weights of your choice
    • Clean water source (deionized, distilled, filtered)
    • Window screens (smaller than tray, larger than photograph)
    • Poly(ester) webbing and/or sheeting
  • Procedures:
    • Complete all appropriate spot testing for solubility parameters of emulsions, inks, etc.
    • Pre-humidification may help minimize planer distortions with initial immersion.
    • Select a tray with adequate room for manipulations with tools and handling of the photograph.
    • Fill the tray with an adequate amount of water to ensure full immersion.
    • Immerse the photograph and the mount, weight as necessary to keep submerged. Be aware that frequent changes of water may be necessary to avoid migration of discoloration into the photograph.
    • Wait as necessary and test for release progress. Be aware that this can either go quickly or slowly.
    • Increasing the temperature of the water may be necessary to get release.
    • If necessary, refer to "Steam" above.
    • Upon release, be sure to have an appropriate support/carrier for the photograph, and/or facing papers.
    • Have a drying station prepared with felts, blotter, polyester webbing, etc.

Solvents

Solvents may be introduced in a bath, from a chamber, directly with a cotton swab from the verso of the secondary mount or wicked in slowly via a metal spatula.

  • Advantages:
    • Immersion in the correct solvent can release photographs quickly by effectively softening and reducing the adhesive bond without much physical stress. However, sometimes physical manipulation is necessary.
    • Short immersion times are possible if objects do not have thick boards or double-weight papers.
    • It is possible (but not probable) that exposure to solvent fume/vapor over a very long time can effectively soften the adhesive bond requiring only the minimal physical manipulation for removal of mount from photograph.
    • Mounts can remain intact.
  • Disadvantages:
    • Solvents can dissolve or dislodge photographic media, as well as signatures, stamps, and other historic markings unseen on the back of the mounted photograph.
    • Color photograph dyes can be very soluble in organic solvents.
    • Solvents can release dyes from the mounts that potentially can deposit in the photograph. In particular, the ketones (acetone and methyl ethyl ketone) can release blue-dyes, possibly whiteners and optical brighteners, from boards.
    • Long immersion times may be necessary if the photograph is printed on a thick support, such as double-weight paper.
    • Likewise, longer immersion times are generated when photographic mounts are not reduced or removed prior to immersion. Solvents are slow to penetrate adhesives used to create thick, dense, multi-ply boards and thick mounts absorb much solvent, in general.
    • Leaving a photograph with a baryta layer in solvent baths for extended periods of time may leave the baryta layer with permanent solvent tide-lines.
    • RC papers, whether black and white or color, that are considered able to tolerate immersion will take in solvent at the edges and it will take a very long time to migrate out. This can result in the photograph becoming hazardous material.
    • Solvent baths can redeposit modern adhesive materials over the photographic image with insufficient bath changes. Adhesives that dissolve can redeposit when the solvent solution becomes "saturated". Some acrylic-based adhesives do not dissolve, but gel and "glob" in solvents, making it possible for them to redeposit on the surface once dislodged into the more liquid solvent.
    • Adhesives that actually fully dissolve can be driven into paper-based photographic materials when in long-term solvent chambers.
    • Solvents can have long-term, as yet unknown, detrimental consequences to photographic materials.
    • Solvent use requires proper ventilation in the work area and personal protection equipment for the conservator.
    • Using large quantities of solvents can be an expensive option compared to other methods. Besides purchase and hazardous material transportation charges, disposal of used solvents as hazardous waste can be costly. Please correctly dispose per your local jurisdiction.
  • Tools:
    • Natural bristle brushes
    • Cotton swabs, balls, or roll
    • Paper towels
    • Metal tweezers, palette knives, spatulas, etc.
    • Clean high-quality blotters
    • Small glass chambers
    • Large stainless steel (solvent grade) or inert plastic trays
    • Large chambers made of inert poly(ester terephthalate) film
    • Organic solvents to release adhesive (testing required to determine most effective ones appropriate for each photograph)
    • Personal protection equipment (e.g. respirator plus chemical-specific filters, chemical specific resistant gloves, and smock)
    • Fume extraction equipment
  • Local Procedures:
    • With smaller photographs, working face-up and using a large, flat clarinet reed, spatula or a palette knife dipped in solvent can be an effective way to deliver solvent between the photograph and the secondary support without having to resort to immersion.
    • This procedure has less risk of staining the photograph when dealing with more modern adhesives.
    • This procedure has greater risk of puncturing or tearing the photograph than immersion methods.
    • Clearing the verso of residual adhesive will be necessary after separation.
  • Immersion and Chamber Procedures:
    • Spot testing is not the same thing as immersion.
    • Most of the time, it is in your best interest to get rid of as much secondary support materials as possible prior to immersion. The extra paper boards will absorb more solvents (costly and unwieldy).
    • Trays, screens, polyester-webbing, and tools should be tested for "solvent sturdiness" prior to use lest they "melt" during the procedure.
    • Once it has been determined that immersion is appropriate for the photograph, it is important to let the solvent do the work. Patience is key to allow enough time for total penetration and dissolution or softening of the adhesive.
    • For modern adhesives it is important to monitor the bath for floating globs of gelled adhesive. Change baths as necessary to minimize the potential of deposition of adhesive on the surface of the photograph.
    • For synthetic adhesives that primarily swell in solvents whether in immersion or chamber, final removal will require mechanical swabbing with cotton balls or scraping with spatula from the back, while the photograph is face-down.
    • For older 20th century adhesives that tend to be soluble in polar solvents, it is important to monitor the bath for clarity and change as necessary to avoid staining of the photograph.
    • Newer dry mount materials generally require high heat to release, followed by removing residual adhesives with solvents. Heating in large sections or overall, can increase speed while reducing potential distortions during the process. Both immersion and chamber solvent exposure can be effective in softening up and releasing residual synthetic adhesives.

Temperature

Some thermoplastic (melting polymer) adhesives may soften by applying local or overall heat. Further mechanical action or solvent use may be needed to reduce any adhesive residues. Thermosetting (cured polymer) adhesives may become even more difficult to remove after reintroducing heat. Freezing efforts are generally ineffective toward changing the glass-transition temperature of either adhesive for release.

  • Advantages:
    • Easy procedure.
    • Less toxic than solvent use.
  • Disadvantages:
    • Heat can permanently damage resin coated photographic papers, creating melting, discoloration, cracking, and other plastic distortions.
    • Heat can inversely increase the adhesive bond making removal even harder.
    • Heat can drive some adhesive films farther into paper-based photographic materials.
    • A large block of time may be necessary. Stopping partially may introduce plastic deformation into the photograph.
    • Cold mount adhesives do not respond to heat.
  • Tools:
    • Hot air pencils, hair dryers
    • Hot platens: cup warmers, slide warmers, warming/serving plates e.g. hors-d’oeuvre warmer or hot plate
    • Large metal tables or work pieces (that can get warm)
    • Heat sealers, heat press, tacking irons, soldering irons with flat tips
    • Kapton flexible heating panels (heaters) and energy source (thermostats, thermocouples, resistance temperature detectors (RTD), thermal fuses, thermistors)
    • Adjustable temperature moderators (Variable voltage resistors/potentiometers/rheostats)
    • Heat temperature thermometer or indicator
    • Localized weights
    • Small platens (that can remain cooler)
    • Large platens (that can remain cooler)
    • Silicon release paper or film
    • Metal spatula and tweezers
    • Heat insulators around metal tools or glove(s)
    • Crepe/crepeline eraser, rubber-cement pick-up
  • Procedure Preparations and Considerations:
    • Prepare a cool platen or other pressing system for the photograph before beginning.
    • Using a dry mount press as the heat source is most effective to reactivate adhesive on smaller photographs (e.g. 8" x 10") and those within the size of the dry mount press platen used.
    • The use of hot platens, such as warming/serving plates, can be the most effective and efficient method of delivering heat to release a dry mount adhesive over a larger area. Heating in large sections can increase speed while minimizing potential distortions during the process.
    • The use of hot air pencils, hair driers, or hot air guns are most effective on small photographs or local treatments. Hot air guns have the potential to scorch the photograph, and can create a great deal of turbulence.
    • Heating a metal tool directly or working on a metal platen or table can be effective for releasing small areas.
    • Know the set temperatures of any heat machine used. The release temperature has to be significantly higher than the set temperature of the dry mount adhesive being released.
    • Use new, clean, dust-free silicone release paper when placing in a press or heating through locally.
    • Gentle mechanical action using a spatula or a palette knife may start releasing the adhesive bond, but the goal is to get the temperature high enough that the photograph releases with minimum effort.
    • Remember that it is important to let the heat do the work. Premature efforts to force-release the adhesive will damage the photograph.
    • Once the adhesive has softened and the materials can be separated, immediately place the materials beneath a cool platen to minimize planar distortion during cooling (otherwise known as "dwell" time).
    • The use of heat to undo a previously heat-mounted photograph will require follow-up clean up with a solvent.

Additional Considerations and Cautions

Cold Mount Adhesives

Contemporary cold-mount systems should be considered irreversible, particularly when used to mount resin coated photographic paper prints. Cold-mount systems do not respond to heat. Solvents cannot get between the carrier and the verso of the RC photographic paper, although solvent will slowly penetrate the thin paper core of the print from the perimeter. However, solvents will take months to evacuate from an RC print, if ever.

"Magnetic" Scrapbook Pages

  • Check the tackiness and discoloration of the exposed adhesive before choosing a removal plan. The less tack and darker the adhesive, the more tenaciously cross-linked and bound the attachment is likely to be. Likewise, the more faded or stained the photograph is along the adhesive lines will indicate level of adhesive penetration.
  • Plastic-backed photographs generally are easier to remove with dry mechanical removal methods than paper-based photographs.
  • Double-sided attachments can be challenging to reduce curl and distortion of the photographs during removal. Some thicker pages can sometimes be split depending on the quality and condition of the paper.
  • Sometimes the attachment can soften with slight warming, then "slicing" the adhesive away with flexible, thin materials such as dental floss or mono-filament fishing line. A single, non-stopping motion is best when separating.
  • Mechanical removal of the adhesive from the back with a crepe/crepeline eraser is sometimes possible depending on how cross-linked the adhesive has become.
  • If the adhesive has hardened, scraping with a scalpel is sometimes possible. Be careful not to skin or chip the back of the photograph or cause plastic distortions from pressure on the back.

Commercial Dry Mounts

Checking carefully along the perimeter of a mounted photograph can sometimes determine type of mounting, including dry mounting materials. Commercial dry mount materials are distinct from thermoplastic or thermo-resin adhesives (sometimes erroneously called "heat-set") and tissue combinations that conservators might employ. A more thorough discussion of dry mounts and laminates is available in the AIC Lexicon: Dry mounting. Dry mounted photographs need not be routinely unmounted. Only the release and separation of commercial dry mount materials are addressed in this section. However, some of the release techniques and concerns are the same or similar to other adhesive products. When unmounting is necessary, choosing the least harmful, least toxic, and least intrusive method of removal is generally preferred.

Damage from Dry Mounts

  • Chemical damage from dry mounting is not observed. In many instances, the dry mount layer has beneficially protected the photograph from a poor-quality mount.
  • Damage from dry mounting usually occurred during the mounting process with incomplete heating, over heating, over pressing, trapped air bubbles, trapped dirt, insufficient dwell time after mounting, etc.

Shellac-based Dry Mount

  • Dry mounts that are translucent, shiny, yellow, or very brown and brittle, are often shellac-based. Shellac-based dry mounts can also have a rubber or synthetic component.
  • Shellac-based dry mount can be carved away, and sometimes shear or peeled off using an acute angle after thinning. Peeling away the tissue works best when the photograph is robust or when the original mounting occurred with low heat. A very slight layer of fiber is sometimes removed in the process that some consider "acceptable". Any potential loss must be weighed against the risks and hazards to the photograph and the conservator from other removal methods.
  • Acetone and ethanol (denatured alcohol and industrial methylated spirits) are the most frequently cited chemicals used to unmount dry mounts, and are most effective with shellac-based dry mount products.
  • Rare, but worth mentioning, ethanol can release a pink dye in Kodak dry mount tissue on photographs mounted in the 1920-30's. The dye stains the perimeter or baryta layers. Origin of this pink dye is still unknown, although one theory is alcohol may release residual red lac dye in the shellac. Both Kodak Type 1 and Thermount tissues were available in this era.

Rubber-containing Dry Mounts

  • Dry mounts that are dull, white or soft-yellow, or waxy, often opaque, thicker looking "papers" are often synthetic or rubber-synthetic combinations.
  • Seal MT5 is known to discolor to yellow-brown tones. Chemical damages to photographic materials have not been attributed from this phenomena.
  • Water, slightly warmed or slightly raised pH, can sometimes release aged, rubber-based dry mounts, even though water does not dissolve the adhesives. Some synthetics may swell enough to allow mechanical separation of the adhesive bond. This method can require extreme hours of immersion that may be inappropriate for many photographic processes.

Synthetic Dry Mounts

  • Dry mounts that are dull, white or soft-yellow, or waxy, often opaque, thicker looking "papers" are often synthetic or rubber-synthetic combinations.
  • Dry mounts that are transparent, clear films and paper-less cores are often synthetic adhesives.
  • Seal Fusion 4000 (earlier versions) that are pure adhesive (without a tissue core) can discolor to a bright yellow-green color around the edges. Chemical damages to photographic materials have not been attributed from this phenomena.
  • Waxy, modern synthetic dry mount adhesives (with or without a pellicle) may release with reheating methods. The longer a photograph has been dry mounted, the harder it may be to unmount with heat as synthetic adhesives are known to cross link as they age. In addition, Fairbrass's (1992) research found that success in reheating to soften the adhesive appeared to be directly related to the extent of light exposure and light aging on an object prior to unmounting attempts.
  • Reheating dry mount tissues can cause the adhesive to be driven into the paper fibers of fiber-based photographs.
  • Both immersion and chamber solvent exposure can be effective in softening up and releasing residual synthetic adhesives.
  • Heptanes, hexanes, naphtha (petroleum ether, benzine) are helpful with waxy dry mount adhesives.
  • Single solvent or mixtures of xylenes and toluene with acetone or methyl ethyl ketone in both immersion and vapor applications can sometimes be effective in releasing modern synthetic dry mount adhesives. Use of the least invasive or toxic chemical combinations are often preferred.
  • Newer dry mount materials generally require high heat to release, followed by removing residual adhesives with solvents.

References

  • Norris, Debbie Hess. “The Unmounting of Historic Photographic Prints: Factors to consider.” Typescript, unpublished, 1993, 4 pp.
  • Orraca, Jose. "Unmounting is Easy...Not!" Typescript, unpublished, 1993, 3 pp.
  • Various, Norris, Debbie Hess (coordinator). Unmounting and Mounting of Photographic Print Materials - Workshop Notes. Workshop in Photograph Conservation funded by the Andrew W. Mellon Foundation. International Museum of Photography and Film at the George Eastman House, Rochester, NY, 13-17 March, 2000.

Dry Mount References by Conservators and Scientists

  • Baas, Valerie. 1985. "Notes on the Removal of Dry Mount Photographic Images and Their Mounts." AIC-PMG.
  • Baynes-Cope, A.D. 1972. The Dismounting of 'Dry Mounted' Photographic Prints, Restaurator 2: 1-3
  • Fairbass, Shiela. 1992. "An Investigation into the Adhesives Used for Dry Mounting (Laminating) paper". Conference papers, Manchester 1-4 April 1992. London: The Institute of Paper Conservation. 91-95.
  • Fairbrass, Sheila. 1994. "Their Nature and Deterioration Characteristics", Journal of the Society of Archivists, Vol. 15, issue, 1:73-81.
  • Herrera, Rosina. 2005. Alfred Stieglitz's Mounting Method for Gelatin Silver Prints - Three Case Studies at George Eastman House Collection. Advanced Residency Program in Photograph Conservation paper. Available at: http://notesonphotographs.org/images/3/36/Stieglitz_mounting_final_for_web.pdf (accessed September 2015)
  • Kellogg, David. 1988. The Permanence of Dry Mounting Tissue and its Effects on Black and White Photographic Prints Under Controlled Humidity and Accelerated Aging Conditions. Unpublished research, courtesy of Jose Orraca and Barbara Lemmen.
  • Lemmen, Barbara. "Inherent vice and Quality: A photograph conservator’s view". Photo Techniques (Mar/April 1997): 46-47.
  • Lyons, Robert. 1984. "The Removal of Dry-Mounted Gelatin Photographic Prints and Their Subsequent Treatment", Presentation at the American Institute for Conservation Photographic Materials Group meeting, Louisville, KY.
  • Reinhold, Nancy. 1991. "An Investigation of Commercially Available Dry Mount Tissues," Topics in Photographic Preservation Washington, D.C.: American Institute for Conservation Photographic Materials Group, 4:14-30.
  • Watkins, Stephanie. 1993. "Origins and Development of Dry Mount", Book and Paper Group Annual, 12: 66-73.
  • Watkins, Stephanie. History and Development of Dry Mount, Handout and presentation at the American Institute for Conservation Photographic Materials Group meeting, Nashville, TN, Friday, 10 June 1994.
  • Watkins, Stephanie. (early 1980 to late 1990's). "The Origins and Development of Dry Mount Adhesives and Papers", includes timeline. Unpublished personal research on dry mounting. See Timeline and product listing.
  • Wilhelm, Henry G. 1993. "Print Mounting Adhesives and Techniques". The Permanence and Care of Color Photographs. Grinnell: Preservation Publishing Co. 367-383. 2


Historic Dry Mount References by Photographers and Industry

  • Adams, A. 1983. "Finishing, Mounting, Storage, Display". The Print, A. Adams and R. Baker. Boston: Little Brown and Co. 145-167.
  • Anonymous. 1906. "Kodak Dry Mounting Tissue". Aristo Eagle (5): 20-21.
  • Keefe, Lawrence E. and D. Inch. 1984. "Dry Mounting". The Life of a Photograph: Archival Processing, Matting, Framing, and Storage. Boston: Focal Press. 65-78.
  • Plikaytis, B. 1997. "Procedures for Dry Mounting Photographs". Photo Techniques (Mar/April 1997): 46-51.
  • Time Life Books. 1972. "The Advantages of Dry Mounting". Caring for Photographs: Display, Storage, Restoration. New York: Time Life Books. 130-133.



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