PMG Section 1.5.3 Glazing and Filter Materials

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Photographic Materials Conservation Catalog
Chapter 1 - Exhibition Guidelines for Photographic Materials

Date: July 2004
Compiler: Stephanie Watkins, 1993-2004
Initiator: Douglas Severson, 1992-1993
Contributors (Alphabetical):
Catherine Ackerman, Nancy Ash, Sarah Bertalan, Jean-Louis Bigourdan, Barbara N. Brown, Ed Buffaloe, Carol Crawford, Corinne Dune, Thomas M. Edmondson, Debra Evans, Julia Fenn, Betty Fiske, Gwenola Furic, Judy Greenfield, Doris Hamburg, Marc Harnly, Pamela Hatchfield, Cathy Henderson, Nancy Heugh, Ana Hofmann, Emily Klayman Jacobson, Martin Jurgens, Nora Kennedy, Daria Keynan, Lyn Koehnline, Barbara Lemmen, Holly Maxson, Constance McCabe, John McElhone, Cecile Mear, Jennifer Jae Mentzer, Jesse Munn, Rachel Mustalish, Douglas Nishimura, Leslie Paisley, Sylvie Penichon, Hugh Phibbs, Dr. Boris Pretzel, Dr. Chandra Reedy, Nancy Reinhold, Andrew Robb, Grant Romer, Kimberly Schenck, Douglas Severson, Tracey Shields, Angela Thompson, Sarah Wagner, Clara Waldthausen, Dr. Mike Ware, Stephanie Watkins, Dr. Paul Whitmore, Faith Zieske, Edward Zinn.

First edition copyright: 2004. The Photographic Materials Conservation Catalog is a publication of the Photographic Materials Group of the American Institute for Conservation of Historic and Artistic Works. The Photographic Materials Conservation Catalog is published as a convenience for the members of the Photographic Materials Group. Publication does not endorse nor recommend any treatments, methods, or techniques described herein.

1.5.3 Glazing and Filtering Materials

1.5.3.1 Considerations of glazing choices including ultraviolet inhibitors and filters
Light, even the visible range, is damaging to materials. Filtering the light source for ultraviolet radiation is desirable but does not eliminate the threat of light damage to a photograph. Wilhelm (1993, 612) suggests that "ultraviolet radiation can easily be reduced by using acrylic sheeting with an ultraviolet filter such as Lucite® SAR UF-3 or Plexiglas® UF-3" on individual framed photographs. Likewise, cases can be made with ultraviolet­inhibiting glazing or an ultraviolet-inhibiting film can be applied to the exterior. Ultraviolet-inhibiting film can be applied directly onto window interiors or exteriors of frame glazing. Film can also reduce heat and glare and protect glazing from breakage and impact, some to the extent of a bomb blast. Lull (1999) believes that ultraviolet absorbing acrylic panels and laminated glass with a poly (vinyl butyral) ultraviolet-absorbing film are better options for reducing ultraviolet radiation than using films on windows. Window films are very thin; they break down faster than the glazing because of sun intensity, and within a few years they can start to separate from the glazing. Ultraviolet-inhibiting filters often come with a 10-year guarantee but seldom last past five years. Films should be considered as short-term applications because of the potential for separation. Predicting how long a filter will last is difficult because viability depends on the light level, length of exposure, and newness of the material. Long-term filtering effectiveness can be monitored by checking periodically with an ultraviolet light meter. Ultraviolet films are available as covers for fluorescent bulbs and should be long enough to cover the ends, where much ultraviolet radiation is emitted (Glaser 1994, 2). Some light fixtures reduce ultraviolet radiation because of the materials used in manufacture of the bulb. Wilhelm (1993, 577,607) has found that Ilford Ilfochromes/Cibachromes do not have an effective ultraviolet-absorbing emulsion overcoat so prints need to be protected from rapid fading by the use of ultraviolet-absorbing glazing such as, Plexiglas®UF-3. In addition, Kodak Dye Transfer® paper prints (dye imbibition process) do not have a UV-absorbing overcoat and can fade rapidly under high UV-conditions. Wilhelm (1993, 577) states that image fading of Ektacolor™/ Fujicolor/ Konica Color/ Agfacolor/ and most other current color print materials is caused primarily by visible light/ not by ultraviolet radiation. Ultraviolet filters do little to increase the life of these color materials/ largely because they are manufactured with an effective ultraviolet-absorbing emulsion overcoat. Many modern photographs contain optical brighteners that fluoresce when excited by radiation within the 397-400 nm range. This includes/ but is not exclusive to/ energy emitted by tungsten light sources. The brighteners are fugitive and will fade and discolor.

1.5.3.2 Recommendations for glazing and filtering materials
Numerous glazing materials suitable for framing photographs are available from common picture glass to polymeric materials. Common picture framing glass reduces some ultraviolet wavelengths/ but has a distinctive green cast. Low-iron glass/ also known as //water white'! glass/ can be used instead/ especially when color accuracy is required. The ultraviolet absorption is similar to regular picture glass. Laminates of glass and ultraviolet absorbing film materials/ such as poly (vinyl butyral)/ silicon or urethane­based coatings/ can absorb 97-99% of ultraviolet radiation below 380 nm. Anti-reflection coatings/ such as silicon dioxide (Si02) and titanium dioxide (Ti02t reflect less than 1% of surface light. Non-reflective coatings and non-glare glass/ made with an acid-etch on one side/ do not absorb ultraviolet radiation/ but can reflect or disperse light. Non-glare glass is not recommended for display of original material as the glass must be in direct contact with the photograph to appear sharp. Plastic glazing suitable for photographs made from acrylic/ cast and extruded including poly (methyl methacrylate)/ and poly (carbonate) have the advantage over glass glazing of lighter weight and resistance to breakage upon impact. Weight considerations are important when displaying large framed or oversized photographs or designing traveling and plastic sheets are generally less prone to breakage during shipping or handling. Acrylic glazing is available with ultraviolet inhibitors, abrasion resistance, and anti-reflection coatings. Poly (carbonate) sheets have been used in exhibitions of large/ oversized photographs/ although poly (carbonate) sheeting generally scratches easier and yellows faster than acrylic sheeting. Some poly (carbonate) brands offer an abrasion­resistant surface. Wilhelm (1993/ 577) recommends the use of glass (or clear Plexiglas® G if travel is indicated) rather than ultraviolet-inhibiting plastics to avoid color shift. Acrylite® OP3 and Plexiglas® UF5 have less of a yellow color shift than other plastic sheets used for glazing. "Water-white" or low-iron glass eliminates the problem of color shifts apparent in other glazing structures and has similar ultraviolet filtering effectiveness as other picture framing glass. However/ it is weaker/ so thicker sheets or laminates should be used (Phibbs 1997) which would also increase weight. Instead of using plastics/ Wilhelm (1993/ 607-608) prefers to filter the illumination source to reduce or eliminate ultraviolet light. The Polaroid Corporation (1983/ 33) recommends for Polaroid® photographs acrylic glazing such as Acrylite® GP/ Lucite® UF-4/ Acrylite® OP-2/ Lucite® UF-3/Plexiglas® UF/ or glass. Dichroic (two-color) or interference filters are made of heat resistant borosilicate glass and can be used in conjunction with light fixtures to absorb 99% of ultraviolet radiation below 400 nm. The color of the filter varies with transmitted or reflected light/ and while light intensity is diminished/ the dichroic filter does not fade.

1.5.3.3 Care and maintenance of glazing and filter materials
Wilhelm (1993/ 523) recommends water-based nonionic detergents and warm water for cleaning glass. Many commercial brands of glass cleaner contain ammonia/ which can damage dyes in color photographs. Schott AG product literature (2000) recommends the use of a damp chamois cloth to reduce static and dust. Thorough rinsing of cleaning agents, detergents, and soaps is recommended. Mild soap and water cleaning may be best for plastics, also. In the past, companies producing plastics have recommended, alcohols (ethanol, methanol, and isopropanol) and mild acetic acid (vinegar) for cleaning their products, but these materials can cause crazing and cracking of rigid plastic sheets. Some companies now recommend naphtha and similar non-aromatic hydrocarbon formulations for cleaning plastic, but although these solvents are relatively safe for poly (methyl methacrylate), it is risky to use them on poly (styrene) or poly (carbonate). Personal protection equipment and suitable ventilation are needed for the worker to safely use these chemicals. Image Permanence Institute's acid-detection strips can be useful in determining if plastics (sheeting or exhibit cases) have been previously cleaned with acetic acid.

1.5.3.4 Commercial products for glazing and filtering
WARNING/ CONSUMER BEWARE:

  • The composition of proprietary materials is subject to change without notification.
  • With the passage of time, the information provided here will become outdated.
  • Product information is provided as a guide only and is not an exclusive list.
  • Each application is unique. Evaluate materials for suitability before use.

Glass and glass laminates: CHB Industries: Hardglass™ Denglas: UV laminated Safety Glass, Anti-reflective, Quartzkote, Water-white Sandel: Crystalview, Satinview, Preservation Clear, Superior Clear, Schott Glas: Amiran® series, TN (thin) Tru Vue: Conservation Series™, Clear, Museum, UltraClear AR, Reflection-Free, Vision: Laminated Glass Zuel: Photo Clear™ UV 100, Image Perfect®,

Acrylic sheets: AtoHaas: Plexiglas® series: G, MC, UF-3, UF-4, UF-5 CYRO: Acrylite® series: GP (general purpose), AR (abrasion resistant) Dupont/ICI: Perspex® series: VE Dupont: Lucite® series: UF-3, UF-4; UF-5, SAR (super abrasion resistant) SD Plastics: Polycast Tru Vue: Optium™ Museum Acrylic, Reflection-free Acrylic

Poly (carbonate) sheets: CYRO: Cyrolon® ARl, AR2 GE Plastics: Lexan®, Margard MR5000®

Filters for window interiors and glazing exteriors: Madico LTD.: Saft-ee Shield F CLS-200-X, CL-400-X 3M: Glass Safe®, Scotchtint®, and Scotchshield®

Dichroic (two-color) or interference filters: Bausch and Lomb: Optivex™ ultraviolet glass

1.5.4 Matting, backboards, and support materials As of publication, conservators are divided on whether alkaline or neutral support materials should be used with photographic materials.

1.5.4.1 Considerations
ISO 18902 (2001) recommends that enclosures and supports used with photographic materials, whether black-and-white or color materials, have an alkaline reserve. This standard replaces ANSI IT9.2-1991, which stated only that support materials should be free of acids and peroxides. Materials with an alkaline reserve are generally considered safe for contemporary silver gelatin, resin coated prints as long as the materials do not remain in contact with the gelatin surface (Burgess and Leckie 1991 100). Initially, it was felt that alkaline boards would be detrimental to albumen prints (Reilly 1986t but more recent research at the Image Permanence Institute seems to indicate "that calcium carbonate buffering [on paper products and boards] is not by itself a major threat to albumen prints" (Reilly, quoted in Ware, 1994, 58). Acidic housing materials can cause changes in color dye materials and weakness in support materials. Moor and Moor (1992, 197) believe that inert and compatible support materials must be used because photographic emulsions are sensitive to strong alkaline and acidic materials. Some conservators recommend that housing materials with 100% rag content without alkaline reserves should be used, especially in conjunction with photographic processes that are stabilized at an acidic pH or are composed of materials known to be chemically affected by strong alkali conditions. Examples include chromogenic and dye imbibition (e.g. Dye Transfer®) prints, cyanotypes, Vandyke brown, platinum, and palladium prints. Materials with alkaline reserve should not be used with daguerreotypes or cyanotypes. The alkaline salts in paper products have been shown to cause tarnish films, corrosion, and etching of the daguerrean surface (Barger and White 1991, 173,203). Ware (1999, 131) notes, "It is now generally advised that cyanotypes should not be mounted on, or stored in buffered materials [paper boards made with calcium carbonate] in case they suffer alkaline deterioration." Research has proved that alkaline solutions can destroy Prussian blue, ferric ferrocyanide, the image material for cyanotypes. Another conclusion is that salted paper, photogenic, Vandyke brown, platinum, and palladium prints do not have a protein binder (susceptible to attack by strong alkali; specifically, calcium carbonate is potentially hazardous to gelatin) and the image material is attached to paper (susceptible to attack by strong acid and benefiting from a mildly alkaline environment); therefore, mildly alkaline (below pH 9.0) housing is beneficial and desired (Ware 1994, 58). Either way, both neutral and mildly alkaline materials are likely to be more alkaline than the print papers. The photographic emulsion can be isolated from the back of the window mat by attaching an undermat of suitable barrier material as appropriate to each photographic type or using thin V-shaped edge strips along the perimeter of the back of the window opening (Phibbs 1997). For cyanotypes, Ware (1999) additionally recommends deep mats that provide an air pocket, as air is necessary to offset fading of cyanotypes while on display. High humidity and flooding situations that release alkali from the housing materials are of concern. However, if either situation occurs, damage from released alkali may be less of a problem than the softening of photographic emulsions, bleeding of writing, and potential for the establishment of mold (conidia). The adhesive used to laminate the plies of mat board should be considered when choosing. Plies adhered with starches or dextrin may be preferred for use with photographic materials over plies adhered with poly (vinyl acetate) emulsion adhesives given recent and ongoing off-gassing problems. Ammonia has been used to neutralize acetic acid in poly (vinyl acetate) emulsion adhesives, so noticing an ammonia odor can indicate its use as a ply adhesive in a laminate board. Neutralizing the acetic acid can be accomplished by adding alkaline materials, such as chalk, to the poly (vinyl acetate) emulsion adhesive. The cut, beveled edges of the window may be softened with sandpaper (such as on an emery board), with a nail file covered with industrial diamond, or with a Ieflon® spatula. Phibbs (1997, 13) prefers the industrial diamond covered nail file, as "sand paper or emery boards may leave grit on the bevel, contaminating it." A softened edge will reduce potential cutting of a soft emulsion surface.

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