PMG Section 1.5.4 Matting, Backboards, and Support Materials

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Photographic Materials Conservation Catalog
Exhibition Guidelines for Photographic Materials

Date: July 2004
Contributors to WIKI version: Your name could be here!
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 Jürgens, 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 Pénichon, 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 von 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.

Matting, backboards, and support materials

As of publication, conservators are divided on whether alkaline or neutral support materials should be used with photographic materials.
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 1986) 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, etched crystal, or with a Teflon® 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.

Recommendations for mat boards and backing materials

Materials passing the Photographic Activity Test (PAT), ISO 14523:2000 (formerly ANSI IT9.2-1991 and ANSI IT9.16-1993), can be recommended for exhibition and storage use with photographic materials. The PAT tests were originally designed to test quality and suitability of paper boards used with silver photographic images and were updated in 1993. to include color and diazo (microfilm). The PAT tests materials by manufacturing batch, not recipe or type.

Commercial paperboard products
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.

According to Brower (1993, 414), boards that have advertised as having passed the PAT (pre-1993) are:

• Light Impressions Westminster TM100% cotton rag
• Light Impressions Exeter™ Conservation Board
• Light Impressions Non-buffered 100% cotton rag

The James River, Monadnock, Parsons, Rising, and Strathmore paper companies manufacture and supply virtually all the matting and mounting boards available in the United States. Crane Paper Company supplies the Crescent brand. Brower (1993, 410) lists the following products as 100% cotton fiber boards with an alkaline-reserve suitable for use with photographic materials:

• Andrew-Nelson-Whitehead (ANW)-Crestwood Lenox
• ANW-Crestwood Gemini
• Archivart Extra White Custom Papers Group Inc. White
• Miller Shell White
• Rising Warm White, Bright White, Antique
• Strathmore Natural Strathmore White

The following 100% cotton fiber boards without an alkaline-reserve may be suitable for photographic materials, especially for color materials:

• Atlantis 100% Cotton Museum Board (TG Offwhite), (initially called Heritage Museum Board IG Offwhite, 1985)
• Parsons Brite White Photographic Museum Board (adhered with a poly(vinyl acetate) adhesive) (Phibbs 1997)
• Rising White Photomount Museum Board
• Atlantis 100% Cotton Museum Boards are specifically manufactured in the United Kingdom for photographic materials. "The 100% cotton boards are sized with alkyl ketone dimer sizing agent and 'lightly' surface-sized with a modified non-ionic farina starch, and have a pH of 7.0", without an alkaline reserve. The board plies are laminated with a V.A.E [ethylene vinyl acetate emulsion] polymer adhesive which contains no plasticizer and is about pH 7.0" (Brower and Wilhelm 1993, 453, 478).

Brower and Wilhelm (1993, 453) found the following 100% cotton colored alkaline reserve boards to have "superior light fading stability" and be suitable for use with photographic materials:

• Custom Papers Group, Inc. (formerly James River) Museum Board (Ivory)
• Strathmore Museum Board (Brown, Creme, Gray, Green, Natural and Black, recommended when a non-colored undermat is provided)
• Boards made with activated carbon or synthetic zeolite (silicate particles) internal molecular traps, such as MicroChamber™ (introduced by Conservation Resources in 1992) and ArtCare™ (introduced by Nielsen & Bainbridge in 1995, using a patent leased from Conservation Resources)/ remove or reduce the amount of acetic acid/ nitrogen oxide, and sulfur dioxide present in the immediate environment (Rempel 1996). These materials can be used for framing and exhibition cases. ArtCare™ is made of alpha-cellulose with the addition of alkaline reserve(s) and synthetic zeolites for a white core. According to the Conservation Resources literature distributed in 1997/ some MicroChamber™ materials have natural (activated charcoal) and synthetic zeolites with an alkaline reserve in an alpha-cellulose free of lignin and sulfur. The charcoal side can be powdery/ producing black marks and grit.
• Lig-free Type II Boxboard (a thin sheet of polyester film laminated between a sheet of lignin-free, alkaline-buffered wood cellulose boxboard on one side and white, non-buffered, near neutral [pH], lignin-free paper on the other, attached with a poly [vinyl acetate] adhesive) and anodized aluminum are recommended as good backing materials (Wilhelm 1993, 520).
• Corrugated poly (ethylene) sheets (Corrulite®), double-walled poly(propylene) (Coroplast™, Core-x™), and double-walled poly (carbonate) (Macorlux™) may prove to be acceptable. Sheets made of high-quality poly(propylene) without antistatic, ultraviolet inhibitors are available. The material is prone to static, therefore attracting dust, and has the disadvantage of sharp edges after cutting. It can be used as a backboard in frames and can function as a water barrier if sealed around the perimeter into a frame. A batch of Corroplast™ and Corrulite™ tested by the Library of Congress Research and Testing Division in 1997 passed the Photographic Activity Test (PAT).

Materials deemed suitable for display with Polaroid® prints by the Polaroid Corporation (1983, 33) are:

• 100% cotton rag museum board
• photographic and archival papers
• poly (ethylene)
• polyester sheeting and sleeves
• glass, porcelain, and acrylic plastics

Also cited by the Polaroid Corporation (1983) is the suitability of cellulose acetate. However, research conducted since 1983 suggests this material is unacceptable for use in display conditions. Not recommended as backing materials are corrugated cardboard, gray chipboard, strawboard, binder's board, plywood, Masonite®, and extruded poly (styrene) foam laminates such as Fome-Cor® (Wilhelm 1993, 519). "Cardboard backing material should be avoided as this material can emit harmful fumes. Plywood and pressboard should be avoided, as they contain potentially harmful glues" (Polaroid Corporation 1983, 33).

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