PMG Section 1.4.3 Standards, Guidelines, and Recommendations for Air Quality During Exhibition
Photographic Materials Conservation Catalog
Exhibition Guidelines for Photographic Materials
Date: July 2004
Contributors to Wiki version: Your name could go 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.
Types of Pollutants
Photographic materials are sensitive to even trace amounts of airborne pollutants. Pollutants damaging to photographic materials include, but may not be limited to (alphabetically), acetic acid, ammonia, formaldehyde and formic acid, nitrogen oxides, ozone, peroxides, and sulfur compounds such as hydrogen sulfide and sulfur dioxide. Particulates damaging to photographic materials include, but may not be limited to (alphabetically), conidia (mold spores), dirt, sand and sea salt, soot, tar and nicotine smoke from cigarettes, cigars, and pipes.
Standards, guidelines, and recommendations
Pollutants are not considered safe at any level. The goal is to get levels down as low as possible with the available technology. Accuracy of instrumentation is critical to monitoring. It is unrealistic to set any limits that cannot be measured with available equipment. For example, all of the following recommendations by Thomson (1986) are within error ranges of most contemporary instruments.
The recommended limit for carbon dioxide (CO2) level is less than 4.5 μg/m3 (micrograms per cubed meters) in archival storage areas (Mathey et al. 1983).
The recommended limit for ozone (O3) level is less than 2 μg/m3 in general museum collections (Thomson 1986, 268). A level of less than 25 μg/m3is recommended for archival storage areas (Mathey et al. 1983). The Library of Congress, Washington, D.C. proposes levels of less than 0.94 parts per billion (ppb). However, general instrument background noise levels inside can be as high as approximately 10 ppb. If the inherent noise level of the machine can be brought down to 5 ppb, monitoring is possible.
Sulfur dioxide (SO2) is measurable at 2-5 ppb. Recommended limit for sulfur dioxide level is less than 1 μg/m3 in archival storage areas (Mathey et a1. 1983). Less than 10 μg/m3 level is recommended for general museum collections (Thomson 1986, 268).
The recommended limit for levels of nitrogen oxides (NOx) is less than 5 μg/m3 in archival storage areas (Mathey et al. 1983). A 10 μg/m3 Iimit was recommended for general museum collections (Thomson 1986, 288). Ozone (O3), sulfur dioxide (SO2), and hydrogen sulfide (H25) are easily removed with activated carbon filter banks, but nitrogen oxide (NO2) is not. Rather than place unrealistic limits on maximum levels of acceptable NO2, it is better to set lower limits for the other gasses that are more easily removed.
Detection of Pollutants
General and Multiple types of Pollutants
- The Photographic Activity Test (PAT), ISO 14523:2000 (formerly ANSI IT9.2-1991 and ANSI IT9.16-1993), is useful for determining the suitability of fibrous and plastic materials for use in cases. The PAT tests materials by manufacturing batch, not recipe or type. Colloidal silver film is placed in between the materials to be tested. The package is placed in an oven, and heat and humidity are cycled for 14 days. Upon removal, if the colloidal silver film is spotted significantly, if the gelatin is discolored yellow, or if a change of density has occurred, the material fails the test.
- Research by Edith Weyde and associates (1972) indicates that colloidal silver test strips can be placed in collections to monitor harmful air pollutants. A strip of colloidal silver (grain size less than 30 nm) is placed in the area to be tested. The test is time dependent. The faster the strips darken, the more pollutants that are in that environment. Darkening occurring in a few weeks is considered to indicate higher risk; darkening occurring over a few years is considered to indicate lower risk. The identity and source of the possible pollutants are not established with this testing method. Additionally, this test is very sensitive, and oxygen and moisture in air have been corrosive enough to attack the silver strips.
- The Oddy test tests for the presence of volatile, corrosive gases by monitoring metal corrosion. The test is relevant to photographic materials because many final image layers are combinations of metallic particles. The sample material to be tested and cleaned, abraded, and scratched coupons of copper, lead, and silver are artificially aged together at 140°F (60°Ct 100% humidity for a minimum of a week (28 days preferred). The amount of corrosion developed is compared to control strips. Subjective interpretation of corrosion amounts determines how the material is classified (Green and Thickett 1994, 8; Richard et al. 1991, Section 8). Problems with the Oddy test are that it takes considerable time to get the results, and the assessments are subjective. Strict controls must be maintained during testing to achieve comparable test results. Recently, there has been controversy regarding whether the test is sensitive enough to detect corrosive gases at the levels at which photographic materials are at risk for damage. Revision of the test may control or limit inherent variables and resolve some of these concerns. To improve on the Oddy, an electromechanical method for testing corrosive volatile materials has been researched by the University of Delaware Art Conservation Department in collaboration with the National Park Service Division of Conservation, Harpers Ferry Center (Reedy et al. 1998).
- Drager rapid detection tubes "can detect the presence of several types of gases, such as organic acids, hydrochloric acid, and formaldehyde. The detection tubes have a lifetime of around two years" (Tetreault 1992, 3).
- Solid Phase Microextraction (SPME) techniques used in conjunction with gas chromatographs (GC) can detect very small sample sizes of various pollutants. Janusz Pawliszyn at the University of Waterloo in Ontario, Canada invented SPME in the early 1990s. "The SPME fiber is coated with a liquid (polymer), a solid (sorbent), or a combination of both. The fiber coating removes compounds by absorption in the case of liquid coatings or adsorbtion in the case of solid coatings. The SPME fiber is then inserted directly into a gas chromatograph for desorption and analysis" (Sigma-Aldrich 2004). SPME is solvent-free, reusable, and fast to use when a gas chromatograph is available.
Organic acids such as acetic and formic acids
- The iodide/iodate test identifies the emission of organic acids such as acetic and formic acid. A solution of iodide/iodate is encased along with the test material at a temperature of 140°F (60°C) for 30 minutes. A blue color in the solution confirms the presence of volatile acids (Green and Thickett 1994, 10; Zhang et al. 1994).
- PH indicator paper can be adapted to test for acidic volatile gases using inexpensive materials usually found in a conservation lab. The acidity of the emissions from a material is measured. Glycerin (or glycerol) is applied to a pH indicator paper (pH 4-7 range is most practical). The glycerin-impregnated pH paper must be stored in a well sealed container until use. Within an airtight container, suspend the material to be tested and the indicator paper or place both on an inert clean surface during testing lasting for 24 hours. Compare the results against the control pH indicator. The color of the pH indicator changes with the amount of acid absorbed by the solution" at a particular temperature (Tetreault 1992).
- Acid-Detector (A-D) strips (bromocresol green) are a nondestructive test that determines the presence of acetic acid (pH range 3.8-5.4). The sample and strip are placed in a relatively sealed environment (such as a ziplock-style plastic bag). After 24 hours, the extent of color change indicates the level of acetic acid present (Image Permanence Institute test kit 1995). While specifically designed to detect acetic acid off-gassing of photographic film, A-D strips have been used to test for the presence of "other acids released by adhesives, papers, textiles, wood products, and plastics for screening conservation and exhibition materials" (Nicholson and O'Loughlin 1996b).
Chlorine, bromine, or iodine inorganic compounds
The Beilstein test will detect the presence of chlorine, bromine, or iodine in organic compounds. Clean copper is heated and touched to the sample material to be tested, and the sample is burned in a flame. If the flame turns blue-green, chlorine, bromine, or iodine is present in the sample and the material is unsuitable for use with photographic materials. Certain compounds such as quinoline, urea, and pyridine derivatives give misleading blue-green flames owing to the formation of volatile copper cyanide with this test method, but these materials are generally not considered safe for photographic materials either (Green and Thickett 1994, 9).
The chromotropic acid test confirms the emission of formaldehyde. This test can be used to determine the suitability of housing and construction materials for use on exhibit, not on original photographic materials intended for display. Personal protection equipment and caution are required when performing this test. Chromotropic acid (4,5dihydroxynaphthalene-2, 7-disulphonic acid) in concentrated sulfuric acid is enclosed with the sample to be tested and heated at a temperature of 140°F (60°C) for 30 minutes. Yellow solutions indicate no formaldehyde; violet blue indicates formaldehyde (Zhang, et al. 1994). Other tests exist but require more sophisticated apparatus. For those with access to an analytical laboratory, see the test methods used by Hatchfield and Carpenter (1987) and Hatchfield (1999).
- The azide test detects the presence of reducible sulfide in fibrous materials. This test can be used to test the sulfur content of display materials. Personal protection equipment and extreme caution are required when performing this test. A solution of sodium azide, iodine, and ethanol are applied to fibers on a glass slide under a microscope and observed for about two minutes. Sulfur azide and iodine form nitrogen gas when in contact with sulfur. Particulates on the sample can interfere with the test (Daniels and Ward 1982).
- Sulfide "traps" (3M's Oxidation Arrest Paper) have been used to detect and remove airborne sulfides from enclosed daguerreotypes (Mustardo 1986).
- The diphenylamine spot test detects the presence of cellulose nitrate and can be performed on materials used in housing of photographic materials or construction of exhibition spaces. The spot test is done with a solution of 0.05% diphenylamine in 90% sulfuric acid and water. Personal protection equipment and caution are required when performing this test. The solution should be made in a fume hood. It is highly corrosive and should be stored in glass bottles with plastic caps resistant to sulfuric acid. A tiny sample is placed on a glass or white porcelain surface. A single drop of reagent is placed on the sample while ensuring that the dropper does not touch it. A blue-violet stain indicates the positive presence of cellulose nitrate. All other scenarios (no color change, orange, yellow, brown, or green) indicate a negative result. This test is very sensitive so care must be taken when gathering a sample. Even trace amounts of residual adhesive, for example, will test positive (Williams 1988).
- Cresol red (o-cresolsulphonephthalein) or Cresol purple solutions applied to filter paper have been used to detect the presence of nitrogen dioxide from decomposing cellulose nitrate (Fenn 1995b, Hatchfield 2004). See also Zhang et al. (1994) and Hatchfield (2002).
Reduction of airborne pollutants
General corrosive gasses
In general, many techniques for reducing and removing airborne pollutants make use of adsorbents and scavengers.
- Activated carbon/charcoal has been found to remove the widest range of pollutants (Grosjean and Parmar 1991). Carbon is a true "buffer" in that it will absorb pollutants until full, then will re-emit what has been stored. Activated carboni charcoal filters should be changed at pre-established intervals before the material is exhausted of the capacity to absorb. As there is no indicator to detect saturation of charcoal/ carbon, a small number of potassium permanganate pellets can be added. When the potassium permanganate turns from purple to gray, it is time to change the filter. As potassium permanganate and charcoal do not adsorb the same chemicals at the same rate, mixing the two to achieve a visual indicator should be taken as a general, not a specific indicator.
- Activated carbon is an example of a natural zeolite molecular trap. Synthetic zeolites can be designed to trap specific molecules by forming chemical bonds with volatile materials. Conservation Resources Incorporated's Microchamber® product line of paper and board materials are a combination of alpha-cellulose pulp, synthetic zeolites (such as crystalline alumino-silicates), and alkaline reserve of calcium carbonate. Some products are manufactured with activated carbon layers. The manufacturers claim the materials will remove acetic acid, formic acid, phenols, aldehydes, hydrogen peroxide, ozone, sulfur dioxide, hydrogen sulfide, carbon disulfide, nitrogen oxides, ammonia, and formaldehyde (Rempel 1996, product literature 1995). Conservation Resources Incorporated has leased the technology to Nielsen & Bainbridge, which manufactures Alphamat® ArtCare™ product line of mat boards. The boards consist of alpha-cellulose pulp, synthetic zeolites, and alkaline reserves (Nielsen & Bainbridge product literature 1996). While these materials seem wonderfully promising and potentially better than currently available paperboard with alkaline reserves, time and natural aging have not yet confirmed whether they will live up to the extent of the manufacturer's claims.
- "Activated Carbon Cloth" contains 100% activated carbon that is advertised "to absorb contaminants such as acetic acid, but will also remove odors from deteriorating organic objects and reduce water vapor, thereby reducing humidity" (University Products advertising literature 1999).
- Mead Company also produces a carbon paper that is 50% carbon by weight. Other products such as activated charcoal cloth and 3M's silver protector strips have been used to remove nonvolatile chlorides from within metal decorative arts cases (Hatchfield 1996).
- Potassium permanganate (KMn04) (4%) impregnated in activated alumina, PurafiITM, is effective in reducing gaseous pollutants in frames and cases (Grosjean and Parmar 1991). A change of color from purple to black indicates that absorption capacity has been reached, and the materials will not re-emit pollutants unlike carbon. PurafilTM is available in a variety of forms, such as pellets, granules, papers, and boards (Hatchfield 1996).
- "Corrosion Intercept" film (molecular copper) can be an optimum barrier film (double foil outer layer with molecular copper interior). It tested better than Marvel Seal 360™ in initial tests at the Museum of Fine Arts, Boston, in 1996 (Hatchfield 1996). The material turns black when the copper is exhausted. It may also have some antifungal capacity, although this is not yet quantitatively proved. It has been used in enclosure designs for daguerreotypes.
- "Tarnish Inhibitor Capsules and Plastabs" are advertised as "corrosion inhibitors for ferrous, non-ferrous metals, and glass-plate negatives. Proprietary formula. Effective life is approximately one year" (Conservation Resources catalog 1995).
Kodak's molecular sieve "Acid Scavenger" desiccant is advertised for use with triacetate, polyester, and nitrate film bases with black-and-white or color emulsions. "The material is stored in a semi-permeable packet of Tyvek™ which allows vapors to be easily scavenged and contained" (Kodak product literature, n. d., ca. mid-1990s). The manufacturer claims the product reduces the moisture in an enclosed case, thus potentially slowing down chemical processes such as the formation of acetic acid (vinegar syndrome) and reducing the possibility of fungal growth. The manufacturer also claims the product reduces oxidation reactions from peroxides and ozone.
- Zinc oxide pellets (lCI's Puraspec 4020) have helped lower hydrogen sulfide concentrations (and thereby reduced tarnishing on silver artifacts) when placed in an exhibition case in the British Museum (Green and Thickett 1994). A solid granule adsorbent (Miracle Sac™) has been used to lower concentrations of sulfides that cause tarnishing of metal artifacts in storage.
- Thomson (1986, 158) reports that copper-impregnated activated carbon (Sonoxcarb™) filters are effective in reducing levels of pollutants particularly sulfur dioxide.
- 3M's Oxidation Arrest Paper, developed by Robert Wieman in the mid-1970s, , with an active ingredient of activated charcoal impregnated into paper, can remove ambient sulfides within cases. 3M's silver protector strips have been used in metal decorative arts cases at the Museum of Fine Arts, Boston, since the 1980s.
According to Hatchfield (1996), vapor phase inhibitors are not effective in removing amino nitrates, which are very difficult to remove.
It is known that ferns, such as spider plants, help break down gases such as formaldehyde, but using plants in exhibition spaces should be carefully considered. Plants can produce higher humidity levels and attract insects, although potential insect infestations can be mitigated through a consistent integrated pest management program.
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