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Methods for testing construction materials, housing materials, etc., before use near museum or archival objects

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Many different material test methods has been suggested over time in the conservation/preservation literature.

Most of the current tests are quite simple to perform. Many of them are chemical spot tests or designed in such a way that a material is tested for its effect on some sort of detector during a short time in an extreme climate (high temperature and RH).

Below is a list of the most common tests. I've written a short description for each, but please consult the literature for all details, as I have only abstracted the descriptions here.
And be aware that passing a test is no guarantee that a material really is safe for use with museum objects.

Often the various tests do not distinguish between the use of a material in direct contact with a museum object and the placement of that material somewhere near the object (although not touching it). When designing your own test program, keep in mind whether or not the materials in question are intended for use in direct contact, as the reactions and their effect may differ more or less, depending on whether a pollutant can migrate directly from one material to another, or must travel through the air to reach the object.

List of test methods:

Metal coupons used as detectors

There are many references to the use of metal coupons as detectors for corrosive vapors. The idea is to place a coupon in the same environment in which the museum object(s) will later be placed (e.g. a showcase), the coupon being of the same type of metal as the object. If, for example, a silver coupon rapidly tarnishes after being placed in a new show case, don't use that showcase for your precious silver coin collection. :-)
    Evaluation of this kind of testing should be done with a certain amount of reservation as the test cannot be considered very accurate. For example, there can be a difference in the level of corrosion that will occur on different alloys of the same metals, which is why the coupon method could give you a false sense of security. A refinement of the coupon method is to accelerate the speed of corrosion by raising the RH and temperature ("The Oddy Test").

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The Iodide-Azide Test for the presence of sulphides

This spot-test will detect presence of reduccible sulphides in a material. Just a small bit of test material is enough, as the test can be caried out under a microscope. Place it in a microscope slide glass with a drop of a solution prepared from: 3 g sodium azide dissolved in 100 ml 0.05M iodine solution + 3 ml methylated spirit. If sulphides are present, a reaction between sodium azide and iodine is catalysed, and nitrogen gas will be given off as small bubbles.
The reaction is: 2NaN3 + I2 -> 2NaI + 3N2 (gas).

Read the full description in V. Daniels & S. Ward (1982): "A Rapid Test for the Detection of Substances which will tarnish Silver", Studies in Conservation, 27, pp. 58-60.

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The Beilstein Test for the presence of chlorides (in plastics)

This simple test will very clearly detect if materials, often plastics, contains chlorides. Place a bit of the test specimen on the end of a copper wire, and place the wire over a gas flame. If the test material contains chlorides, the flame will turn green. (Actually any halogen will colour the flame, however, iodine and bromine will make a more blue flame). Be sure to glow the wire to red-hot before you do the test in order to remove potential dirt, salts, etc., which can give misleading results.
    This test is perfect for determining if plastic-sleeves for the housing of coins, banknotes, photographs, comics, etc., are made of poly-vinyl-chloride. PVC should never be used for housing archival materials, because of the potential for plasticizers to bleed.
    The test is described in full in the CCI Notes 17/1, (bibliography). You can also se pictures of the test performed at The University of Akron's Organic Teaching Laboratory Homepage.

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pH measurement

Measuring the pH of a material will give you a clue about its acid content. One way to measure pH is the cold extraction method as standardized by the Technical Association of the Paper and Pulp Industry TAPPI, for paper products: (I see no reason why this can't be used on other materials as well). 1.00 gram of the test specimen must be ground, and poured into 70 ml of destilled water. Wait one hour, and measure the pH of the water with an accurate pH-meter (pre-calibrated, off course).

The defination of the unit pH is: log10 1/[H+]. (Where [H+] is the number of moles of hydrogen ions in one cubic decimetre of a solution). If the pH of a solution is less than 7 it is acetic, if pH = 7 it is neutral, and if pH is above 7 it is alkalic.

If a solution has a pH under 4, the presence of weak or strong acids can be determined. This is done by calculating the difference in the pH of the soultion and the pH of the solution diluted by 10 parts. This difference in pH will be less than 0.7 if the solution consists weak acids only (or strong acids weakend with alkalies). If the difference is more than 0.7, the solution consists of strong acids. The difference cannot be more than 1.0.

For more about measuring acidity, see also: Jean Tétreault (1992): "Measuring the Acidity of Volatile Products". Journal of the International Institute for Conservation - Canadian Group (IIC-CG), vol. 17. pp. 17-25. Also online at the CCI web site.

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The Phloroglucinol-HCl Test for the presence of lignin (paper products)

Lignin is a natural component of wood and will be found in paper made of wood pulp unless it has been chemically removed. Lignin makes paper acidic, causing it to become discolored and brittle, and is therefore undesirable in archival materials, whether documents, books, or materials for conservation repair or housing. A simple spot test will detect the presence of lignin. The reagent is made from 1.0 gram phloroglucine + 50 ml absolute ethanol + 50 ml conc. HCl + 50 ml destilled water. One drop placed on the test material will turn red/purple is lignin is present. Actually a few paper fibres will be sufficient material, and the reaction can then be observed under microscope.

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The Oddy Test

Suggested by Andrew Oddy of The British Museum in 1973, this test is probably the most often cited materials test method in the museum litterature.

The idea of the test is to expose three samples of the material in question to three metal coupons: one lead, one copper, and one silver. These coupons act as detectors of the formation of corrosion during exposure.
    The setup requires that one metal coupon and one material sample be enclosed in a test tube or flask, together with 1 ml of pure water (to give a high relative humidity). The test tube shall be closed completely airtight. The metal coupons may not touch the test specimen. The tests condition require heating to 60°C for 28 days. Some also suggest that the test tube containing the lead detector should be flushed with CO2 to speed up possibly corrosion. Each test should be done twice for greater certainty. Also, a blind test should be done for each detector type (a test tube with a metal coupon + water only). The criteria for pass or fail is a visual evaluation. In order to pass the test, a material should cause no more corrosion on any of the metal coupons than caused by the reference blind test.
    Corrosion of the different metals gives, by the way, a clue as to which gasses the materials emit. Silver is corroded by sulphur-compounds, lead is corroded by organic acids and aldehydes, and copper by chlorides, oxides and sulphur-compounds. Other gasses will also cause various types of corrosion.

It has be suggested that also other types of metals could be used as detectors, eg. zink. (Lorna R. Green & David Thickett (1993): "Modern Metals in Museum Collections"...). The original reference on the Oddy Test is the 1973 article by Andrew Oddy. Especially researchers at The British Museum have since published much about the test method and added improvements to it: Susan M. Blackshaw & Vincent D. Daniels (1979); Lorna R. Green & David Thickett (1990, 1992, 1993x3, 1995). Please check the bibliography for the full references.

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The Chromotropic Acid Test for the presence of aldehydes (formaldehyde)

This test and the The Iodide-Iodate Test are often refered to as time-saving alternatives to the Oddy Test.

A solution of chromotropic acid (1% w/v) is prepared in conc. sulpuric acid (97%). This solution should be used at once. The solution is yellowish, but will turn blue if exposed to aldehydes.

Approximately ten drops of the solution is placed in a small reaction dish, inside a conical flask. In addition, 2 g. of the test specimen is placed in the flask, without touching the liquid solution. Please see the litterature references for the exact design of the setup.
The bottle is closed airtight and heated to 60°C for 30 minutes. If the solution turns blue, the tested material is emitting aldehydes.

A full description is given in: Jinping Zhang, David Thichett & Lorna Green (1994); and L.R. Lee. & D. Thickett (1996) (Bibliography).

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The Iodide-Iodate Test for the presence of volatile acids

This test and the The Chromotropic Acid Test are often refered to as time-saving alternatives to the Oddy Test.

Three solutions are made: potassium iodide (2% w/v), potassium iodate (4% w/v), and soluble starch (0.1% w/v). Two drops of each solutions are mixed in a small reaction dish. The blend is colourless, but will turn blue if exposed to acids.

The dish is placed inside a conical flask. In addition 2 g. of the test specimen is placed in the flask, without touching the liquid solution. Please see the litterature references for the exact design of the setup.
The bottle is closed airtight and heated to 60°C for 30 minutes. If the solution turns blue, the tested material is emitting volatile acids.

A full description is given in: Jinping Zhang, David Thichett & Lorna Green (1994); and L.R. Lee. & D. Thickett (1996) (Bibliography).

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The Photographic Activity Test

In the world of museums and archives, photographic preservation is one of the areas that is actually quite well-defined in its distinction between "good" or "bad" storage materials. One test, The Photographic Activity Test (PAT), is standardized and described in the American National Standards Institute standard: ANSI/NAPM IT9.16-1993.

In short, the idea behind the test is to expose the material in question against two detector strips, one detecting image-interaction and one detecting staining. The detector strips are unprocessed colloidal silver emulsion on polyester film base, and fiber-base photographic paper, processed without development. The test specimen shall be cut into strips, which will be incubated against the surface of the detectors. Also a control test for each detector is done against pure filter paper. The test conditions are 70°C and 86% RH for 15 days. Before and after the test, the photographic density of the detector strips are measured, and the density changes caused by the test specimen are compared with the changes in the control test. According to the criteria described in the standard, the material then fails or passes the test.

The PAT is developed by the researchers at the Image Permanence Institute, located in Rochester at RIT.

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The Russel Effect

William Russel described around the beginning of the 20th century that freshly abraded metal plates could affect photographic plates, making a latent image suitable for developing. It was then shown that peroxides are formed on freshly abraded metal surfaces, this probably causing this "Russel Effect". Similarly, other peroxide-emitting materials will cause this, such as drying oils, wood, some paper types, etc.
    This test method is a quite elegant way to detect oxidizing vapors. Daniels (see below) has suggested using this method for testing materials that are intended for use with photographic materials. A modern photographic film must be specially sensitized so it will respond to even small amounts of peroxides. This can be done by ripening the emulsion with an ammonium hydroxide solution. The material to be tested should be kept in the dark for at least 3 days prior to testing, as exposure to light will cause photo-oxidation reactions on the surface of the material. For the actual test, the material should be kept in contact with the film emulsion for about 20 hours, after which time the film is developed as usual. Unsuitable materials for the enclosure of archival materials will form a dark image on the developed film.

This test is described in full by Daniels (1984) (Bibliography). It can, by the way, also be used to record paper watermarks.

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Passive sampling of carbonyls in situ

Many types of passive sampling devises (PSD) for a wide range of compounds in air exist. The advantage of passive samplers are that they are small, and therefore fits into confined spaces like a drawer or a show case. Also they are easy to use, and can be mailed from the sampling site to the laboratory for analysis. A sampling is quite compound-specific, so if one wants to screen for a number of compounds more samplers must be used.

A PSD can be a small tube, or a badge, which must be opened at the beginning of the sampling and right after placed at the sampling site. Sampling time will vary between hours and days, in general: the longer sampling time, the lower detection limit.

Advanced chromatography analysis methods are used for "reading" the result. Therefore its needed to deliver the PSD to an analytical laboratory after sampling. Analytical technique and detection limit are dependent on the type of PSD (the sampling media), the compound in question, the analytical method, and the sampling time.

Below is shown an example of a PSD for formaldehyde (GMD Systems Inc). For comparison of the size a Danish 20 KR coin is shown next to the badge:

GMD Formaldehyde Badge

References about passive sampling:

L.T. Gibson, B.G. Cooksey, D. Littlejohn & N.H. Tennent (1997): "Determination of Acetic and Formic Acid in the Museum Environment by Passive Sampling". European Cultural Heritage Newsletter on Research, vol. 10, June. European Commission - Environment and Climate Research Programme, Brussels, pp. 108-112.

L.T. Gibson, B.G. Cooksey, D. Littlejohn & N.H. Tennent (1997): "Determination of experimental diffusion coefficients of acetic acid and formic acid vapours in air using a passive sampler". Analytica Chimica Acta, vol. 341. Elsevier, The Netherlands, ISSN 0003-2670, pp. 1-10.

L.T. Gibson, B.G. Cooksey, D. Littlejohn & N.H. Tennent (1997): "A diffusion tube sampler for the determination of acetic acid and formic acid vapours in museum cabinets". Analytica Chimica Acta, vol. 341. Elsevier, The Netherlands, ISSN 0003-2670, pp. 11-19.

Cecily M. G. Druzik (1991): "Formaldehyde: Detection and Mitigation". WAAC Newsletter, Volume 13, Number 2, May. Western Association of Art Conservators, pp.13-16. Also avaible on the WWW: http://palimpsest.stanford.edu/waac/wn/wn13/wn13-2/wn13-208.html

Cecily M. Grzywacz & Dusan C. Stulik (1992): "Passive monitors for the detection of pollutans in museum environments". Pamela Hatchfield (ed.): AIC Objects Specialty Group, Postprints 1991, Vol. One. The American Institute for Conservation of Historic and Artistic Works, pp. 33-41.

Cecily M. Grzywacz (1993): "Using Passive Sampling Devices to Detect Pollutants in Museum Environments". Preprints of the 10th Triennial Meeting of the ICOM Committee for Conservation, Washington. International Council of Museums, pp. 610-615.

Barry Knight (1994): "Passive Monitoring for Museum Showcase Pollutants". Preventive Conservation: Practice, Theory and Research. Preprints of the Contributions to the Ottawa Congress, 12-16 September 1994. The International Institute for Conservation of Historic and Artistic Works (IIC), pp. 174-176.

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IAQ in Museums and Archives, December 11st, 2001


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