Testing Materials for Use in Exhibits
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Unknown or potentially hazardous construction and finish materials must be tested before they are used in an exhibition within close proximity to display objects.
Can some products be eliminated without going through the trouble of testing?[edit | edit source]
Reviewing as much information as possible about its chemical and physical properties is the first step in evaluating a potential construction material. This information includes the manufacturer's product information such as the material safety data sheet. Talking with the manufacturer's technical department and other museum personnel who have used the product can prove very useful.
Any of the following factors may affect the stability of the material or product:
- Stability of parent components and additives varies greatly. There are classes of unstable materials to be avoided. In particular, avoid urea formaldehyde, sulfur or "sulfonated" chlorine, ammonia, formic or acetic acid.
- Additives dispersed throughout the parent materials, including foaming agents, co-polymers, plasticizers, and bulking agents that affect the handling characteristics.
- Surface finishes affecting the handling or safety characteristics include slipping agents, permanent press finishes, moth-proofing, and fire retardents.
- Stabilizers added to increase the useful life of a product degraded by ultraviolet radiation, heat, visible light, or inherent chemical instability.
How do I test materials selected through initial research?[edit | edit source]
A number of simple methods can be used to test a sample of the material. None are as scientific as chemical analysis using mass spectroscopy or other appropriate equipment. While the techniques listed below can be used as an indicator, results may not be entirely accurate or repeatable.
- Enclose the sample in a clean, dry glass vial with an all-glass or all-metal lid. Set the jar in the sun or another heated location. If a smell is noticeable when opening the jar after several days it is likely that chemicals have outgassed from the material.
- A plastic material can be tested for the presence of chloride by placing a sample on the end of a copper wire and heating it in the flame of a gas burner. A green flame indicates chloride.
- The "Oddy" test identifies materials that are particularly inappropriate for use due to high amounts of outgassing. A material that passes the Oddy test may not, however, be stable over the long-term. Many products include stabilizers which may not be exhausted during the course of this test.
How is the Oddy test procedure carried out?[edit | edit source]
The following "Oddy" test method is based on enclosing a sample of the material to be tested in a well-sealed container along with polished blanks of metal and a piece of pH-neutral paper. A moisture reservoir in the container maintains a high humidity and the container is heated; the heat and moisture accelerate reactions. The test blanks are visually inspected daily and any changes in appearance recorded. A determination of material suitability is made based on the speed and severity of any reaction.
The test requires two containers; glass containers sealed with PTFE tape or glass jars with all-metal screw lids can be used.
- Control container: Required for a comparison and to insure that a problem with the test preparation itself does not cause a false reaction. The control contains metal blanks of silver, copper and lead and pH-neutral paper, but not the material to be tested.
- Test container: Includes as much sample of the material to be tested as possible. Metal blanks of silver, copper and lead and pH-neutral paper are used as indicators of harmful volatile chemicals. Record the initial pH of the paper. Allow one half of each test blank to overlap the material being tested. This will test for problems caused by contact with the material as well as deterioration caused by chemical outgassing.
Place a small vial of water in each container and seal. Place both containers in an oven at approximately 140°F (60°C). Avoid opening the containers during the test period as this will dissipate any outgassing. Examine the blanks daily for signs of corrosion, pitting, tarnishing, or other change; record and date observations. The pH of the paper is measured at the end of the test.
The test should be run for a four weeks. The method is best at screening out particularly unstable products. Additives that improve the aging characteristics of a material may not be exhausted during the test. Also, low levels of emissions over longer periods of time may cause damage not detected during the relatively short testing period.
Products, Manufacturers, and Suppliers[edit | edit source]
Mention of a product, manufacturer, or supplier by name in this publication is for information only and does not constitute an endorsement of that product or supplier by the National Park Service. Listed materials have been used successfully in past applications. It is suggested that readers also seek alternate product and vendor information to assess the full range of available supplies and equipment.
- Silver- 99% foil l l/2" x 0.004" 5X0l65 030 GM
- Copper- foil 0.005" thick C11549-100GM
- Lead- foil 12" x 0.008" thick L27-l1B
Polishing Materials and Glassware
- Precipitated carbonate
- Denatured Ethyl Alcohol
- Flasks/Petri Dishes