2015-08

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Corrosion Testing is routinely applied in conservation and preservation laboratories, because many materials used in storage and exhibitions emit volatile components that can corrode metal artifacts, especially lead, copper, and silver. This corrosion not only damages artifacts, but can also lead to loss of historical information (such as nuances of surface details, designs, deliberate patinas, and inscriptions). Most museums rely on a simple exposure test with visual assessment, dating back to the 1970s and similar to what was used in industry at the time, called the “Oddy test.” Over the years many publications have highlighted problems with accuracy, reproducibility, subjectivity, and the length of time required (30 days) for this type of test. Professional corrosion studies and industry scientists now use alternative methods that are faster and more quantitative. however the Oddy test remains firmly entranced in conservation practice, mainly because it is simple to carry out, needs only inexpensive and easily-available equipment and supplies, and requires no corrosion science expertise. Yet, the required four-week period is often cited as a problem, because exhibition designers and suppliers frequently need to know much more quickly than that if purchases should go forward; thus the test is often abbreviated to two weeks, decreasing reliability.

The rapid corrosion test described in this project appears to be successful in screening for materials that are likely to be very damaging if used in conjunction with a particular metal. This information is available in a 24-hour period for lead and copper, and within four days for silver. Materials that pass this screening test could be selected for follow-up testing via other means that require more time or expensive equipment, while the materials that are clearly damaging to metals can be eliminated from consideration very quickly. The rapid test also appears to be a period was successful in showing which corrosion inhibitors work well to protect metal. This test would allow for the rapid screening of many possible inhibitors, in a variety of concentrations, and with replication. The solutions producing the best results could then be set aside for more detailed study and experimentation by a variety of other means.

The research conducted during this project also indicates that both the rapid tests and the traditional Oddy tests can be improved by incorporating Reflectance Transformation Imaging (RTI) for corrosion assessment and permanent documentation of results. RTI is commonly employed in museums and conservation laboratories, is very fast to accomplish, and this step can easily be added. An RTI image can be viewed at many different light positions and enhancement conditions, to provide the best possible view of the rapid corrosion test plate or an Oddy test coupon array. Adding in image analysis is also a very fast step. The enhancement capabilities of image analysis software can aid qualitative judgements, and quantitative data can also be obtained if desired.

National Center for Preservation Technology and Training
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Email: ncptt[at]nps.gov
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