Linking the Past and the Future: Understanding How Pollutants Cause Corrosion During an Oddy Test

Artifacts and artwork continue to tell a story long after a time or culture has disappeared. Preventive art conservation science involves careful and responsible management of the objects entrusted in the care of the museum staff to ensure environmental and display conditions do not cause damage so future generations can observe and learn about past cultures. An accelerated metal corrosion test, the Oddy test, has been used to help determine the suitability of display and storage materials. The Oddy test is subjective, so newer methods are being developed involving the use of gas chromatography and mass spectrometry to identify specific pollutant molecules emitted from a sample. It can be challenging to link these two methods as they may generate differing results. The Oddy test may indicate the lead coupon was corroded by organic acids, but multiple organic acids may be detected during GC analysis. The focus of this work is to determine which types of acids act as pollutants. Volatile acids are known to corrode the lead coupon through direct oxidation of the metal by the acid at the surface of the metal coupon, but the impact of nonvolatile acids on the lead coupon is still inconclusive. Preliminary results confirm the mechanism of corrosion by volatile acids. In addition, a different pathway has been found for corrosion of lead catalyzed by the presence of a nonvolatile organic acid pollutant. Experiments to elucidate the mechanism for acid corrosion of lead in the Oddy test will be shared.