4 COMPARISON OF THE IODIDE-IODATE AND CHROMOTROPIC ACID TESTS WITH THE ODDY TEST

4.1 THE ODDY TEST

The Oddy test is used routinely in many museums, including the British Museum (Oddy 1973). In this test, a sample of material is enclosed with a coupon of cleaned metal. Corrosion is accelerated by adding water to create high humidity and by elevating temperatures (60�C). After 28 days, the extent of corrosion on the metal coupon is used to evaluate the suitability of the material under test for use in the display or storage of artifacts containing that metal.

A range of materials commonly used for storage or display of antiquities was tested using the iodide-iodate test, the chromotropic acid test, and the Oddy test with lead. Lead is highly susceptible to the corrosive effects of both volatile organic acids and formaldehyde.

Four of these materials were chosen to be tested for free formaldehyde using a quantitative aqueous extraction method, modified BS6806, part 2 (British Standards Institution 1987). This method also uses chromotropic acid, but the intensity of the color of the solution is measured using an ultraviolet/visible spectrophotometer.

4.2 DISCUSSION

There were no instances in which the results of both the chromotropic acid and iodide-iodate tests failed to identify a material that had caused corrosion of lead in the Oddy test and hence was classified as unsuitable for use with lead. In two instances (BM reference numbers 2065 and 2532), the evolution of formaldehyde was detected by the chromotropic acid test, but no corrosion was seen on the lead from the Oddy test. Using the aqueous extraction method, the material BM reference number 2065 contained 336 mg/kg of free formaldehyde. This material produced a purple color in the chromotropic acid test (i.e., gave a positive test result), but it did not cause corrosion of lead in the Oddy test. On testing the material BM reference number 2517, 1177 mg/kg of free formaldehyde were detected. This material did cause the lead coupon in the Oddy test to corrode.

These results suggest that the chromotropic acid test will detect levels of formaldehyde that are too low to cause corrosion.