An exposure test of procelain enamels at seven representative sites in the continental United States was initiated by the National Bureau of Standards and the Porcelain Enamel Institute in 1956. After seven years all specimens were returned to the Bureau and the changes in gloss and color determined. These changes were found to be different al all exposure sites except Pittsburgh and New Orleans. The most severe changes occurred for specimens exposed at Kure Beach, 80 fee from the ocean, while the least change occurred for specimens exposed at Los Angeles. The differences in behavior of the specimens correlated with both the relative humidity and the pH of the suspended particulate matter at the different sites. A direct relation existed between the acid resistance of the enamels and weather resistance. However, enamels of different types, such as enamels on aluminum and steel, having the same acid resistance did not necessarily show the same weather resistance. Comparison with enamel specimens exposed for seven years in an earlier test showed that porcelain enamels produced after the end of World War II were equally resistant to changes in gloss at the Washington, D. C., site as those produced before the war. As a group, the regular glossy acid-resistant enamels on steel showed the best weather resistance of the various types tested. No corrosion of the base metal was noted for any specimen on which the initial coverage was complete. (Author).

An exposure test of porcelain enamels on aluminum was initiated by the National Bureau of Standards and the Porcelain Enamel Institute in 1964.The enamels were returned from the exposure sites to the laboratory at NBS to be measured for changes in gloss and col * or after exposures of six months, one year, and three years.Changes were found to be greatest at Kure Beach and least at Montreal and Los Angeles, with moderate changes occurring at Washington and New York.Although the boiling citric acid test is used as an acceptance test for these enamels, the correlation with color change, particularly at Kure Beach, was not as good as expected.A cupric chloride test was developed which shows an improvement in this correlation.(Author).