The characterization of patina components by X-ray diffraction and evolved gas analysis

Fourteen patinated copper specimens, seven each from the Statue of Liberty, New York Habor and from roofs at AT&T Bell Laboratories in Murray Hill, NJ, ranged in atmospheric exposure from 1 to 100 years. X-ray diffraction showed the presence of cuprite, Cu 2O, and brochantite, Cu 4(SO 4)(OH) 6, in all specimens and antlerite, Cu 3(SO 4)(OH) 4 (up to 0.7 times brochantite), atacamite, Cu 2Cl(OH) 3 (up to 1.6 times brochantite), and/or posnjakite, Cu 4(SO 4)(OH) 6 · 2H 2O (up to 5.2 times brochantite) in some. Posnjakite has been previously reported as a patina component only once during short term exposures in Eurasia. It appears to be an early corrosion product which subsequently converts to brochantite. Mass spectrographic examination of gases emitted from heated patinas provides further information on patina composition, in particular on the presence of both carbonate and oxalate in widely varying ratios.