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 Harbor and from roofs at AT&T Bell Laboratories in Murray Hill, N.J. ranged in atmospheric exposure from 1 year to 100 years. X-ray diffraction showed the presence of cuprite (Cu sub 2 O) and brochantite (Cu sub 4 (SO sub 4) (OH)sub 6) in all specimens and antlerite (Cu sub 3 (SO sub 4) (OH) sub 4, up to 0.7 times brochantite), atacamite (Cu sub 2 Cl (OH) sub 3, up to 1.6 times brochantite), and/ or posnjakite (Cu sub 4 (SO sub 4) (OH) sub 6 H sub 2 O), up to 5.2 times brochantite) in some. Posnjakite has been previously reported as a patina component only once, following 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 (evolved gas analysis) gives additional information concerning patina composition, in particular to the presence of both carbonate and oxalate in widely varying ratios, and of several different chlorine- containing species.