CORROSION OF METAL ANTIQUITIES — GETTENS 555 



green removed from a weather-exposed bronze lamp post in front of 

 the Freer Gallery of Art in Washington, D.C., gives a brochantite 

 pattern. Kosting (1937) also fomid that the green on a 10-year-ex- 

 posed copper roof in Washington, D.C., is brochantite over a layer of 

 cuprite. He further notes that only antlerite vras detected in the 

 patma from copper that was formed by accelerated weathering in the 

 laboratory. There is good evidence that the green on copper roofs 

 and statutary bronze in urban areas is mostly basic copper sulfate, 

 formed from sulfur compounds produced in the burning of coal and 

 fuel oil. Vernon and Whitby (1930) in the late 1920's carried out 

 extensive researches on the green of copper roofs in London and other 

 parts of England. They concluded that the main constituent of the 

 green alteration product is basic copper sulfate and that it corresponds 

 to the mineral brochantite when it has been exposed long enough to 

 attain full basicity (cupric hydroxide content). This may require 

 upward of TO years. Mixed with basic copper sulfate are lesser 

 amounts of basic copper carbonate and of copper chloride whose com- 

 positions correspond to the minerals malachite and atacamite when 

 they reach full basicity. 



Connellite: Eecently H. Otto (1963) reported on the basis of X-ray 

 diffraction analysis the occurrence of the rare mineral connellite^ 

 [Cui9(S04)Cl4(OH)32-3H20?], on rings made of bronze sheets from 

 the only group of graves of the La Tene Period f omid in southwestern 

 Germany. The bright blue needlelike crystals of connellite occur 

 mixed with other copper minerals in the bronze corrosion crusts. 



COPPER SULFIDES 



Sulfides are not often reported as occurring on copper artifacts, 

 but they might be expected where objects have been in contact with 

 sulfur-bearing waters. Both Austin F. Rogers (1903) and F. W. 

 Clarke (1924) mention the investigations of A. G. Daubree (1875, 

 1881) and others who examined Roman coins and medals recovered 

 years ago from French mineral springs and report occurrences of chal- 

 cocite, CuaS, chalcopyrite. CuFeSa, homife, Cu5FeS4, and tetrahedrite, 

 (Cu,Fe)i2Sb4Si3. Daubree (1875) also noted the occurrence of indigo 

 blue covelUte, CuS, among the other sulfide minerals in the corrosion 

 crusts of coins. He believed the sulfide in the thermal spring water 

 came from the reduction of soluble sulfates by bacterial action on 

 vegetable material. Quite recently Mendel Peterson of the Smith- 

 sonian Institution recovered several fragments of a much corroded 

 copper gunpowder can from the wreck of the VHerminie^ wooden flag- 

 ship of the French West Indies flieet, sunk off Bermuda in 1838. Ex- 

 amination showed that the copper metal was completely altered to 

 a blue-black brittle mass, identified by X-ray diffraction analysis as 



