CORROSION OF METAL ANTIQUITIES — GETTENS 553 



quently than hitherto realized. It is also foimd on bronzes from 

 Anyang and other parts of central and eastern China. 



Paratacamite is the pulverulent green product of hydrolysis and 

 oxidation of synthetic cuprous chloride in moist air. It is also the 

 green powder that forms on chloride-corroded bronzes when the inner 

 unstable nantokite (cuprous chloride) layer is exposed to air by cross 

 sectioning or mechanical cleaning. It is not clearly stated in books 

 on mineralogy which of the dimorphs is more stable; but on basis 

 of museum experience it appears that paratacamite is the initial prod- 

 uct of rapid nantokite transformation, but that atacamite (perhaps 

 mixed with malachite) is the final one. The formation of parata- 

 camite is the manifestation of what is called "bronze disease," a 

 phenomenon which will be treated more fully mider "nantokite" {vide 

 infra) . 



Botallacite^ Cu2(OH)3Cl-H20, is another basic copper chloride. 

 It was found originally at the Botallack mine, St. Just, Cornwall, Eng- 

 land, and was first described by A. H. Church (1865). The 

 type specimen was placed in the British Museum (Natural History), 

 but for nearly a century no other occurrence of this mineral was re- 

 ported until a specimen of greenish-blue alteration product taken 

 from the interior of an Egyptian bronze figurine of the deity Bastet 

 in the Fogg Museum of Art was identified by Professor Clifford 

 Frondel of Harvard University as this same botallacite (1950). A 

 second occurrence on an artifact was observed by the author on 

 an Egyptian bronze censer in the Walters Art Gallery, Baltimore. 

 BotaUacite may occur on ancient bronzes more commonly than is 

 suspected. Dr. Frondel has described other natural basic copper 

 chlorides (1950) which someday may be found on an antiquity of 

 brass or bronze. 



Nantokite: Cross section studies on bronzes massively coated with 

 atacamite and on others coated with cuprite sometimes reveal an inner 

 layer of a pale gray waxy-looking substance which has been shown 

 to be cuprous cliloride, CuCl. It conforms to the unstable mineral 

 called iiantohite named from tlie first noted occurrence at Nantoko, 

 Copiapo, Chile. Because of its waxy appearance, Rosenberg (1917), 

 who seems to have been the first to describe its occurrence on ancient 

 bronzes, appropriately calls it "matiere stearineuse." Caley (1941) 

 found that nantokite v/as one of the principal alteration minerals of 

 the extensively corroded bronze and copper objects recovered from 

 deep wells at the site of the Athenian Agora, and from the Fountain 

 Peirene at Corinth. Various investigators have shown that nantokite 

 is the parent substance of both paratacamite and atacamite which are 

 described above and that it is the cause of "bronze disease." Gettens 

 (1932, 1936) described the occurrence of nantokite in corroded copper 

 nails from a second millennium B.C. Mesopotamian site called Nuzi 



