CORROSION OF METAL ANTIQUITIES — GETTENS 565 



ZINC 



Although the Romans, and later the Chmese, produced brass or 

 copper-zinc alloy, and zinc metal probably came into use in China 

 and India in the Middle Ages, it was not recognized in Europe as 

 a distinct element until the 18th century. After that zinc gradually 

 came into commercial production in the West. Because of its early 

 scarcity and also because of the chemical activity of zinc, few objects 

 of that metal have survived from antiquity, hence little attention 

 has been given to its alteration products. A grayish crust on a 

 19th century Italian ink pot of zinc, now in the United States 

 National Museum, was shown to be hydrozincite^ Zng (OH) 6(003)2. 

 A single occurrence of rosasite [(Cu, Zn) 0(011)2003], similar in out- 

 ward form to botryoidal malachite, but bluer in tone, was identified 

 at the Department of Mineralogy, British Museum (Natural History)^ 

 on a Chinese bronze cannister of the Han period, and also on a Chinese 

 vessel of the type tui of about 300 B.C. Smithsonite, ZnCOa, and 

 perhaps some other rare copper-zinc minerals may appear someday. 



CONCLUSION 



The accumulated knowledge of mineral alteration products on metal 

 antiquities has practical as well as academic interest. The collector 

 and curator of metal antiquities can use the information to supple- 

 ment stylistic, historical, and epigraphic evidence in judging age, au- 

 thenticity, and condition of newly met objects. Although it is rarely 

 possible to estimate age and authenticity or antiquities solely on the 

 kind and extent of mineral alteration products, these materials can 

 provide valuable background information. They permit detailed 

 and close comparison of objects of unknown provenience with those 

 whose age and source are known. The pale green tin oxide water 

 patina on a Chinese bronze ceremonial vessel of Shang Period is unique 

 and characteristic of its time and place of origin. The dark green 

 crj'stalline crusts of atacamite on an Eg}"ptian bronze figurine may 

 not assure ancient Egyptian origin; but if other attributes indicate 

 the source as Egypt, the presence of mineral chlorides lend support- 

 ing evidence. Knowledge of the kind and character of corrosion 

 products is essential to a rational method of cleaning metal objects. 

 To increase the background knowledge necessary for the understand- 

 ing and the conservation of metal antiquities, archeologists and col- 

 lectors must begin to look upon decay and rust with a more appre- 

 ciative and sympathetic eye. 



• Private communication, R. M. Organ. 



