The Corrosion Products of Metal 

 Antiquities' 



By Rutherford J. Gettens 



Head Curator, Freer Gallery Laboratory, Freer Gallery of Art 

 Smithsonian Institution 



[With 10 plates] 



Archeologists who find the remains of metal antiquities in the earth 

 or in the sea have observed the wide variety of products that encrust 

 their surfaces. These encrustments are caused by the chemical inter- 

 action of the metal with the corroding agencies of earth, air, and water. 

 Many generations of museum curators and collectors have been con- 

 cerned with the nature of these products, especially when they want 

 to show a corroded object close to its original condition. A few chem- 

 ists have investigated metal corrosion crusts, and have been impressed 

 by their diversity and complexity. Mineralogists have observed in the 

 corrosion crusts crystalline compomids identical with some of the 

 minerals of the earth's crust. Information about these inorganic 

 mineral products in corrosion crusts is scattered far and wide in the 

 scientific literature and in unpublished notes in museum files and 

 laboratory notebooks. It is important that it be collected, classified, 

 and made readily available to the collector, curator, and the scientific 

 investigator. 



The term "mineral" is used to designate the chemical elements or 

 compounds occurring in the earth's crust as a product of natural 

 inorganic processes. Minerals have more or less constant chemical 

 composition and characteristic atomic structure, and hence character- 

 istic crystallme form and physical properties. Most minerals can have 

 chemical formulas assigned to them. Metal corrosion products give 

 X-ray diffraction patterns identical with their mineral prototypes, 

 thus the same chemical formula can be assigned with confidence to the 



' A prelimiuary report under the title "Mineral Alteration Products of Ancient Metal 

 Antiquities" was read at the First Conference of the International Institute for Con- 

 servation of Historic and Artistic Works (IIC) in Rome, 1961. This report has since been 

 published In the collected papers of the Rome Conference under the title "Recent Advances 

 In Conservation." London: Buterworth and Company (1963), pp. 89-92; edited by G. 

 Thomson. 



547 



