CORROSION OF METAL ANTIQUITIES — GETTENS 549 



immediately after recovery of the artifacts from soil or sea or after 

 long storage to ready them for exhibition and display. Herein lie 

 certain dangers and opportunities for oversight, not only because of 

 possible damage to the object itself from enthusiastic but untrained 

 hands, but because of inadvertent loss of valuable historical and scien- 

 tific information which may be contained in or concealed under 

 unwanted encrusting materials. In the mineral shell there may be 

 evidence of metal composition, of age, and even of place of origin. 

 The corrosion crust sometimes has a layered structure containing two 

 or more distinct minerals in which the outer more stable minerals 

 can serve as natural protective coatings for less stable compounds 

 lying beneath. For these several reasons corrosion crusts should be 

 carefully examined and identified by an expert before they are scraped 

 away or dissolved off by a technician and thrown casually into waste 

 jar or sink. An added reason for the careful examination of corro- 

 sion crusts is that they may contain rare minerals imknown or little 

 known to science which add greatly to their interest and importance. 



In industry the utilitarian terms "corrosion" and "corrosion 

 products" are widely used to describe the chemical and electrochemical 

 changes in which the metal passes from the elemental to the combined 

 state, and those terms, for practical purposes, are retained here al- 

 though some mineralogists seem to prefer the terms "mineral altera- 

 tion products" and collectors still prefer to speak of any kind of altera- 

 tion of the surface as patina. In the various modern textbooks on 

 corrosion of metals the emphasis is almost entirely on causes of corro- 

 sion, corrosion mechanism, and corrosion prevention, but hardly any 

 consideration is given to the products of corrosion. These appear to 

 be unwanted materials that are scraped or brushed away or covered 

 over. 



In the early part of this century the microscopic identification of 

 mineral alteration products using methods of optical crystallography 

 was slow and laborious. The task was made difficult by the finely 

 crystalline character of the alteration products and complexity of 

 the mixtures. Today, using X-ray diffraction and X-ray fluorescence 

 methods of analysis, identification of inorganic crystalline materials is 

 much easier, and what was formerly wearisome and time consuming 

 has become fast and routine. 



This paper gathers together, classifies, and briefly describes the 

 wide variety of mineral corrosion products that occur on ancient 

 metal objects. It is an exercise in taxonomy within the widest mean- 

 ing of that term. Precise criteria for recognizing mineral species 

 will not be given because those are adequately dealt with in standard 

 texts on mineralogy. No attempt will be made here to explain cor- 

 rosion mechanism or corrosion theory. That has been treated by 



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