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Laboratory Testing

Laboratory Testing.  Conducting scientific tests for desired information about coins and medals. While individuals can conduct specific gravity and ring tests without much equipment beyond balance scales, all other tests must be performed with scientific apparatus. There are two types: destructive tests (in which a specimen of material must be removed from the test piece and prepared for analysis), and the more desirable, nondestructive tests (which, in effect, removes only a imperceptible molecule or two of material). Nondestructive analysis include X-ray defraction, mass spectrography and neutron activation; chemical analysis is a destructive test.

Ideally the analysist would like to see inside the subject coin or medal and learn the composition throughout the piece, learn how it was formed (and, perhaps, the conditions of the forming). Without cutting into a specimen no one test is capable of revealing all this information, but each test provides evidence that, when combined with other data, leads the investigator to draw some conclusions.

These results include: the elements of metal forming the item, their quantity in the

area tested, the fineness of precious metals, and whether surface metals are different from those internally. Knowledge of these data can be so compelling that certain conclusions can be drawn for tested numismatic specimens. These include: authenticity of the specimen, fineness of its composition, and, somewhat, the source of the metal from which it was made. (Metal mined at each location has distinctive characteristics.)

Laboratory Testing Machines

Electron microprobe – high energy electrons are focused on a sample (about one

     micron size) and the reflected X-rays are analyzed by a spectrometer. One type

is called a Milliprobe.

Mass spectrograph – A high energy radiation is focused on a very thin layer sample, the time of penetration and amount of energy is measured to reveal the composition.

Microscopes – optical instruments for high magnification of minute objects; includes several kinds: stereo, comparative.  See MICROSCOPE.

Neutron activation reactor – measures gamma rays collected after a time when the sample is radiated with neutron rays (which induce radioactivity in

the atoms of the sample).


Vacuum X-ray quantometer – a type of spectrometer that measures refracted

     X-rays in a vacuum.

             Terms of Laboratory Testing              


 chemical analysis – qualitative analysis of a metal 

    sample to determine elements in its composition;  

    one method of separating the elements is by       



 density – the ratio of an object's weight to its    



 electron scanning – probing different spots on a    

    sample to reflect X-rays for measurement of       

    the reflected rays for analysis.                   


 gamma raysrays with a wavelength shorter than    

    X-rays which are emitted from nuclear trans-      



 isoprobe – probing the atom in a sample to learn    

    of the isotopes to identify the elements in the   



 mass absorption – the intensity of radiation        

    penetrating a layer of metal is measured; the     

    coefficient of this measurement identifies the    



 specific gravity – a ratio of the density (or       

    mass) of an object compared to that of water.     


 streak analysis – samples taken from a cleaned      

    edge of a coin are irradiated in a nuclear        

    reactor then analyzed for the elements present.   


 surface enrichment – the surface has a different    

    composition than the mass of the item; buried     

    coins often have such condition.                  


 tracer elements – minute particles of matter not    

    intended to be included in the composition.       


 spectrometry – measuring the index of refraction    

    of reflected rays.                                


 X-ray florescence – the analysis of the wavelengths  

    of polychromatic X-rays bounced off a metal sample;

    this reveals the elements at that point. This is a

    nondestructive technique.                         



B20 {1972} Hall and Metcalf.

N8  {1969} Clain-Stefanelli, "Technical Examination of Materials (Nondestructive Analysis)" pp 31-33.

N9  {1969} Laing, p 92-98.

N21 {1998} Hoskins.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


Roger W. Burdette, Editor

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