The metallography is a method of expertise which aims at authenticating a metallic object. This test consists in cutting off a sample from the objects to authenticate, in polishing the metallic fragment after its coating with resin and in observing, with the help of a microscope equipped with an inverted lens, the structure and the composition of the alloy as well as the aspect and the possible deep penetration of the corrosion products.
Objects made out of copper alloys (cf. bronze, brass) or even auriferous alloys (cf. “tumbaga”)
This type of examination allows to reveal :
- The inner corrosion in old bronzes from which the external patina has been completely removed ;
- The false patinas obtained from paint or corrosion products taken from ancient objects;
- The external patinas or internal deteriorations resulting from an accelerated corrosion induced by immersion in acid solutions;
- To identify the method used for the assembling of parts which have been cast separately (cf. hard solder, tin-lead solder);
- To give precise details about the manufacture mode of metallic objects (cf. hammering).
Metallography of an authentic object : illustration of the phenomenon of superficial stannification (tin enrichment of the surface due to the elimination of the copper corrosion products)
Metallography of a modern object : homogeneous structure, fake superficial corrosion products and lack of any intern corrosion
