I don't see any information about how the icon was tested for age. There was an exhibit of Ethiopian Icons at the Smithsonian about 5 years ago.
Here is some info about testing etc from the time of that exhibit.
Technical Study of Ethiopian Icons, National Museum of African Art ...
This article describes a technical study of six Ethiopian icons at the National
Museum of African Art, Smithsonian Institution, and includes a brief synopsis of
the history of Ethiopian painting. The preliminary research involved visual and
photographic examination using ultraviolet fluorescence and infrared color
photography as well as x-ray radiography. Following this initial examination,
dispersed pigment samples and cross sections were analyzed using polarized light
microscopy. In addition, the cross sections and loose samples were analyzed
using scanning electron microscopy with energy dispersive spectroscopy
capabilities, x-ray fluorescence, Fourier transform infrared spectroscopy, and
x-ray diffraction. The technical study clarified the techniques and materials of
Ethiopian icons. The paint layers contained the following pigments: cinnabar,
orpiment, indigo, smalt, Prussian blue, terre verte, gypsum, charcoal black, and
earth brown. In addition, gypsum was identified as the main component in the
ground layer. The binding medium in the pigment and ground was characterized as
proteinaceous. This technical study provides insight into icon production in
Ethiopia from the 17th to 19th centuries.
Journal of the American Institute for Conservation © 2005 The American Institute
for Conservation of Historic & Artistic Works
Exhibit at the Smithsonian:http://www.nmafa.si.edu/exhibits/icons/index.html
Some more pictures of icons by Betsy Porter:http://www.betsyporter.com/Ethiopia.html