Ten samples of archeological copal from the medieval site Sharma
(Yemen) [38,39] have also been analyzed. They have already been
identified by separative techniques as eastern African and/or Mada-
gascar copals [34]. These raw fragments of copal have a same hard and
transparent bulk but different surface states and colors: from yellow
fragments with a thin dry surface, to orange fragments with a flaked-
off surface and finally red fragments with a thick and very friable
surface. This difference in the aspect might be related to different
surface conservation states. Adding this set of already studied copals is
a way to evaluate the representativity of the reference materials and to
assess the developed methodology on ancient samples. Moreover, the
different surface alteration states of these archeological fragments
should provide information about the impact of the materials degradation on their recognition and discrimination. For these archeological
copals, a specific sampling procedure was applied: the internal and
external parts of each fragment were separately analyzed to take into
account their heterogeneity.