Chemistry Reference
In-Depth Information
marble that are from different sources or that have undergone different
weathering processes, for example, even though appearing similar in day-
light, emit different fluorescence. Thus, areas of contrasting fluorescence
observed on the surface of marble sculptures illuminated by ultraviolet light
may reveal that parts of the marble were either replaced during restoration
or faked. Also, differences between the fluorescence of genuine and manip-
ulated patina on bronze objects, and of different pigments of the same color
on painted surfaces, provide clues for differentiating between them and
identifying their nature.
Radiography.
Penetrating radiation
is absorbed to varying degrees by dif-
ferent materials, and this property makes them useful for examining (
radi-
ographing
) solid objects (see Textbox 11). The shape of wrapped or encased
objects, as well as the internal structure and condition of solid objects, can
usually be revealed using conventional X-rays radiography. Extremely large
objects, or objects to which X-rays equipment is not accessible, can be
radiographed using the
gamma-rays radiography
technique, while
neutron
radiography
is useful for revealing the structure of objects made of organic
materials. The information provided by radiographs could otherwise be
obtained only by damaging the specimens examined. Consequently, radi-
ographs are of much help for establishing the internal structure of ancient
objects, authenticating questionable ones, and detecting forgeries. Thus have
been radiographed a wide variety of archaeological objects and structures,
including metal casts and mummies. The X-rays radiography of a small
mummy found in the tomb of an Egyptian high priestess from the twenty-
first dynasty, for example - which until radiographed was believed to be that
of her daughter - revealed that it was actually of a baboon.
Occasionally, because of the large dimensions of some objects and/or
the high density of the material from which they are made, X-rays may not
be of sufficient energy to penetrate them, and their radiographs may provide
no useful information. In such cases the gamma rays of highly energetic
radioactive isotopes provide penetrating radiation of sufficient energy to
reveal hidden details and/or unexpected material components.
Chemical Analysis.
The chemical composition of ancient objects is impor-
tant for their authentication. The nature as well as the relative amounts of
major, minor, and trace elements in any object are of use for determining the
authenticity or otherwise of ceramics, glass, or alloys. A wide range of
analytical techniques, depending on the nature of the material studied, have
been used for this purpose, including X-rays fluorescence analysis, mass
spectrometry, atomic absorption spectroscopy, and neutron activation analy-
