"THE APPLICATION OF CHEMISTRY TO THE EXAMINATION OF WORKS OF ART"
Scientists have been associated with museum conservation
laboratories for many years. Only recently, however, have art curators
and conservators begun to appreciate the contributions that scientists
can make in the preservation and restoration of art objects. At present,
about a dozen museums in the United States have conservation science departments.
Art conservators frequently require specific information
about the component materials of a painting or object prior to treatment.
Due to their complex stratification, most questions that arise concern
the nature of the components of paintings. Microscopic cross sections
of a painting are frequently taken and viewed with a polarizing microscope
to understand the different layers that make up the object. Pigment
identification is frequently employed to determine if the pigments are
in keeping with the time period of the object, as well as to understand
the artists’ materials and methods. They are performed using polarized
light microscopy and x-ray diffraction of powdered samples, or x-ray fluorescence,
which is well suited to this task due to its non-invasive nature.
To study the identity of binding media, the conservation
scientist uses gas chromatography (GC), high-performance liquid chromatography
(HPLC), and infrared spectroscopy. GC is used to identify oil-containing
binders, as well as for the identification of waxes and various low molecular
weight resins. HPLC can be used to identify proteinaceous binders
and organic dyes. Ultraviolet radiation can be used to examine the
varnish layer of a painting as well as to identify areas retouched in previous
conservation treatments. Infrared reflectography is frequently used
to examine underdrawing on a painting. In addition, x-rays are often
used to determine where lead white has been used on a painting, as well
as to reveal damaged areas beneath the painting’s surface.
The talk will focus on the application of these various
techniques to the examination of paintings and sculpture. Examples
will be presented from the National Gallery of Art collection.