The Application of Chemistry to the Examination of Works of Art

Suzanne Quillen Lomax
National Gallery 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 collection of the National Gallery of Art.