Preserving museum pieces through analytical chemistry

Preserving museum pieces through analytical chemistry

Those responsible for authenticating, preserving or restoring museum pieces often turn to analytical chemists for help in their efforts to save history. Restoration experts, for example, need to know the chemical identities of the pigments, binding media and other materials that past artists used originally. Museum conservators need similar information for making decisions about what solvents or finishes to use for preserving a particular piece (SN: 4/23/88, p. 264).

Restorers at the J. Paul Getty Museum in Malibu, Calif., for instance, wanted to know the identity of the binding medium (a substance that holds pigments to a surface) in the paint that Bartolommeo Montagna used in his 1495 painting "The Adoration of the Magi." With researchers from the Getty Conservation Institute in Marina del Ray, Calif., chemist James M. Landry of Loyola Marymount University in Los Angeles and Margaret R. Bolton, one of his undergraduate students, analyzed a tiny sample of the painting using an instrument called an infrared (IR) microspectrometer.

The researchers embedded the sample in a plastic and then sliced it into slivers thinner than a human hair. The spectrometer shines infrared light through each sliver and monitors which wavelengths get absorbed. The resulting pattern, called an IR Spectrum, identifies the chemical constituents of each slice, and thus of the painting at different depths. To help them make accurate identifications, Landry and Bolton obtained reference spectra from samples of art materials in common use at the time Montagna painted.

Landry now seeks an embedding material transparent enough for viewing of a sample through an optical microscope, yet also suited for doing chemical analyses on the same sample. To make this possible, the embedding material must have a composition that does not distort a sample's IR spectra. Getting as much information out of as little a sample as possible is a premium concern for art restorers and conservators, Landry says.