New Analytical Technologies and Protocols
Conservation scientists are often called upon to test works of art and architecture with scientific equipment in order to answer a number of key questions:
- What materials did the artist use to make the object (characterization)?
- How did the artist make the object (technical art history)?
- When was the object made (dating)?
- Where was the object made (provenance)?
Answers to these questions help art historians, archaeologists, and conservators better understand the objects they are studying and preserving. In addition, research regarding how artists' materials change over time, and what we might do to slow deterioration processes, can help to preserve cultural heritage for future generations.
When no scientific instrument exists for performing the type of analysis that is requiredoccasionally to address profound, unanswered questions in conservation or art historyconservation scientists must design and build instruments that can provide more advanced, cutting edge scientific analyses. These new instruments may be the result of a technology transfer from other areas of scientific study, such as medicine or forensic science.
For instance, a new instrument was designed and built by the GCI for conservation research, which is based on an instrument used by NASA as part of the Mars Rover expedition. A portable X-ray diffractometer combined with an X-ray fluorescence spectrometer (XRD/XRF) was conceived to fill a gap in the quality of information obtainable solely by a traditional XRF instrument. By combining XRF with XRD, one can obtain elemental compositions, plus knowledge of how atoms are grouped together in molecules or crystals. This instrument has been quite useful for analyzing mineral pigments in wall paintings.
An example of an analytical instrument made specifically for art conservation is a microfadeometer. This device, developed by Paul Whitmore at the Art Conservation Research Center, Carnegie Mellon University, can measure the light sensitivity of an object. GCI researchers assembled a microfadeometer following Whitmore's specifications, and have used it to study how rapidly artists' colors fade when exposed to light and oxygen.
Considering that most laboratory equipment is manufactured for a wide range of industrial and research applications, conservation scientists commonly must adapt and modify these instruments before successful tests of works of art can be made. Industries that use equipment with potential conservation science application include environmental pollutant monitoring, drug testing, biomedical, plastics, petroleum, paints, and aerospace. Depending on the type of equipment, instrumental modifications can take various forms, such as making platforms for holding objects, development of software programs, or constructing sample chambers.
Essentially, all scientific instruments can be divided into two basic categories: non-invasive and invasive. Instruments in both categories have been successfully applied in the study of works of art, but have different strengths and weaknesses.
Non-invasive instruments can be used directly on works of art without touching them. For example, analytical imaging is a category of techniques that provides chemical composition or physical morphology that can be overlaid onto a map or photograph of the object. Multispectral imaging (MuSIS) makes point-by-point measurements of UV-Vis spectra over the surface of an object, and links the data to a map of the object. Another example is the laser speckle interferometer, a portable device developed at the GCI to record and decipher the pattern of laser light reflected off the surface of an artwork. This tool is capable of detecting holes and sub-surface defects beneath wall paintings and plasters, and has been used in wall paintings conservation projects. Polynomial texture mapping (PTM) was developed by Hewlett Packard Laboratories, and subsequently adapted at the GCI for portable use in documenting the fine texture of art objects. Portable PTM is especially well-suited for use on paintings, murals, and rock carvings because it can document surface changes caused by aging or conservation treatment. Finally, a computer tomography (CT) scanner was constructed at the GCI to record the interior details of small bronzes and sculptures, which helps provide information on how the objects were manufactured.
The vast majority of scientific instruments are invasive instruments that can only be used on samplesportions or bits of material that can be placed inside of the machine for measurement. Obviously, the process of removing samples from works of art is something that is done very carefully, with every effort made to minimize damage. Samples are often removed from unseen places on an artwork, such as beneath frames or decorative mounts, and also from beneath or behind an object. Some invasive instruments do not cause damage to a sample during the testing process, but instead leave the sample intact. These so-called non-destructive, invasive instruments are quite advantageous, because samples remain available for further testing using another type of instrument, thus increasing the amount of useful information that can be obtained from a single sample.
Proper protocols for handling and preparing samples for analysis are essential aspects of operating invasive analytical instrumentation. There is a desire to get the maximum possible information out of each test, because samples from works of art are precious and hard to come by. Thus, much time and effort can be required to develop adequate protocols for sample preparation, which, in large part, are based upon test results obtained for collections of artists' reference materials that match the composition of the object to be studied. An example of this work is the analysis of organic materials using gas chromatography/mass spectrometry (GC/MS). GC/MS was designed to study complex mixtures of organic substances, and has become a powerful analytical tool in petroleum analysis and environmental studies.
GCI scientists have worked to advance the state of the art in GC/MS analysis of natural and synthetic organic materials that have been used as paint media and varnishes. Their work incorporated innovative sample preparation procedures, extensive use of quantitative analysis, improved data interpretation techniques, and development of technical databases. Instructional workshops have been held at various institutions in order to widely disseminate their procedures. An example of the type of research in which GC/MS was applied is the Asian Organic Colorants project. Asian colorant source materials were collected, colorants extracted, pigments prepared, and a number of potential analytical protocols evaluated in order to optimize the analysis.
Current GCI Science projects in this area:
- Case Study: New Portable X-Ray Diffraction/X-Ray Fluorescence Instrument (XRD/XRF) (6pp., PDF, 568KB)
See also "New Technologies in the Service of Cultural Heritage" in the GCI newsletter vol. 25, no. 1.
Last updated: June 2010