IMR: Development of a Confocal X-ray Fluorescence Microscope for Three-dimensional Composition Analysis and Student Training

Cornell University, Ithaca NY

Investigators

Abstract

This award from the Instrumentation for Materials Research Program supports Cornell University to develop a fast scanning, confocal, x-ray fluorescence (XRF) microscope for three-dimensional composition mapping of complex solid-state materials. The microscope consists of two x-ray optics arranged as shown at the right: one optic focuses the incident beam onto the sample, and a second optic collects x-ray fluorescence. The overlap of the two focal regions is several tens of microns in extent, and defines the active, or confocal volume of the microscope. Feasibility work over the past year at CHESS has demonstrated that a depth resolution of several microns can be achieved. This microscope will meet a pressing demand in art conservation to nondestructively determine the composition of paint layers as a function of depth in historic oil paintings. This project represents a fruitful, interdisciplinary collaboration between scientists and students from Cornell University, the University of Delaware, and the Winterthur Museum, and will result in knowledge and tools having both general interest and broad application. This knowledge will be disseminated via journals and conferences in each of these fields of study, and via the Winterthur museum itself. Throughout history, painters have reused old canvases, painting over their own work or the work of earlier artists. This practice has led to the presence of unseen works by old masters such as Rembrandt, Tintoretto and Van Dyck. For this and a variety of other reasons, art conservators, museum scientists, and art historians wish to obtain information about paint layers below the presentation surface of a painting. Scientists working in collaboration with conservators and curators have devised a number of tools for the inspection of paintings. Most of those tools, however, only look at the surface of the opaque paint. What they miss is a view of the buried layers of paint beneath (and all of the art historical information that these layers contain). A new tool called an "x-ray confocal microscope" will give art historians the unprecedented ability to study multiple, buried layers beneath a painting surface without harming the painting in any way. Developed by scientists at Cornell University, University of Delaware and the Winterthur Museum, this advanced microscope uses depth-sensitive x-ray measurements to probe beneath the surfaces of paintings and produce detailed maps of paint layers with precise chemical sensitivity. The microscope works by focusing a small x-ray beam (approximately 20 micrometer in size) into the painting and collecting the resulting fluorescent scattered x-rays from only a specific depth. The x-ray signal from the buried paint layers can be analyzed to identify which specific atoms are present in the paint. The x-ray measurements can be done without touching or harming the original painting in any way, a matter of great concern to the art conservators and curators charged with the care of these beautiful and irreplaceable works.