Analytical Techniques: Microscopy

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The information presented on the Paintings Conservation Wiki is the opinion of the contributors and does not imply endorsement or approval, or recommendation of any treatments, methods, or techniques described.

Author: Jessica Ford

Editors: Anne Schaffer, Kari Rayner

Microscopy

Optical microscopy is the study of works of art under magnification, either in-situ or focused on a small sample (Eastaugh and Walsh 2012). Microscopic examination of an in situ painted surface by a trained conservator can yield an extraordinary amount of information about artistic technique, condition, and material content. Stereomicroscopes are used most commonly, sometimes in tandem with ultraviolet illumination and/or a camera. Some high magnification and multifunctional microscopes, such as a Hirox microscope, are able to graphically render the 3-dimensional topography of a surface and non-invasively examine stratigraphy by zooming into the depth of cracks. Compound microscopes allow for the examination of small samples taken from paintings using higher magnification.

Polarized Light Microscopy

Polarized light microscopy (PLM) is the examination of visual and morphological properties of dispersed pigment, canvas fiber, paper fiber, or wood panel samples to gain qualitative information. This technique requires destructive sampling from the painting, but depending on how the sample is mounted, it may be reused for further analysis. Microchemical testing can be employed to help identify the material in question; however, staining may limit the sample’s potential for reuse.

Cross-Section Microscopy

Cross-section microscopy is the examination of the stratigraphy of a painting to yield qualitative information about artistic technique, condition, and material content that cannot be ascertained by viewing the surface of a painting alone. A microscopic sample that includes the full stratigraphy of a painting, from topmost surface to ground layer or substrate, is removed, embedded in resin, and polished along its depth for clear viewing of the stratigraphy. Microchemical staining can be performed on a cross-section to characterize and locate oil, gum, or protein in binding media throughout a painting’s stratigraphy, which can be instructive for both contextualizing a painting stylistically, historically, and/or culturally; and deciding on an appropriate treatment (Wolbers et al. 2012). After staining, it may not be possible to reuse the sample for other types of analysis.

References

Eastaugh, N., and V. Walsh. 2012. Optical microscopy. In Conservation of easel paintings, edited by J. H. Stoner and R. Rushfield, 306–17. Abingdon, Oxon England: Routledge.

Wolbers, R. C., S. L. Buck, and P. Olley. 2012. Cross-section microscopy analysis and fluorescent staining. In Conservation of Easel Paintings, edited by J. H. Stoner and R. Rushfield, 326–35.. Abingdon, Oxon England: Routledge.