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Infrared Reflectography

Comparison of Infrared and Visible

Infrared Reflectography reveals underdrawing (as seen in the first image) that was not seen in the visible light (right image). [Right Image by Don Hurlbert, CSIP, Smithsonian Museum of Natural History]

Infrared Reflectography is a non-destructive technique used by conservators to examine paintings and artworks and detect hidden details under the upper layers such as added paint, underdrawings, and hidden signatures or watermarks. The technique has been used to discover details of artists’ creative processes, alterations and reworking. The infrared examination also can be used as a tool to differentiate between certain groups of pigments and inks.

Infrared Reflectography is the recording of the variable absorption and reflectance of infrared light by an object. The infrared wavelengths may penetrate an object below the surface, unlike visible light. In the case of paint or paper with charcoal or carbon-based inks, the contrast can be dramatic. The MCI system can record large or small areas, allowing high-resolution mapping.

MCI has received a grant from the Smithsonian Women’s Committee to acquire a digital infrared imaging system. It is the first system of its kind in the Smithsonian Institution, allowing advanced non-destructive documentation of latent images.

Ultraviolet Imaging

Copybook in Visible Light

The left images are of a copybook illuminated and photographed using visible light and with Ultraviolet Radiation. The right images are looking closer at the text of the copybooks with both visible and ultraviolet light.

Ultraviolet radiation has been widely used in art conservation as a non-destructive examination technique. UV-induced fluorescence is used for the identification, characterization, condition assessment, and treatment of objects. It is particularly useful in the cases of organic materials such as plastics, coatings, and adhesives. The technique often shows alterations of objects over time, as in the case of varnishes on paintings.

While there is currently no standardization of the practice, there is general guidance available. Reporting of the illumination sources and other conditions is therefore very important.

UV-induced fluorescence technique can be documented using a digital camera. We have used the technique to record changes in objects, and to make documents legible (as seen above).