Cooper Hewitt’s object conservators’ technical study and conservation of the surtout de table (designed by Pierre-Phillipe Thomire, ca. 1805) in the museum’s permanent collection was recently presented at several conservation-focused conferences (including focuses on sliver-leaf mirror and gilt metal). Information about the treatments and special imaging techniques used to study the piece were also shared in an in-gallery digital interactive during the exhibition Tablescapes: Designs for Dining (on view at Cooper Hewitt October 2018–April 2019). This post serves to both archive the project and reach wider audiences to introduce how surface textures can be explored using interactive viewers. You’ll also find some background on the open-source imaging technique we used to examine the surfaces.

Conservation treatment of the surtout’s unstable silver-mirrored glass trays and gilt-metal and glass components (54 components in all) allowed for close observation of both the overall condition and manufacturing details of the elaborate work (see presentations linked above). Extensive finishing work using hand tools after the metal was cast (including chasing and burnishing) is present on all metal surfaces, allowing the hard material to mimic textures as varied as flesh, fur, and feathers. These finishing techniques also enrich the play of light across the surtout, with contrasting matte and shiny sections. To better understand these features, technical study utilized Reflectance Transformation Imaging (RTI). Here, you can view three of the interactive images produced using this technique. You can reposition the light in the interactive viewer to view light from different angles.

Taking a close look at of one of the classical female figures on the perimeter of the plateau, you can see the fine toolmarks used to create surface textures on the gilt brass surfaces. Feathers, skin, and textiles are each rendered with different patterns.

RTI documents and reveals hard-to-see surface details, with different details becoming visible as light shifts. The technique was developed by imaging scientists at Hewlett Packard, and was eventually released as an open-source tool available for researchers. After capturing a series of images from different light positions, the resulting files are processed using computer algorithms in the RTIBuilder open source software (available from Cultural Heritage Imaging). Two small, shiny, black spheres are included in the image to track the angle of light in each photograph. Combining many (approximately 40 to 80) photographs from different angles allows for an interactive relighting of the subject. RTI Viewer software or a web viewer is used to display the resulting composite files. The desktop version of the software also includes additional mathematical manipulation modes, which aid researchers in interpretation of surface textures.

In this detail of the leg and costume of one of the dancing figures on the centerpiece, you can see a contrast of fur and flesh textures. Fine linear strokes are used to simulate the fur texture, accompanied with pebbled fringe chiseled with a tiny point. On the thigh, in contrast, you can see fine irregular eccentric marks, probably made with a wire brush tool, suggestive of soft skin.

The grapevine at the top of the centerpiece has shiny, smoothly burnished grapes, in contrast to the veined grape leaves.

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