43rd Annual Meeting- Research and Technical Studies, May 16, The Technical Study and (Re-)Restoration of a Limoges painted Enamel Plaque, by Gregory Bailey

Gregory Bailey, Assistant Conservator of Objects at The Walters Art Museum, detailed the technical and historically-sensitive characterization of restorations on a Limoges painted enamel plaque at the Metropolitan Museum of Art (32.100.263), undertaken to correct the object and its record.
In this case, the correction required was literal. The oval plaque depicts Diana and Proserpina in a nocturnal scene, encircled by a border inscription. The object was accessioned by the museum in 1931 and thereafter underwent several treatment campaigns, during which repainting of the border yielded the nonsensical phrase “ESTES PARVBIQVITE.” Curatorial research identified the original motto as “POTESTAS PAR VBIQVE,” and Greg’s task was to restore this motto to the border.
To do so, he masked the incorrect text rather than replaced it. The mask was made by casting Orasol-toned HXTAL epoxy into a two-part transparent PVC mold. The PVC mold was created using a dental vacuum former over a cast plaster mold of the enamel area. Once cured, the epoxy was removed, trimmed, and adhered with Paraloid B-72 over the restoration at the plaque’s rim. The final fill is therefore removable with very little solvent, and the correct (original) motto was inpainted with acrylics. Simply over-painting the text would have compromised the solvent-sensitive 19th-century restoration areas, and erased this campaign from the plaque’s history.
Technical analyses that preceded this treatment provide information about the original and restoration materials, as well as their working methods. The plaque is composed of opaque and transparent enamels over a  copper support, with surfaces partially silvered and gilt.
Greg notes that reflected long wave ultraviolet photography is not often used in object examination because it requires special quartz optics. The technique is useful for painted enamels because certain colorants and enamel compositions are partially or completely transparent to UV radiation, yielding information about the layered structure and sequence of enamel application . For example, the cobalt blues and lavender enamels on the plaque appear transparent under such radiation, making visible the underlying painted enamel structures and the silver foils. Short wave ultraviolet-induced visible fluorescence photography shows some fluorescence of the lead containing enamel colors, and of the restoration varnish. Long wave ultraviolet induced fluorescence shows the restoration varnish more clearly, as many early varnishes fluoresce bright green, suggesting the presence of a natural resin. (This plaque was also varnished in 1993 with dammar, also a natural resin, whose florescence instead appears faint milky blue due to the addition of light stabilizers to the varnish). Reflected near infrared photography shows the layered structure of cold painted restoration enamel, as again, certain enamel compositions and colorants are more transparent to infrared than others (ex. reds, yellows, oranges). Typically, those transparent to ultraviolet radiation are different from those transparent to infrared, making the two reflected radiation techniques complimentary. Greg also notes that reflected infrared is good for identifying cracks in counter enamel because cuprite often forms along these divides, which reflects strongly in the infrared range.
X-ray fluorescence spectroscopy (XRF) was used to signal compositional differences between the original and fill enamel materials. Generally, the restoration enamels contain a significant lead component as compared to the original enamel. The white restoration enamel contains lead arsenate, not in use until the 18th-century, and tin oxide as opacifiers. The green and blue restoration enamels contain chromium, a colorant not utilized in enamels before the 19th-century. The pink flesh tones contain zinc, which is associated with pink and red 19th-century enamels, but may have also been used as a low melting point flux of thin wash applied over the white enamel.  Lastly, the translucent restoration red enamel is colored in part by antimony oxide, rather than the traditional use of copper oxide reds.
All of the restoration enamels are similar in composition and were likely applied during the same 19th-century campaign; however, different application methods were likely used.  X-radiography illustrates a solder seam concealed by varnish at the lower edge where new enamel was laid over the copper support, which was then a common structural repair method. Elsewhere, however, enamel patches are set into losses over silver foil that appear neither soldered nor scored. These may have been painted and fired in place, cold painted in place, or painted and fired separately and then adhered in place. Greg notes that the plethora of active enamel restorers in the 19th-century surely led to the evolution of new restoration techniques. This plaque serves as an example and impetus to further document such developments.
Greg’s talk serves as a reminder that our understanding of an object, even one fortunate enough to have been previously treated and studied, is ever-evolving with the application of new analytical technologies and refreshed methodologies such as those expertly used here.