44th Annual AIC meeting, May 17, 2016, “An Unexpected Surface: Research and treatment of a 19th century mounted oyster shell by Froment-Meurice” by Emily Brown

This talk focused on the research and treatment of Froment-Meurice oyster shell artifact made by Emile Froment-Meurice.  The conservation concerns were identification of the corrosion layers and treatment of the metal surfaces.   The artifact was purchased by William Walters in 1878.  It is a composite artifact that depicts two putti discovering a pearl inside of an oyster.  The oyster shell holds a natural pearl in a metal mount.  The mermaid stem and putti are a silver copper alloy, the base is silver with a gold enriched surface and the hinge is a gold alloy.  The oyster shell artifact was damaged and repaired multiple times in the past.  The 1930 photograph from the museum shows the object in one piece.
The main condition issue for this treatment was the heavily tarnished metal surfaces.  The silver and gold elements were nearly black with heavy tarnish overall.  In the 1840s the goldsmiths would often intentionally create a darkened oxidized surface on silver.  In a 2003 French catalogue “Tresors D’Argent” (translated as “Silver Treasures”) two similar shell objects are included, but both have polished and shiny metal elements.  Other artifacts are listed as “oxidized silver and painted sheet metal” objects.  A similar oxidized silver surface can be found on the commemorative shield (c. 1881) by Froment-Meurice in the Art Institute of Chicago labeled as “an elliptical shield of oxidized silver”.
There are a few differences between tarnished silver and oxidized silver.  Tarnished silver is an unintentional patina created by airborne pollutants.  Oxidized silver is an intentional antiqued patination created by chemical compounds.  The small traces of silver chloride found on the surface of the artifacts may be a byproduct of silver chloride that was used to antique the surface of silver objects.  With this in mind, the decision was made to clean the silver, but not remove the black surface.  The gold elements would be cleaned until bright.
The gold and gilt silver components could not be cleaned with abrasion or normal polishing.  Instead an acidified thiourea xantham gum gel was used to clean the surface.  The gel as applied with a cotton pad and rinsed with water.  The dwell time was kept to a quick 5 – 10 seconds.  The process was repeated as needed.  For the metal clasp, mylar was placed between the metal and the shell to protect the surface of the shell.  The gel was applied with a brush and then rinsed with the use of chem-wipes and a bristle brush.  The gel cleaning produced a bright and shiny surface.  The process had excellent control and a quick removal of the material was possible.  The putto were adhered into place, but the shell was left partially unassembled for transportation.  A complex and well-designed storage and shipment box was created for the artifact.  This storage box was featured in the STASH flash III on May 14^th and will be published on the AIC STASH website.