THE EXHIBITION OF UNLACQUERED SILVER AT THE METROPOLITAN MUSEUM OF ART
5 THE MARY AND MICHAEL JAHARIS GALLERY
In 2000 the medieval department's Early Christian, Byzantine, and Migration period collections were reinstalled in the newly designed Mary and Michael Jaharis Gallery. The changes in the exhibition space necessitated the fabrication of entirely new vitrines. Given the richness of the museum's collection of Early Christian and Byzantine silver and silver gilt archaeological objects and their variable states of preservation, it was an opportune moment to evaluate the system utilized for the Attarouthi Treasure and to consider expanding it to all of the vitrines exhibiting silver objects.
A principal goal underlying the new design for the Jaharis gallery was to open up and accentuate the shallow arches articulating the walls of the galleries. The vitrines, similarly sized to the original Attarouthi display, were suspended within the arches and projected slightly forward and to the sides, and were fabricated from aluminum sheet, 3/8 in. thick, with U-channel welded on for the insertion of the glass sides and top. Mechanical attachment was utilized for all metal-to-metal joins. Prior to assembly, 3/4 in. extruded polyethylene planks were attached to all interior metal surfaces with an epoxy adhesive and then fabric covered. Where increased strength was required for the mounting of heavy objects from the back panel, vertical aluminum posts were secured down the length of the reverse. All metal-to-metal joins were sealed with silicone, and glass-to-metal joins were gasketed. The angled support for the label copy across the front of the vitrine was powdercoated aluminum with the label copy itself adhered with 3M double-sided, laminating adhesive #465 to a thin sheet of Sintra Material, a rigid, closed-cell, polyvinyl chloride board. All of the materials used were tested in-house by the modified Oddy test (Bamberger et al. 1999).
When the original vitrine displaying the Attarouthi Treasure was deinstalled prior to the objects' incorporation into the Jaharis gallery, the pump's rubber diaphragm was found to have deteriorated, significantly reducing its effectiveness. An online search of small, special-purpose pumps, built to a higher material and operational standard, led to the selection of a miniature brushless pump in a sealed housing produced by Brailsford, incorporating diaphragms made either of Viton, a fluoroelastomer, or EPDM, an ethylene propylene diene monomer, both of which the manufacturer suggested replacing on a yearly basis due to possible fatigue. In discussions with Brailsford, Viton was chosen given its slightly greater stability; however, there is the potential for some minimal off-gassing from the diaphragm. That potential risk was acceptable given that the air within the display area of the vitrine is circulated within a relatively closed system. Any possible contaminants that might be given off by the pump's diaphragm, or diffuse into the air within the vitrine from the gallery will be filtered immediately in the case of the Viton or will be diluted by the conditioned air in the display area and eventually scrubbed by circulating through the filter. Indeed, the system had effectively mitigated any pollutants generated by the deteriorated rubber diaphragm in the initial installation. While the pumps are described as quiet, their installation in vitrines comprised only of glass and metal necessitated further reduction of the vibration to reduce the noise to acceptable levels. To add dampening mass, the pumps were attached to a thick plate of Plexiglas to adsorb vibration, and small feet of high density polyethylene were adhered to the bottom of the plate to reduce the surface area in contact with the vitrine.
Continuing research on adsorbents for gaseous pollutants has been limited. A study by Bradley 1989 at the British Museum led to the introduction of zinc oxide pellets as passive scavengers in their vitrines displaying silver. Several conservation-specific materials, Scavengel and MicroChamber were produced that incorporated different sorbents into plastic or paper matrices with a significant component of each being activated carbon. While these materials were considered, the proven ability of activated carbon to adsorb gaseous pollutants, the efficiency of a filter containing only sorbent, and the successful implementation of the system in the initial Attarouthi installation led to the continued use of activated carbon in the circulating filtration systems incorporated into the vitrines for the Jaharis gallery.
The need to be able to monitor the levels of contaminants within museums and vitrines had stimulated the development of both passive and active techniques for the detection of formaldehyde and other pollutants (Grzywacz and Stulik 1991; Landry et al. 1991; Martin and Blades 1994; Grzywacz and Tennent 1994); however, a means for the detection of hydrogen sulfide had not yet been addressed and led to the reintroduction of polished sterling silver blanks into the vitrines as visual indicators. The diaphragms and charcoal are changed on a yearly basis with pump failure monitored regularly in passing through the gallery. To date, the silver has shown no indication of tarnishing.