the exhibition of unlacquered silver at the metropolitan museum of art

Maney Publishing

The Exhibition of Unlacquered Silver at the Metropolitan Museum of ArtAuthor(s): Pete DandridgeSource: Journal of the American Institute for Conservation, Vol. 44, No. 3 (Fall-Winter,2005), pp. 175-183Published by: Maney Publishing on behalf of The American Institute for Conservation of Historic &Artistic WorksStable URL: http://www.jstor.org/stable/40025149 .

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THE EXHIBITION OF UNLACQUERED SILVER AT THE METROPOLITAN MUSEUM OF ART

PETE DANDRIDGE

ABSTRACT - The desire to inhibit the rate of

tarnishing of silver objects has often led to their surfaces

being coated with a lacquer or varnish; however, there are occasions when such a treatment would be inappro- priate, either placing the object at risk physically or

inhibiting the visual perception of its surfaces. Both concerns have been operative at the Metropolitan Museum of Art over the course of the last 25 years and have resulted in the implementation of several different

approaches to the display of unlacquered silver. In each

instance, these efforts were stimulated by the installation of different parts of the museum's collections, initially in the American Wing, followed by the Byzantine treasure from Attarouthi, and most recently, the medieval

department's Early Christian and Byzantine silver. A common goal throughout has been to minimize the effects of gaseous pollutants on the silver by creating "clean" vitrines or storage cabinets, and then integrat- ing into these spaces either passive or active systems to further reduce the levels of possible contaminants. The

specifications for the vitrines and the techniques used for diminishing the gaseous pollutants evolved inter-

nally in conjunction with a growing body of research in preventive conservation focused on identifying both the harmful materials within exhibition and storage environments and the means by which a more benign environment might be achieved. A review of the deci-

sion-making which governed these various installations reveals a common approach which took into account a

greater understanding of the dynamics of silver corro-

sion, and the introduction of new materials and

methodologies with greater effectiveness in the adsorption of gaseous pollutants. The description of successes and failures in the implementation phase may benefit those faced with similar concerns in the exhibition of their collections.

TITRE - L' exposition de F argent non verni au

Metropolitan Museum of Art (musee d'art metropolitain). RESUME - Le besoin de ralentir le rythme du ternissement des objets en argent a souvent eu comme

consequence l'application de vernis ou de laques sur leurs surfaces; cependant, il existe des situations pour lesquelles un tel traitement est inapproprie, soit en occasionnant un risque pour l'objet a vernir ou en diminuant la perception esthetique de ses surfaces. Ces deux preoccupations ont ete en vigueur au Metropolitan

Museum of Art au cours des 25 dernieres annees et ont conduit a la mise en application de plusieurs approches pour la presentation de l'argent non vernis. Dans

chaque cas, ces efforts ont ete stimules par l'installation de differentes parties de la collection du musee, au tout debut pour l'aile americaine, ensuite par le tresor

byzantin d' Attarouthi et plus recemment, les pieces d'argenterie byzantines, des touts debuts de la Chretiente et de la periode medievale.Tout au long de ce processus, l'objectif commun a ete de minimiser les effets des polluants gazeux sur l'argent en creant des vitrines ou des cabinets d'entreposage"propres", et d'y integrer ensuite des systemes actifs ou passifs pour reduire davantage le niveau de contaminants. Les specifications des vitrines ainsi que les techniques utilisees

pour diminuer les polluants gazeux ont progressive -

ment evolue parallelement avec plusieurs recherches en conservation preventive. Ces recherches avaient comme objectif, a la fois Identification des materiaux

dommageables dans les expositions et les reserves, ainsi

que les moyens par lesquels un environnement plus acceptable pourrait etre obtenu. Un examen du

processus de decision qui a gouverne ces divers projets revele une approche commune qui incorpore une bonne comprehension de la dynamique de la corrosion de l'argent, ainsi que l'introduction de nouveaux materiaux et des methodologies presentant une meilleure capacite d'absorption des polluants gazeux. La description des succes et des echecs de notre mise en oeuvre pourra etre benefique pour ceux qui ont des

preoccupations similaires lors de la mise en valeur de leurs collections.

TITULO - La exhibicion de plata sin laca en

Metropolitan Museum of Art (Museo Metropolitano de

Arte). RESUMEN- El afan por inhibir la velocidad de ennegrecimiento de los objetos de plata a menudo ha llevado al recubrimiento de sus superficies con

alguna laca o barniz; sin embargo, en ocasiones estos tratamientos podrian ser inapropiados, ya sea porque hacen peligrar al objeto fisicamente, o porque inhiben la percepcion visual de sus superficies. Ambas preocupaciones se han tornado en cuenta en el Museo

Metropolitano de Arte a traves de los ultimos 25 afios,

y han resultado en la implementacion de varios enfo-

ques diferentes para la exhibicion de plata sin laca. En cada instancia, estos esfuerzos fueron fomentados por

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PETE DANDRIDGE

la instalacion de diferentes partes de las colecciones del museo, inicialmente en el American Wing (Ala Americana), seguida del tesoro bizantino de Attarouthi, y mas recientemente, la plata del periodo cristiano temprano y bizantina del Departamento Medieval. Un proposito comun en todos estos casos ha sido minimizar los efectos de contaminantes gaseosos en la plata mediante la creacion de vitrinas "limpias" o armarios de almacenamiento, y luego integrar a estos espacios sistemas pasivos o activos para reducir aun mas los niveles de los posibles contaminantes. Las especificaciones para las vitrinas y las tecnicas usadas para disminuir los contaminantes gaseosos evolucionaron internamente en conjunto con un creciente aumento de investigaciones en el campo de la conservacion preventiva, enfocado a identificar tanto los materiales nocivos que se encuen- tran dentro de los ambientes de exhibicion y almacenamiento, como los medios para lograr un ambiente mas benigno. Una revision de las tomas de decisiones que rigieron estas distintas instalaciones revela un enfoque comun, que tomo en cuenta un mayor entendimiento de las dinamicas de la corrosion de la plata y la introduccion de nuevos materiales y metodologias con mayor efectividad en la adsorcion de contaminantes gaseosos. La descripcion de los exitos y fracasos en la fase de implementacion podria beneficiar a aquellos que enfrentan preocupaciones similares en la exhibicion de sus colecciones.

TITULO - Exposicao de prataria nao envernizada no Metropolitan Museum of Art (Museu Metropolitano de Arte). RESUMO - O desejo de inibir o grau de

enegrecimento de objetos de prata muitas vezes levou a se cobrir suas superficies com laca ou verniz; no entanto, ha ocasioes em que este tipo de tratamento seria inadequado, seja por colocar o objeto fisicamente em perigo, ou por inibir a percepcao visual de sua aparencia. Ambas as preocupacoes foram exami- nadas no Metropolitan Museum of Art (Museu Metropolitano de Arte), no decorrer dos ultimos 25 anos, e resultaram na implementacao de diversas

abordagens diferentes para a exibicao de prataria nao envernizada. Em cada caso, esses esforcos foram estimulados pela instalacao de diferentes partes das colecoes do museu, inicialmente na ala americana, seguida pelo tesouro bizantino de Attarouthi e, mais recentemente, a prataria primitiva crista e bizantina do departamento medieval. Um objetivo comum em toda parte tern sido minimizar os efeitos dos gases poluentes sobre a prata atraves da criacao de vitrines

"limpas" ou gabinetes de armazenagem, e depois integrando, dentro desses espacos, sistemas ativos ou

passivos para ajudar a reduzir os niveis de possiveis contaminantes. As especificacoes para as vitrines e as tecnicas usadas para diminuir os poluentes gasosos desenvolvidos internamente, em conjunto com um crescente aumento da pesquisa em conservacao

preventiva, focaram em identificar tanto os materiais nocivos dentro dos ambientes de exposicao e

armazenagem, como os meios pelos quais pode ser obtido um ambiente mais benigno. Uma revisao do

processo de decisao que controla essas varias insta- lacoes revela uma abordagem comum que permitiu uma maior compreensao da dinamica da corrosao da

prata e a introducao de novos materiais e metodolo-

gias com maior eficacia na adsorcao de poluentes gasosos. A descricao dos sucessos e fracassos na fase de

implementacao pode beneficiar aqueles que se defrontaram com preocupacoes similares na

exposicao de suas colecoes.

1. INTRODUCTION

Over the past 50 years, conservators and conservation scientists have focused increasingly on identifying materials in the museum environment that contribute to the deterioration of works of art and the mecha- nisms by which they work. Much of the initial research was generated by the packing industry (Packman 1957, 1960; Ranee and Cole 1958; Clarke and Longhurst 1961; Ami et al. 1965; Donovan and Moynehan 1965) with conservation scientists and conservators supple- menting and refining the scope to reflect the specific needs and conditions of the museum community. The

susceptibility of silver and metals generally to the effects of acidic pollutants generated by the materials used in their display and storage has been a subset of that research (Thomson 1965, 1978; FitzHugh and Gettens 1971;Weyde 1972; Oddy 1975;Blackshawand Daniels 1978, 1979; Hnatiuk 1981; Leveque 1986; Berndt 1987; Craddock 1988; Brimblecombe et al. 1992; Green and Thickett 1994; Lee and Thickett 1996; Hatchfield 2002;Tetreault 2002). As a result, the

understanding of the "ideal" macro- and microenvironments for the exhibition of metals has grown substantively over time; however, economic and aesthetic concerns often inhibit museums' abilities to create the model environment. Such constraints have necessitated the development and institution of a vari-

ety of less costly but effective measures that are either

object or exhibition case specific. A historical

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overview of the different approaches taken during the

past 25 years by the Metropolitan Museum of Art to the exhibition of silver is illustrative of the techniques utilized by conservators to enhance the safekeeping of silver on display or in storage.

2. THE ERA OF LACQUER

Since at least the early 1950s, the principal form of protection for decorative and archaeological silver in the collections of The Metropolitan Museum of Art from the effects of contaminants in the air has been a

coating of Agateen #27, a nitrocellulose lacquer, diluted with Agateen Thinner #1 and applied as a

spray or by brush over a cleaned and degreased surface. Given its physical and optical properties, a

properly applied coating can be an effective barrier (De Witte 1973-74; HeUer 1983; Reedy et al. 1999); however, an excessive build-up of lacquer can dimin- ish the reflectance of a burnished silver surface or

impair the viewer's ability to accurately read finely chased or engraved details. Of further concern is the

potential regular process of removal and reapplication necessitated by the effective lifespan of such a coating. While many objects are in stable enough condition to be treated repeatedly, there are other, more fragile pieces whose previous conservation treatments might be reversed by the action of the solvents or whose surfaces might be too sensitive for any mechanical

agitation. By eliminating the need to lacquer silver, such problems can be avoided, as can the investment in time and resources repeated conservation would

require.

3. THE AMERICAN WING

During the late 1970s and through much of the 1980s, The Metropolitan Museum of Art undertook a series of capital building projects to rehouse both the

Egyptian and the American Paintings, Sculpture and Decorative Arts collections, as well as to install the Rockefeller Collection of Primitive Art. Coincident with the expansions in physical spaces was a philo- sophical change in the way the collections were to be exhibited. Not only were the most significant objects in the collection to be rehoused, but also those pieces that had previously been inaccessible would now be made available to the general public in areas adjacent to the main galleries.

Of particular interest for this study were the two different systems established in the American Wing

for displaying silver without a coating (Weintraub 1981, 1988) in response to the two approaches taken by the curators for displaying the collection. In 1981, the principal silver objects were organized themati- cally around the balcony overlooking the Englehard Court in freestanding vitrines fabricated by Glasbau Hahn. The bulk of the collection was then installed for study and storage in 1988 in a distinct area, The Henry R. Luce Center for the Study of American Art, within two large, floor-to-ceiling cases. In both installations, all structural elements were specified as glass and metal both for aesthetic reasons and to avoid wood and wood products and their associated acidic vapors.

The vitrines around the balcony were designed to restrict the influx of outside air. The three glass panels that defined the sides and back of each vitrine were joined to one another with epoxy. The joins along each side were strengthened and warpage inhibited by overlaying the vertical edges of each panel with strips of glass similarly adhered. A gasketed sliding glass panel across the front provided access to the interior. The top and bottom edges of the glass panels slotted into metal channel associated with the metal framework for the light attic and the metal base of the vitrine. Design concerns necessitated that the interior shelves, blocks, and decks in the balcony cases be fabricated from MDO, exterior grade plywood with phenol-formaldehyde adhesive, and covered with a dyed cotton fabric. To counteract the acidic gases that might off-gas from the plywood and to provide a buffer against the influx of outside air, 3M strips of powdered, activated carbon cast out on a vinyl base were attached to the underside of all the shelves. The manufacturer changed the formulation of the strips early on to eliminate the plastic substrate and introduced Tarni-Shield with the activated charcoal embedded in a paper matrix.

The capacity of activated carbon to adsorb gaseous pollutants harmful to metals was understood early on in the packaging industry (Ranee and Cole 1958). Its use was advocated by the conservation community initially as filters to be inserted into HVAC systems as a means of reducing the levels of outdoor pollutants allowed into the ambient air of the gallery (Thomson 1965, 1978; Garver 1968). The introduction of activated carbon as a passive sorbent for gaseous pollutants into the interior of vitrines appears to have first been suggested by Padfield (1966) and became the standard approach to the reduction of acidic gases in storage and display (Oddy

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PETE DANDRIDGE

1975; Leveque 1986; Gilberg and Cook 1987; Craddock 1988; Druzik 1991; Weintraub and Wolf 1995; Lee andThickett 1996).

While the Luce Center was under construction, the silver not on display was stored, unlacquered, in interior metal and glass cabinets equipped with externally mounted, positive pressure systems to supply conditioned air to the interior of the cases (Weintraub 1981) at a flow rate sufficient to restrict the intrusion of outside air. The pump was installed adjacent to the case and pushed a steady supply of ambient air through Tygon tubing into the cases. In- line canisters of silica gel and Purafil, a potassium permanganate and alumina-based material, controlled the relative humidity and adsorbed gaseous pollutants. An advantage of the Purafil over the activated- carbon was that it was self-indicating, changing color when its saturation point was reached.

When the Luce Center was completed and the silver moved from the storage cabinets to its permanent home, the silica gel component was eliminated from the system, and larger pumps were utilized to accommodate the more generous, open spaces. The silver was displayed both on glass shelves and on formed metal shelving with a baked-on powder- coated finish. Brush gaskets adhered to the edges of the adjoining glass panels allowed the pressure to equalize.

In evaluating the two systems, an obvious appeal of the use of a passive approach was its lack of dependence on a mechanical system, but it placed a premium on the relative exclusion of outside air, the creation of an interior vitrine environment that was non-reactive, and the regeneration or replacement of the adsorbent prior to its saturation point. Depending on the surface area of the sorbent and the presence of other surfaces that might scavenge pollutants, the exhibition silver can act as a sink for hydrogen sulfide (Parmar and Grosjean 1989, 1991; Druzik 1991) such that tarnishing may eventually initiate. The experience in the American Wing seems to bear this out in that the silver has shown visual indications of sulfide tarnish, albeit at a slower rate than if no adsorbent were present.

Several factors have inhibited the success of the positive pressure system. The constant cycling of the pumps, and their sizing relative to the resistance of the tubing surface and the sorbent, necessitated their replacement every two years. Of equal concern was that the noise generated by the pumps was considered to compromise the visitor's experience. Since there

was no alternative space for the pumps' installation, their use has been discontinued and a system of

passive adsorption with canisters of activated carbon substituted; however, the size of the cases, the relatively minimal surface area of the sorbent, and the ease with which ambient air can enter the display area have all limited the protection afforded the silver.

4. THE ATTAROUTHI TREASURE

In 1986, the museum acquired the Attarouthi Treasure, a group of sixth-century, Byzantine, partial gilt, silver, repousse objects including chalices, censers, and a Eucharistic dove in such a state of

preservation that they came close to representing the

original surface quality intended by the goldsmiths (Dandridge 2000). As documents of the visual aesthetic current at the time, it was important to present them to the public and scholars in as unblemished a state as possible. Further, the fragility of the gilded surfaces in discrete areas on the chalices had necessitated localized consolidation with Paraloid B-72, an

ethyl methacrylate and methyl acrylate copolymer, precluding their being lacquered and subsequently cleaned without potential disruption and loss of the reattached gold leaf.

In preparing the specifications for a vitrine to house the treasure, elements of both design schemes utilized in the American Wing were adopted while

incorporating several new products and introducing an active, recirculating, filtration system. Hahn fabricated the vitrine with the display area a box of glass and metal with a volume of sixty-four cubic feet, supported by a wooden base, with light supplied externally from an attic overlaying the glass top. Apart from the front panel that provided access to the interior, all glass-to-glass and glass-to-metal joins were secured via aluminum channel with inset silicone gasketing. As supplied, the contact between the front panel and the glass sides was not gasketed, and due to the size of the glass, the panel exhibited a

slight bow. To provide a gasket and to close the space created by the bow, a bead of clear, neutral cure silicone caulk was run into the gaps down either side of the panel. Once cured, each bead was sliced through its center to allow the door to be opened and closed. Interior decks and blocks were made from extruded, high-density polyethylene foam, a product utilized in the packaging industry and suggested by Blackshaw and Daniels (1978) as a material appropriate for the

storage of objects. A distinct advantage of the mate-

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rial as supplied by Sentinel Foam Products was that it was produced in plank form in a variety of densi- ties. The 9PCF weight was selected since it could be

shaped with woodworking tools, joined mechani-

cally with screws, and allowed for fabric coverings to be attached with staples, eliminating any need for

glue. Depending on the thickness of the material, it can distort under the strain of stretched fabric; however, this characteristic can be offset by attaching the foam to more rigid materials such as aluminum channel, L-bracket, metal sheeting, or Plexiglas. In this instance, the full two-inch depth of the material could be accommodated for the backing board and

required no auxiliary support. The interior label copy was adhered with wheat starch paste to eight-ply acid-free ragboard. All materials had either been

approved for permanent exhibition by the Getty Conservation Institute (1989) or by means of the

Oddy test (1975) at The Metropolitan Museum of Art.

Two different approaches were investigated to

actively condition the air within the vitrine, the reduction of the relative humidity to levels suffi-

ciently low to inhibit the production of silver sulfide, and the elimination of hydrogen sulfide and other acidic vapors with an adsorbent. Michalski (1982, 1985) andToogood and Wilson (1985) had designed modules that constantly reconditioned the air within a vitrine to a predetermined relative humidity. While successful, both systems contained multiple mechanical elements and required an adjacent space for installation not available in the Byzantine gallery. Given the inert quality of all of the vitrine materials and an ambient relative humidity of 40-50% in the galleries, it seemed more appropriate and practical to imple- ment the second approach and focus on purging the

atmosphere within the vitrine of those organic acids known to be most deleterious to silver.

The research undertaken by Parmar and Grosjean (1989, 1991) to study the effectiveness of sorbents in

removing atmospheric pollutants from the exhibition environment quantified for the first time the relative

capacity of a variety of sorbents including Purafil and activated carbon to successfully adsorb hydrogen sulfide in both the passive and active mode. For

adapting an active system of filtration within a vitrine, they suggested using a fish tank pump in conjunction with a canister of activated carbon. Their system was

adapted and a fish tank pump was installed in the base to constantly circulate the air in the display area

through Tygon tubing and an in-line canister filled

with 200 grams of activated carbon. A 12-20 mesh size was selected for the sorbent to maximize the surface area for adsorption, and at the same time minimize both the drag on the flow of air through the canister and the migration of dust into the exhibition space. A loose packing of cotton wool in the supply side of the filter served as a catch for any particulates. The tubing was inserted through holes drilled in the aluminum base of the bonnet with the voids around the tubing filled with a neutral cure silicone caulk. The minimal noise and vibration of the pump were dampened by the plywood surround of the base and by setting it into a foam box.

Since there is no visual indication of when activated carbon has reached its saturation point, an alter- nate means of evaluating conditions within the vitrine needed to be found. No active or passive monitors were available for detecting hydrogen sulfide at the levels that might affect silver. Blackshaw and Daniels' (1979) analysis of the relative rates of corrosion of different silver alloys indicated that polished blanks of sterling silver were more reactive than pure silver as well as comparable alloys worked in a more traditional manner. Two polished blanks of sterling silver were placed on the deck adjacent to the ports for air supply and return with one half of each blank brush coated with two applications of Agateen #27 diluted in Agateen Thinner #l.An arbitrary time frame of one year was scheduled for the replacement of the sorbent. The condition of the silver surfaces was monitored on a regular basis and over the course of the next nine years no visual change was percepti- ble either on the blanks or on the surfaces of the objects. While no data log was recorded for the relative humidity levels within the vitrine, periodic meas- urements in the gallery confirmed the expected range in ambient conditions of relative humidity, broken only by slight fluctuations at points of seasonal transi- tion.

5. THE MARY AND MICHAEL JAHARIS GALLERY

In 2000 the medieval department's Early Christian, Byzantine, and Migration period collections were rein- stalled 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

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PETE DANDRIDGE

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 powder- coated aluminum with the label copy itself adhered with 3JV1 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 ofViton, 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 tech-

niques for the detection of formaldehyde and other

pollutants (Grzywacz and Stulik 1991; Landry et al. 1991; Martin and Blades 1994; Grzywacz andTennent 1994); however, a means for the detection of hydrogen sulfide had not yet been addressed and led to the rein- troduction 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.

6. CONCLUSION

The need to display silver objects without having to

lacquer them has led to the fabrication of a group of sealed vitrines from materials selected to create a

benign interior environment. The inclusion of an active filtration system in the design provides a significant degree of protection against pollutants from external sources and from any which might be off-

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gassing from the vi trine materials. The system has functioned successfully for fifteen years in the instance of the Attarouthi Treasure. What is not clear is whether a passive system of adsorption utilizing either activated charcoal or another of the sorbents now being tested (Ankersmit et al. 2000) would be equally successful given the relatively inert environment of the vitrine. Recent developments in accurately recording the dose of hydrogen sulfide or carbonyl sulfide within a closed space (Ankersmit et al. 2000) may help to clarify the

question. Certainly, the minimal cost of an active filtration system provides a measure of assurance, as well as providing a potential means for exhibiting unlacquered silver in vitrines built more economically and to different standards.

ACKNOWLEDGMENTS

The author would like to acknowledge the generos- ity of the Getty Conservation Institute for making available the results of their material testing; the efforts of Tom Vinton, Principal Departmental Technician in the Medieval department for his assis- tance in the maintenance of the filtering systems; and the support of Helen Evans, Curator, Department of Medieval Art, Frances Safford, Associate Curator, Department of American Decorative Arts, George Wheeler, Research Chemist, Department of Scientific Research, and Lawrence Becker, Sherman Fairchild Conservator in Charge, Sherman Fairchild Center for Objects Conservation.

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SUPPLIERS

Vitrines: Glasbau Hahn Hanauer Landstrasse 211 D-60314 Frankfurt/Main Germany (+49) 69 94417 - 0

Pump:TD-4NA (1): Brailsford & Company 15 Elm Avenue Antrim, NH. 03440 (603) 588-2880

Sentinel Foam Products Division of Packaging Industries Group, Inc. Hyanms, MA 02601 (617) 775-5220

Activated Carbon: Sigma-Aldrich (800) 325-3010

PETE DANDRIDGE is Conservator in the Sherman Fairchild Center for Objects Conservation, where he began working in 1979. He received his MA in conservation and a certificate of advanced studies from the Cooperstown Graduate Program in the Conservation of Historic and Artistic Works of Art. Since 1984, he has had primary responsibility for the ivories, enamels, and metalwork in the collections of the Department of Medieval Art and The Cloisters. He has published and lectured on Byzantine ivories, the gilding of silver in Byzantium, Early Christian and Migration Period jewelry, Limoges enamels, medieval aquamanilli, and related subjects. Address: Sherman Fairchild Center for Objects Conservation, The Metropolitan Museum of Art, 1000 Fifth Ave., New York, NY 10028; pete.dandridge@metmuseum. org

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the exhibition of unlacquered silver at the metropolitan museum of art

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