What Exhibits Can Do to Your Collection*

What Exhibits Can Do to Your Collection*

by CATHERINE NICHOLSON

Every institution mounting exhibitions of original documents, artifacts and art has good reason to be, concerned about the conservation implications and effects of exhibition on the displayed materials. The focus of this essay is on the situation in archives and libraries where items are not necessarily or even usually housed so as to assure readiness for display. They are often not matted or even encapsulated. They may have spent much of their existence folded, rolled, filed or shelved.

Making the Best of It

When one is answering the question posed in the title of this essay, a number of very real potential dangers to collections come to mind. But there can also be conservation benefits to items chosen for display in a well-run exhibition program. To start on a positive note, one can cite the potential benefits to collection items before proceeding to stories of danger and irreparable damage. These comments are based on experience with exhibition and loan activities at several institutions with both history and fine arts collections. Most of these issues and problems arise in a wide range of settings and can be amply illustrated by examples from many types of institutions.

Exhibition programs have a way of setting and driving an institution's conservation priorities. The impetus to mount exhibits generally is to show oif items in the collection and to reflect well on the institution or collection custodian. Most exhibit planners want the displayed items to look well cared for. Items planned for exhibition may finally come to a conservation lab for long-postponed conservation treatment. The process of exhibit research may uncover other neglected or damaged items that also require conservation care or improved housing'. Having a realistic exhibition schedule with items selected months in advance provides an impetus and urgency to getting treatment accomplished or housing improved, yet allows adequate time for carefully

* This text was firsl presented al the 1990 NARA Conference in Washington, DC, USA: Exhibits

and Preservation: A Delicate Balance.

thought-out and documented conservation treatments. Most conservators prefer to review a preliminary list of items many months prior to an exhibit rather than a belated final list, when the opening is so soon that there is no time for adequate treatment and it may even he difficult to veto a particularly damaged or vulnerable item.

Now if exhibition programs tend to set conservation priorities, it is the items chosen for display that have been given priority in the competition for scarce conservation resources. If the exhibition program draws on an institution's treasures and important pieces, then conservation resources are being allocated to items of great importance. If exhibitions systematically explore various important areas of your holdings or present surveys of holdings (such as a single artist or manuscripts by a significant individual or group), then those conservation resources may reach a wide though possibly shallow range across the collection. On the other hand, if exhibitions tend to include much ephemera or many borrowed items, then conservation resources may be diverted to lesser collection items or noncollcction materials. Exhibition conservation often consists of treatment or work on isolated items drawn from a much larger body and thus conservation attention is diverted from systematic care to a scattered, piecemeal approach. If several or many of a group of related items are being prepared for display, it is worthwhile to give the same treatment to the remaining items, to ensure that an entire related group receives consistent conservation care.

Preparing Exhibits

Preparing exhibits in many archives, libraries, and history museums probably requires more effort than in fine arts museums, because collections are not generally stored in a condition ready to go on exhibition in a frame or case. Most art museums arc able to house much of their collections already matted and find it economical to use the same mat both as a storage enclosure and for display.1 Some use a cover board or double window mats so that the outer cover or window mat with the inevitable smudges from handling can be folded behind to reveal a pristine inner window mat.2 Few museums have the resources to choose to remat every item for each exhibition. Ideally, such rematting is carried out keeping the print or drawing permanently hinged to a two-ply matboard insert that can be hinged into a fresh window mat without the effort and possible risks of repeatedly rehinging the original. 3

The matboard used for temporary exhibit support and permanent housing should be of museum or archival quality and consist only of laminates of either 100% cotton paper, also called rag paper, or of paper purified to remove

lignin. A rule of thumb is that the cut edge of the mat board should show layers of the same paper from top to bottom. A contrasting, tan-colored core paper is a sign of lignin-conlaining paper that, with time, can cause disfiguring stains. The presence of a so-called buffer or alkaline reserve of calcium carbonate in the matboard is considered beneficial for most documents. A variety of such buffered lignin-free matboard is available in most countries.

Simple archival displays mounted in flat cases may require no more preparation than cutting matboard sheets on which to rest the documents. But many exhibitions rely on matted or vertically mounted items that require a mounting system to support the paper. There are a number of ways of attaching items into mats. Japanese tissue paper hinges applied to the object verso with specially prepared pure wheat starch paste are the norm in many North American collections permanently matted for storage. But if mats must be removed after display or if the item is a two-sided document, a manuscript., a music sheet folio or borrowed, the curator, archivist or owner may object to paper hinges being attached at all or being left in place after exhibition. Since hinge removal can be a slow and painstaking process, a number of alternative mounting systems are in use, including the Library of Congress polyester sling*1 and custom-made edge or corner supports of paper or polyester film. Great care in placing and in removing corners and edge supports is needed to avoid possibly cutting or nicking the paper artifact. On some soft or damaged papers, they should never be used. Corners should be sized large enough to give adequate support and to avoid strain at vulnerable points such as old mends, losses, tears, etc. For this reason, ready-made corners have to be evaluated carefully and larger custom-made corners may be necessary.

A display support system that the National Archives of the United States has used for the past several years is exhibition encapsulation with wide margins beyond the bondline joining the two polyester film sheets. The wide margins can be taped onto the mat for exhibit, taking care that no tape is allowed adjacent to or inside the bondline. After display, the margins and all tape are trimmed away, leaving the item encapsulated and ready to return to storage. It is very important not to apply any tape or adhesive behind the encapsulated item itself, first, because it will be difficult to remove the item safely from its display mat, and further, because transparent tape and residual adhesive may be overlooked and adhere to adjacent items once returned to storage.

The film used for encapsulations, as well as for polyester slings and corner mounts, is polyethylene terephthalate polyester film, a strong, stable plastic sheeting made without plasticizers and with excellent aging properties, available under trade names including Melinex 516 (ICI), Mylar type D (DuPont), Scotchpar industrial grade polyester film (3M), and Hostaphan (Hoechst).

Polyester film has been in use for two decades to protect paper artifacts in sealed encapsulations as well as in partially sealed sleeves. The stability of such encapsulated or sleeved paper has been tested by accelerated heat aging. Although the results are as yet unpublished, the data indicate that aging properties are better when an alkaline reserve is included within a polyester enclosure, either by alkalizing the paper artifact or by including a paper sheet with an alkaline reserve. Polyester encapsulations and enclosures can be welded with special equipment, that uses either an ultrasonic head that travels along a track or a heated metal ribbon that fuses the sheet edges together. Since this equipment represents a major investment for many institutions, common alternatives for scaling sheets together in-house include a stable double-sided adhesive tape. Tape no. 415 (3M), or the use of a zigzag sewing machine.

Exhibition encapsulation provides several advantages, it protects the item from possible rough or hurried handling. It securely supports folded folios and fragile or tattered sheets. Heat-sealed or ultrasonically scaled encapsulations will support multi-paged pamphlets or booklets without problems of sagging or drooping. Tape-sealed encapsulations should not be attempted with bulky or heavy items, as the tape bond will fail, allowing the item to drop into the adhesive. Tape-sealed encapsulations are also not advised in very warm climates if the facility is not air conditioned 24 hours a day, again because of the possibility of bond failure.

As mentioned above, when items are encapsulated in this way for exhibition and ultimately for storage, it is important to deacidify the items whenever possible or to insert alkaline paper into the encapsulation to prevent sealing an acidic document in a closed environment, which can then accelerate acidic degradation. On the other hand, polyester film encapsulations will greatly reduce the exchange of air and water vapor, protecting sensitive documents from less than perfectly controlled temperature, relative humidity or the presence of external gaseous pollutants. There is also some evidence that polyester slightly reduces the transmission of visible and ultraviolet light. Encapsulations do give a margin of safely, but one still needs to be concerned about light levels and ultraviolet filters. Though encapsulation has a number of advantages from the standpoint of convenience, efficiency and protection, there are items for which other mounting approaches are desirable: original artwork, paper with a rich surface texture or undulating topography, deeply embossed letterpress printing and velvety silk-screen textures. In addition, polyester film can develop a strong static charge, which poses a risk of lifting very friable media, such as pastel, flaking gouache and powdery paints. Alternatives to polyester encapsulation must be used with such vulnerable materials.

In using exhibition encapsulation as a mounting system, it. is important to

use polyester film of adequate thickness to minimize distracting waviness and reflection of the polyester film. Generally 75-μm (3-mil) film is acceptable for small items up to 20 x 30 cm, but 100-μm or 125-μm film is less noticeable on larger items. When the polyester film touches the glazing, distracting diffraction patterns (irregular darker and lighter areas) will be visible where they are in intimate contact. Dusting the exterior of the polyester encapsulation very lightly with French talc or other fine powders prevents close contact between him and glazing and thus eliminate the patterns.

Some exhibit professionals may argue that encapsulations are aesthetically unpleasing or too reflective, but in many cases of smooth papers, textureless printing or script, an encapsulation is very difficult to detect. Reflections can be as readily a problem on frame or case glazing, as well as on the surface of glossy photographs. Reflection problems are chiefly a function of light source angle and placement and are best addressed by varying angle and placement of either the lights or the cases.

After Exhibition

When exhibitions come down, some or all of the display presentation can be

retained as improved housing when it is appropriate for storage. Very oversized drawings framed for exhibition are often best left framed for their protection in long-term storage, especially when they are too large to fit in available storage units. Care must be taken to protect framed items from long-term light exposure during storage and to store them securely so as to prevent their falling or breaking. Some items are displayed in so-called sink mats with special deep recesses to accommodate thick or fragile paperboards, undulating or cockled sheets, pendant seals, or other three-dimensional components.3 Such sink mats can be converted into protective storage housing by adding a top cover or lid. Special scaled custom-made housing for relative humidity control can be saved and reused for future exhibition of humidity-sensitive materials such as parchment.

Exhibition-related Hazards

Despite these possible benefits to a collection from exhibition, the inescapable truth remains that exhibition of art or documents on paper even under good conditions is less conducive to their long-term preservation than storage under good conditions. Exhibition requires light, generally requires exposing the item to large volumes of air (though inert gases can be substituted in special cases) and generally exposes the item to greater environmental fluctuations of

temperature and relative humidity. Although the word exhibition conjures up an image of items carefully resting, stationary in a hushed gallery space, in reality a great deal of movement and handling precedes and follows every exhibit. Items are handled during preliminary research, transported for photography and transferred within the building. The calm of the actual exhibition belies the rushed handling and installation crews who are working against an opening deadline. Exhibition can result in actual damage.