- 1 Case Construction Materials
- 2 Design and Fabrication of Mounts
- 3 Exhibit Fabrication Standards
Case Construction Materials
Choosing Stable Materials
- Use nonhazardous materials close to objects, within case interiors, and in exhibit furniture. Select high-quality, conservation-appropriate materials; avoid materials known to offgas, become acidic, or lose their physical or chemical stability. Consult lists of materials that have been researched, talk with other museum professionals, and test proposed materials.
- Avoid adhesives when possible. If necessary within the object display area, use a conservation-appropriate adhesive with a successful track record in exhibits, such as one based on tested resins-acrylic, polyvinyl acetate, or certain high-temperature heat-activated adhesives.
- Review the composition of commercial interior finishes. Select nonhazardous paints and finishes, such as formulations based on 100% acrylic resin for wood or metal surfaces and powder coatings for metal surfaces.
- Allow sufficient curing time before installing objects. Approved caulk sealants and finishes require a minimum of three weeks to reduce emissions.
- Isolate objects from painted or varnished surfaces. Separate objects with a mount or a layer of inert paper, or other acceptable barrier, such as polyethylene, polyester sheeting or foil.
- Select and attach decorative fabrics with care. Check fabrics for dye stability and fastness; prewash and dry them before installation to preshrink and remove excess dyes and finishes. Use a mechanical attachment method or sew fabric to itself; archival-quality double-sided adhesive tape is useful for temporary exhibits.
Exhibit designers can choose from a wide range of materials for constructing exhibit cabinetry and finishing case interiors. From a preservation standpoint, however, it is crucial to use nonhazardous materials. Materials of unknown or questionable composition require research and testing. If problematic materials such as wood products are used within the display chamber, they must be isolated with a vapor-impermeable barrier. (see: Choosing Materials for Storage, Exhibition & Transport)
Wood, Plywood and Wood Composite Boards
Solid wood panels are sometimes used in exhibit construction, but wood emits corrosive vapors (acids and organic compounds) that can be harmful to many objects.
All wood products contain free acetic and formic acid, and more acid is generated over time. Elevated temperature and high humidity dramatically increase the release of gaseous vapors. Oak, in particular, is a poor conservation choice. Solid wood is expensive and has a low span-to-weight ratio-over long spans its strength is often insufficient and deflection occurs. Exhibit cases, shelving, and furniture are more often made from plywood, particle-board, and fiberboard which should be chosen carefully.
Plywood-both soft and hardwood-and wood particle- boards are made with one of three adhesive formulations: urea-formaldehyde, melamine-formaldehyde, and phenol-formaldehyde. These adhesives or their additives offgas chemicals that have caused damage to a wide range of collections. They
- cause proteins and cellulose to crosslink;
- alter the color of some pigments;
- corrode metals, especially lead alloys; and
- promote the formation of crystals on glass.
In most instances it will be necessary to specify products made with phenol-formaldehyde, the most stable of the three common adhesive types, when plywood or wood particleboard is used. Phenol-formaldehyde products are usually sold as exterior grade. A polyvinyl acetate or PVA adhesive is used with hardwood plywoods. This type of adhesive system is often preferable due to the fact that there is no harmful emission rate. These wood products can be expensive and difficult to locate.
Over the last decade wood composite boards such as particle and fiber board were often used in the construction of museum exhibits due to their affordability and dimensional stability. Most of these boards however, give off formaldehyde emissions; therefore, it is recommended that standard particleboard and fiberboard not be used in exhibit case construction. There are exceptions, however, because some manufacturers make specialized boards which do not utilize the more hazardous resins. The quality and characteristics of any Medium Density Fiberboard (MDF) or Medium-density overlay board (MDO) must be carefully considered.
Many different glues and adhesive systems have been used in exhibit assembly. Most adhesives emit large quantities of solvents and unreacted monomer vapors during their drying or setting phase. Even after this initial period, offgassing can continue indefinitely.
Some of the most damaging adhesives fall into the categories of contact and pressure-sensitive adhesives. Rubber-based adhesives, either vulcanized or synthetic, age poorly due to their sulfur and chloride content. Two- part adhesive systems, such as epoxy and polyester types, also have a poor track record for stability. Traditional hide glues can be problematic due to their sulfur content. Less harmful adhesives include acrylic resins, polyvinyl acetate, and certain high-temperature heat-activated glues.
Careful design can reduce the need for adhesives and prevent adhesive vapors from entering the display chamber of an exhibit case. Fabrics can be wrapped around elements and secured with rustproof staples or pins or other mechanical fastenings instead of adhesives. Other attachment methods include hand stitching and archival-quality double-sided tape. When adhesives must be used inside the display chamber, seal exposed or problematic joints with a conservation-safe caulk, or apply an effective barrier laminate or foil over seams.
Paints, Varnishes and Caulks
Paint systems, varnishes and caulks contain a variety of chemicals, including ammonia, formaldehyde, sulfur, organic acids, and solvents. Alkyd or oil-based paints are known to offgas for long periods. Select nonhazardous paints and finishes with little or no volatile organic compounds emission (VOC's) such as formulations based on 100% acrylic latex for wood or metal surfaces and powder coatings for metal surfaces. Several major paint manufacturers now provide products which are labeled "zero" VOC.
Because latex paints become tacky in high-humidity situations, always isolate objects from painted surfaces in the display chamber with a barrier layer of inert paper, foil, or polyethylene or polyester sheeting, or elevate the object with a mount. Before installing objects, allow the finishes to cure. Nonhazardous paints, varnishes and caulks require a minimum of three weeks of curing time to reduce emissions. Wood products used within the display chamber must be sealed before being painted.
Fabrics and Cushioning Foams
Designers achieve different decorative objectives by using fabrics to line walls, pedestals, and case interiors. A systematic review of these materials and their installation techniques is extremely important to avoid introducing a source of pollutants. The fiber composition, dyes, and any finishes applied to a textile should be assessed for potential contamination of the exhibit environment.
Wool fabrics (including felts containing wool) emit volatile sulfur compounds that are damaging to silver metal, photographs and other materials. Pure cotton, linen, silk, and polyester fabrics are generally suitable, although any fabric may have been treated with an unacceptable finish or dye. For example, permanent-press cotton is often treated with formaldehyde. Mothproofing agents and anti-static treatments may contain formic and acetic acid. Some of these finishes are water-soluble, therefore it is recommended to wash fabric in hot water before use.
Dyes used in decorative fabrics can transfer to display objects during periods of high humidity and from accidental wetting. Test textiles proposed for use for water-fastness by blotting wet sample swatches on white toweling-use at least 2 samples and soak one for 1 minute and the second for 5 minutes in water). If the dye is not water-fast, it may be possible to make the fabric acceptable for use by washing it repeatedly until the water runs clear.
Carpet has also been identified as a source of unsafe volatile chemicals. While carpet is seldom used inside a case, the quantity used in an exhibit space makes informed decision making important. A cotton fiber with a short nap is ideal; if it is unavailable, choose a synthetic fiber. Avoid rubber-based backings, which are often integrated into the base of the carpet fiber. Some conservation-safe synthetic felts have been identified for use as exhibit mount lining fabrics.
Hook and loop-type fabrics made of pure nylon are acceptable, but those with a thin, foam backing containing polyurethane should not be used.
Foams are often used to construct mounts or textile display forms. They are also useful as a cushioning material for mounts. Select foams based on their stability. Polyethylene foams that are crosslinked with radiation or foamed with inert gas are the most stable types available.
Using Less Stable Materials
- Use the least hazardous materials, and isolate objects from them. When problematic materials cannot be avoided, select low-acid, low-offgassing, formaldehyde-free products.
- Seal or isolate all wood products. Apply barrier coatings, foils, or laminates to isolate raw wood and wood- composite surfaces that are close to objects, especially within exhibit cases.
- Aerate the case. After applying coatings and sealants, allow enough time for curing before installing objects. A minimum of three weeks is recommended, with case doors open and vitrine bonnets removed.
- Isolate objects from problematic surfaces. Wood products, even when coated, must not come into direct contact with objects. Physically isolate objects with safe fabric coverings, acid-free paper or board, foil, or an acceptable plastic barrier such as polyester or polyethylene sheeting.
- Incorporate a pollutant absorber or scavenger. When the possibility exists for even low level emissions within a sealed case introduce a gaseous pollutant absorber.
When less-than-ideal materials must be used for practical reasons, such as cost or availability, or when collection objects are particularly sensitive to offgassing, seal all exposed, interior surfaces. Solid barrier layers and specialized coating systems can be used to seal the questionable material and reduce the amount of out- gassing entering the display chamber. As an additional measure of protection a pollutant absorber can be introduced in these cases.
From a conservation standpoint, wood and wood products are not ideal materials for exhibit construction, particularly for well-sealed exhibit cases. When using wood within a display, always seal the surface to inhibit undesirable emissions. Common barrier materials include metal foils, plastic or composite films, plastic or resin laminates, and specialized coating systems. Not all of these barriers (rigid sheet or coatings) can be painted. All effective barriers, however, must have the following characteristics:
- be effective for the emissions targeted
- release no harmful volatile emissions themselves
- perform consistently, even under atmospheric moisture change and dimensional changes in the substrate
It must be understood that for coatings to operate effectively as barriers the manufacturer's application instructions and thickness requirements must be followed.
Aerating the Case and Isolating Objects
The initial offgassing from exhibit production materials will be very high as the adhesives and paints cure and the solvents evaporate. Research shows that many polymers continue to offgas over time, only at a slower rate. After three weeks, however, there is a dramatic decrease in emission for many commonly used paints, finishes, and caulking sealants.
Build time into the schedule for aerating the case and allowing the highest gas concentrations to dissipate. A minimum of three weeks is needed between completion of case construction and object installation. During that time, open the case doors and remove the vitrine bonnets. When large quantities of less stable materials are used, or when the objects are particularly vulnerable to chemical pollutants, provide increased ventilation during curing.
Only inert materials should be in direct contact with objects. To prevent deterioration from transfer of acids and other chemical reagents, isolate objects from unknown and reactive materials. Dyed, painted, and abrasive surfaces can also cause damage. To protect an object, suspend it from a mount or place an inert layer of linen, cotton, or polyester fabric, polyester or polyethylene film, acid-free paper, or paperboard between the object and the surface.
Design and Fabrication of Mounts
- Design and fabricate mounts for object installation ahead of time. Use a qualified mounting specialist who has conservation training; some objects require the direct involvement of a conservator. How an object will be displayed and what type of mount is required are early design decisions.
- Protect the integrity of the object. No object can be physically altered or dismantled to accommodate placement or mounting in the exhibit. Use mechanical designs to lock mounts in place.
- Support the entire object. The object's center of gravity or originally intended attitude should be considered when designing a mount. Support provided by the mount must prevent physical stress or unbalanced weight distribution.
- Provide adequate support for flexible objects. Create custom-padded mounts for organic materials that support the structure over its entire contour. Textiles, papers, organic materials, and other susceptible objects should not be creased or folded, nor should heavy objects be placed directly on top of them.
- Support all parts independently. Fragile objects, including textiles, should be supported over as large an area as practical. Attached parts, such as straps, may require independent support.
- Stabilize objects from vibration. The mount design should reduce vibration when a case is bumped. A cushioning material is often required. The mount should fit the object evenly to prevent abrasion.
- Ensure the security of framed works. Attach them to the wall with appropriate hardware such as 'D' hooks and braided metal wire. Anchor the wall fastener firmly to the wall and be sure that it can support the weight of the framed object.
For more information visit the AIC wiki pages on Mountmaking
The production phase of the exhibit process is a critical step in the realization of a preservation-responsible exhibit. During this phase, multiple levels of conservation are implemented. The exhibit conservator is part of the team that inspects and tests the exhibit cases, lighting systems, and object mounts. After construction and testing are complete, the exhibit space can be cleaned of debris for object installation.
Careful mount making and object installation are time-consuming endeavors that must be accommodated in the installation schedule and exhibit budget. Care of the objects continues even after the exhibit opens to the public. A maintenance plan must be established and carried out.
The exhibit team must make decisions about object presentation early in the design phase. Whether to display objects in an open format or within exhibit cases is often the single most influential choice for preservation. Decisions about mounts, which should be designed well ahead of installation, are also made in the early design phases and often require considerable participation from the conservator. The curator, conservator, and other relevant team members should discuss mounting options with the designer, preparator, and installer. There may not be enough time to mount all objects safely, dictating different object selections or the use of more generic mounting approaches, such as shelves. Discussions should establish the acceptable viewing angle and the geometry of the object's appearance. Other questions affect preservation, including:
- Should objects be displayed in a vertical or a shelf-supported position?
- Will mounting systems be suspended from the ceiling or attached to the walls or floor?
- How will textiles be mounted?
- Will all paper-based images and paintings be framed?
It is particularly important that the conservator be involved in decisions about mounting of vulnerable and problematic objects. Improperly designed or constructed mounts can scratch, bend, discolor, corrode, or otherwise damage an object. A conservation-appropriate mount, on the other hand, will strive to:
- present the object in a desired orientation with the least stress on materials;
- support the object over its entire length, with separate support for any attachments;
- cushion the object with safe materials that buffer the adverse effects of vibration; and
- stabilize the position of an object, especially if its shape is irregular.
Types of Mounts
Exhibit mounts generally fall into two categories, reflecting their complexity and the skills required for their fabrication: generic and custom mounts. Generic mounts can be purchased, or they can be made or adapted by staff members who have good manual skills and a basic knowledge of object handling. Because a generic mount does not suspend an object, it can be installed using common sense. A conservator rarely needs to be consulted. Generic mounts usually have the following features:
- Require little object handling and fitting
- Require only rough measurements.
- Usually require no consultation with a conservator
- If produced in-house, require some skills of a mount fabricator
- Usually present the object in a simple, planar orientation
- Can be purchased as stock items.
Examples of generic mounts include book cradles, stands for paper objects, boxes or pedestals for three-dimensional objects, ring stands for pottery, and pressure mounts for papers. Generic mounts may require some adjustment or additional cushioning material to provide even support for the object. Book cradles, for example, must be sized for the volume; padding can be contoured to the spine and covers.
Custom mounts always require technical skill and a knowledge of objects. These mounts are often constructed by the exhibit preparator or mount maker in consultation with a conservator. Constructing a custom mount may be part of the conservation treatment for a particularly fragile object. Custom mounts have these characteristics:
- Require object handling, individual measurement, and fitting
- Usually require consultation with a conservator
- Can be designed and fabricated by a highly skilled mounting specialist
- Present the object in a well-supported, suspended, or otherwise complex orientation
Custom mounts are generally made from rigid acrylic, brass rod and strap, high-density polyethylene foam, paper products, or textiles. Examples of custom mount types include:
- Metal rod 'T' mounts
- Metal rod 'spider' mounts
- Drop mounts or rod and sleeves
- Pin mounts
- Straps or clips
- Mannequins or partial three-dimensional forms
There are many different preservation-responsible methods to support and mount any object. Discussing options with a conservator may lead to a new approach. Several conservation issues, common to all mounts, must be resolved:
- Size of the mount
- Method of holding the object
- Method of attachment to the exhibit furniture
- Materials used to construct the mount
- Finishing of the mount
A properly mounted object is well-supported and protected from slippage, jarring, and movement from air currents, vibration, and visitor activity. Support over the entire length, width, or diameter of an object often requires that the mount be padded to the object's contour. Appropriate cushioning materials include polyethylene foam, polyester felt, and fabric-covered polyester batting. Cushioning can be attached to the mount with archival-quality double-sided tape, staples, pins, or heat-activated adhesive, or it can be sewn into place.
The cushioning material and technique must always support the object without abrasion or stress. Support is especially crucial for objects that are pliable or flexible by nature or due to advanced deterioration. Mount design must anticipate the tendency for organic materials to droop, sag, or experience dimensional changes. Textiles and other fiber-based materials are susceptible to creasing, tearing, and deformation. Original clamps, hooks, strings, or straps already attached to objects should not be used for support or to bear the weight of the object.
The system for attaching a mount to the exhibit hardware and to the furniture must be based on a mechanical design. It is never acceptable to alter, dismantle, or reconfigure an object to fit a mount. Likewise, the mount must not be fastened around an object so that removing it is difficult. Straps or brackets should fit snugly, but not too tightly, so that objects are supported but not distorted or scratched. Cradles should gently support objects, not compress them.
Never glue an object to a mount or drill into it for mounting. It is rarely acceptable to attach an object directly to a wall or ceiling; attach the object directly only in unique situations where the size or complexity of the object allows no other means of support. Conservators frequently debate the wisdom of introducing conservation-grade wax to secure nonporous objects to exhibit surfaces. For certain objects in locations where there is a real threat of earthquakes, it can be an acceptable practice, but there is usually a less hazardous alternative.
Where possible, the mount should be secured in place within the exhibit before the object is positioned. A 'drop mount' simplifies object retrieval because one section fits over the object, which is then dropped into a prefabricated fastening device.
Material Selection and Fabrication
Object mounts, like other parts of the exhibit, must be made of the most stable materials possible. Rigid acrylic or polycarbonate, brass rod and straps, and paperboards are common mount materials. Remove sharp edges from all surfaces close to the objects. This step may require polishing plastic mounts or filing and polishing brass mounts. Metal mounts must always be covered with an inert fabric or foam or coated with a barrier such as an acrylic resin or silicon rubber.
A cushioning material may also be used to provide a smooth contact surface, and it may be required to pad the object. Use only high-quality padding and cushioning materials, such as polyethylene foam, polyester batting and felted material, 100% cotton fabrics, and acid-free buffered tissue paper.
Secure framed works to the wall with appropriate hardware such as 'D' hooks and braided metal wire. Anchor the wall fastener securely to the wall and be sure that it can support the weight of the framed object. Two independent hangers are recommended for frames and framed objects.
Mannequins and forms that support garments must be made from inert materials, such as polyester batting or polyethylene foam. As an alternative, use cotton fabric to buffer the textile from direct contact with questionable material, such as sealed wood and certain foams. It is imperative that mannequins and support forms are sized appropriately to the textiles. In older or degraded pieces, the actual woven fabric, as well as the seams, may split under pressure. Muslin linings and backing are often needed to reinforce and protect garments and hanging textiles. These materials should be applied by a qualified conservator.
Exhibit Fabrication Standards
The following standards are suggested for developing best practices for exhibitions within an institution. click on the Standards below to view the associated guidelines that expand on the topic.
Fabrication of exhibit structures and the exhibit environment must conform to the design documents and follow all conservation specifications
Protective measures must ensure object safety during fabrication
OR: Objects must not be exposed to the dust and physical risks inherent in fabrication
Any modifications (such as structural changes or technical controls) that have been planned in order to fulfill the object Conservation Requirements must be made as specified
OR: Planned modifications must be made to the Exhibit Space to fulfill the Conservation Requirements
The recommended object conservation treatments must be performed to stablilize the objects and prepare them for going on safe exhibit.
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Pages in category "Exhibit Fabrication"
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