The display of objects, either as a large scale exhibition or a single showcase, is still a form of storage, albeit one that is visible and accessible to the public. In addition to the aesthetic presentation of objects in exhibitions, objects must also be protected against the usual agents of deterioration.
Objects can be exhibited on either open display or closed display within a showcase or cabinet. Open display is often the domain of larger objects while smaller objects are well suited to exhibition in a custom made showcases. Regardless of the design of the exhibition all objects will require a stable environment for the duration of their exhibition.
Objects are often designed to be on open display as audiences respond well to fewer physical and intellectual barriers between them and objects of interest. As there is no glass to spoil the view of the object, audiences can interact with objects more closely and the gallery atmosphere often appears more relaxed and open. Open display also provides a means of displaying large objects that would otherwise never be seen by the public as the costs and means needed to construct and transport custom sized showcases are extremely high.
Some considerations for objects on open display include:
- Temperature and relative humidity levels in the gallery space need to be less prone to fluctuations and may require adjustment to meet the requirements of the objects on display since they will not be buffered by a showcase;
- Exclude direct daylight from entering the gallery and use an appropriate and flexible lighting system that caters for the light and UV sensitivities of the objects on open display;
- When selecting materials from which to construct internal walls or furnishings (such as plinths), ensure that conservation grade materials are used (see the chapter Preventive Conservation: Agents of Decay);
- Choose paints for the building and internal structures (including plinths) that have minimal volatile organic components. Allow approximately 4 weeks for the paint to off gas before installing objects;
- Consider the security of the gallery space. Are there visible security guards or attendants present? and
- Consider the air filtration system and possible pollutant sources, including visitors who will be in close proximity to the objects on open display.
- Objects on open display are generally more vulnerable to damage through inappropriate handling by the general public. As such, keep objects out of touching distance (generally an arm’s length or a minimum of 800 mm) by the use of either psychological barriers such as low level or sloping plinths that prevent the public from getting too close or physical barriers such as roped off areas, acrylic or glass barrier screens;
- Consider the stability of the object and if it can withstand the vibrations that may occur around it with people walking or running near it;
- Use a barrier layer such as Mylar™ under an object if it is placed directly on a painted surface to prevent the transfer of paint to the object. Foam such as high density Ethafoam™ PE30 may also be placed underneath objects to cushion their bases from hard floor surfaces;
- Consider the security of the object. What systems are in place to prevent theft? Are there pins attaching the object to the plinth or is it heavy and large enough so that it cannot be removed without someone noticing?
- Objects on open display require more regular maintenance and cleaning than objects in showcases as they are more exposed to the dust and pollution that is inside the gallery space. These objects are also more exposed to insect activity.
Closed Display - Objects in Showcases.
Showcases work quite effectively in grouping objects together and by protecting delicate, small and precious objects. Some cultural materials including certain types of rubber, plastics, wool and wood emit damaging gases that can accelerate the deterioration of other objects if they are confined in the same microenvironment within a showcase. Separate these materials and take appropriate steps to minimise the impact of pollutants generated by objects themselves (see the chapter Preventive Conservation: Agents of Decay). Showcases should have the minimum of visible structure so that there is the least possible distraction to viewing the objects. When sourcing or designing a showcase consider the following:
- type of construction materials;
- props and textiles for ‘dressing’ the case;
- glass or acrylic for panels and lids;
- stability and vibration;
- environmental control;
- pest monitoring;
- case access;
- lighting; and
- mounting and supporting objects;
As microenvironments develop within display cases choose materials for their construction that are compatible with the objects that are to be displayed. Inert, inherently stable materials like glass, metals and some plastics including acrylics (like Perspex™ or Plexiglass™), polycarbonates and polyesters are all suitable. Many organic materials (resins, plastics, coatings, wood, adhesives and wool) release damaging gases including formaldehyde, acetic acid and sulphur compounds. Avoid incorporating these materials in showcases either as construction materials or as display props.
Do not use medium density fibreboard (MDF) or zero-formaldehyde MDF for display cases as they are not chemically stable. Instead use exterior grade Australian hoop pine plywood. Use either aluminium foil laminates such as Marvelseal® 360 or Moistop 622 Barrier Foil (Hook 2005) or a water-based polyurethane to seal the plywood to prevent organic pollutants from the wood and adhesives from being released into the display case environment. While the foil laminates are more expensive than polyurethane they are more effective at sealing wood. If using the water-based polyurethane, apply at least two coats of the sealant with a light sanding in between layers and allow 4 weeks for the fumes to sufficiently off-gas before enclosing objects in the space. Regardless of the sealant used, it is critical to seal all exposed surfaces, especially the edges and ends.
Display Props and Textiles
Having already established that the objects going into a display are pest free, it is most important that any props augmenting a display, particularly organic ones, are pest-free prior to being installed. Observe and treat all organic props to ensure that no pests are introduced into display cases.
Wash props like sand or stones before using them. Drying in an oven after washing will ensure that these props are also insect-free.
Wash all textiles that will be used as background display materials to remove finishes such as pest proofing and flame retardant agents. Do not use wool, silk, some rubbers and some treated leather products in display cases as they degrade to produce sulphides which will attack any metals in the cases. Test textiles for colour fastness especially if they will be in direct contact with objects (see the chapter Textiles).
Glass or Acrylic Panels and Lids
Glass and acrylic materials each have their own particular advantages and disadvantages when used in exhibition showcases. Glass provides a better seal when creating microenvironments but is heavy and expensive. Glass has a long life, can be used for larger size cases, allows for better hinge choices and with laminated glass, offers very good security for objects on display. Laminated low-iron glass is recommended as it is stronger, has a lower light absorption rate than clear glass and lower reflective properties.
Acrylics such as Perspex™ or Plexiglass™ are cheaper, lighter, do not break as easily as most glass, are easier to bond and easier to replace in an emergency. These are significant advantages if used for travelling showcases. Disadvantages of acrylic materials are their less scratch resistant surface, vulnerability to vandalism, tendency to craze with constant cleaning, limited opening techniques (acrylics and hinges don’t work very well together) and size limitations as acrylics do not work very well for large cases.
As a general guide, acrylics are recommended if short-term displays of up to 2 years are planned. If displays are planned for longer periods then glass is preferred. Do not use tempered glass in display cases as their shattering properties could lead to objects being showered with thousands of small glass fragments!
All glazing edges must be polished or fitted with edge protection. Glazing joins should be mitred and glued with an appropriate adhesive.
Stability and Vibration
Vibration and movement from external sources can cause damage to objects inside a showcase. Cases must therefore be structurally stable and secured to prevent their movement and the movement of the objects inside the cases. Ensure the stability of objects in a case and their ability to withstand vibrations that may occur around the case with people walking or running in the vicinity. Secure showcases against:
- the transmission of vibrations from surrounding floor areas to the interior of the showcases;
- any vibration associated with opening the case and while open; and
- any vibration or movement from drawers that may be part of either moveable display units or used to incorporate buffering/pollutant absorbing material in the display cases.
Well cushioned stoppers will reduce the vibration and minimise any physical damage to objects. Objects displayed in drawers need to be robust enough to withstand the movement and be supported on appropriate props that minimise possible damage.
A comprehensive table of environmental requirements for cultural materials is provided elsewhere (Appendix 2). This appendix lists appropriate temperatures, relative humidity levels, maximum light and UV levels, maximum display periods per year, susceptibility to insect/mould attack and other conservation considerations. Some materials require specific environments that are free of oxygen, moisture or sulphur. Strategies for controlling environments to create favourable conditions that enhance long-term preservation are also provided elsewhere (see the chapter Preventive Conservation: Agents of Decay)
A well designed showcase can create a favourable internal microenvironment by using materials that buffer against environmental extremes and fluctuations and can also minimise problems associated with biological pests and airborne pollutants. Some methods by which these levels of control may be achieved are discussed below.
Seal display cases to exclude dust, minimise the ingress of pollutants and insects and form a buffer to ambient temperature and relative humidity changes. Such a sealing system should not be completely airtight or hermetically sealed however as it is necessary to allow one air exchange per day to avoid the build-up of potentially damaging fumes. Neutral-cure extruded silicon seals (either compression or adhesive gaskets) are suitable seals for display cases.
Relative Humidity Buffers
Buffering agents such as acid-free papers and fabrics can be incorporated into displays and as such will absorb moisture in a display case where fragile, humidity-sensitive materials are present. A facility drawer built inside a showcase will enable the use of silica gel in a cassette or Art-Sorb® sheets to similarly control relative humidity levels inside showcases.
Corrosion Inhibitors and Pollutant Control
A facility drawer in a showcase will also allow for the use of corrosion inhibitors (vapour phase inhibitors) where organic materials are displayed in proximity to metals that require low RH (less than 40%). Corrosion inhibitors will protect the metals on display and are usually active for 12 months. Activated carbon cloth or Microchamber™ papers and boards could also be placed in the facility drawer (or even as part of the display design) to reduce the effects of organic pollutants on susceptible objects such as lead.
Marvelseal® 360 is an aluminium based nylon and polyethylene moisture barrier film that will resist the passage of moisture and pollutants. It is an ideal barrier for the lining of wooden display cases, shelves and for lining transport crates.
All of the above methods require regular maintenance and monitoring in order to remain effective in controlling the environment within the showcase.
A well sealed showcase will also limit insect activity inside a showcase. Do not use insect repellents or pesticides inside display cases as they create toxic microenvironments. Instead treat any insect-infested objects before placing them in cases and if necessary apply residual pesticides to skirting boards and to external parts of display cases and surrounding areas. Use sticky insect traps to monitor objects and displays, especially dioramas, which are susceptible to insect attack (see the chapter Mould and Insect Attack in Collections).
Access is an important part of display case design. Limit the weight of doors and choose door equipment that is precision engineered for ease of use, maintenance and safe operation by one person. The doors of a display case must allow at least 60 – 90 % access to the display area without affecting the structural integrity of the case so that objects can be moved safely and maintenance carried out.
Most importantly, at no time should an object be put at risk through the opening movement of the door. In a sliding door system, the moving glass panel must slide in front of the one in the fixed position.
Ensure that all showcases have locks or security screws installed to prevent the theft of valuable items. Install locks to the top and bottom rails of large standing showcases and to two sides of showcases that have four visible sides. When planning a large exhibition or permanent gallery, consider having all the showcases keyed to the same locking system to reduce the number of keys required. Ensure that there are at least two sets of keys to the showcases and that they reside somewhere that is accessible in disaster response situations.
Museums must provide adequate lighting for viewing displays while at the same time reducing the risk of fading and damage caused by exposure to light and UV radiation. While light sources, lighting techniques and associated recommendations are described elsewhere (see the chapter Preventive Conservation: Agents of Decay), it is worthwhile emphasizing the following points:
- do not incorporate lighting systems inside display cases as the heat generated can cause a multitude of problems;
- use lights with low UV levels and high (> 90) colour rendering indices so that the true colours of objects can be observed;
- use lighting arrangements that allow for easy maintenance and control of light levels; and
- set light levels in a case to cater for the most light-sensitive object in the display.
Mounting and Supporting Objects
In order to accommodate a number of objects and to make a display more dynamic, objects need to be mounted in some way. Some objects may also require support because they are fragile, inherently weak or deteriorated, are at risk of damage when handled or require arranging or displaying in a certain way so that the interpretation of the object is clear. While it is acknowledged that compromises may be required between the conservation requirements of adequate support and the aesthetically pleasing look of a display, the safety and long-term preservation of an object must always be the number one priority.
Although preparing and supporting objects for display are specialised tasks, some methods and materials are described below.
All materials used to mount objects in a display should be inert and of archival quality. In addition to the materials described previously (see the chapter Preventive Conservation; Agents of Decay), acrylic rod, stainless steel rod covered with silicon tubing, fishing line and magnets are acceptable for use for display mounts. As specified countless times, ensure that all wooden parts including display props, plinths and similar object are suitably sealed, either using a water-based polyurethane or Marvelseal® 360 barrier foil.
Do not use Blu-tac, sticky tapes, plasticine and similar materials to mount objects for display. Over time the adhesion will fail and the oil or adhesive will migrate into porous material and leave an irreversible stain on the object. Likewise thumb tacks and nails should never be used as a mounting media in direct contact with objects as they cause permanent damage by leaving holes in objects.
Use physical barriers to avoid having objects in direct contact with display case materials like wooden or painted surfaces. This minimises the risk of damage to the object by the transfer of potentially damaging chemicals. Mylar™ (cut to shape) is a useful product to place as a barrier between an object and a display case surface. Also consider using an acrylic plinth or support to raise an object from a risky surface.
Other considerations include ensuring that:
- all shelves or plinths are strong enough to support the weight of the objects;
- there is sufficient padding at contact points with the object without compromising the object’s stability;
- the mount does not have sharp edges and is non-abrasive;
- display materials are colourfast, economical and durable; and
- display furniture is as unobtrusive as possible.
Internal supports may be required for objects that are vulnerable to collapse over time, as well as for non-rigid objects like some leather objects and textiles. Bonnets, hats and baskets for example, will usually require internal covered structures to support their shape. The support could be a shaped Dacron™ filled cushion or a shaped and covered structure such as Ethafoam™ (Figure 16). Loose wadding such as Dacron™ is unsuitable for use as a support as pressure is put on the inside of the object as opposed to the cushion cover and loose fibres may attach to the inner surface of the object.
Costumes and garments should be supported on well-fitting mannequins where appropriate (see the chapter Textiles).
An object may require an external support to assist in holding it in a stable position or in a position that is necessary for its proper interpretation. A canvas diving suit for example could not be displayed in a vertical position without external support as it is not capable of supporting its own weight. In such cases locate suspension points in the strongest areas of the object.
Books, if displayed open, also require support. Use custom-made stands to support the structure of the book at about 150° so that the spine is not stressed over time (see the chapter Paper and Books).
Larger textiles that are hung for display require a supportive and strong hanging system while smaller textiles might require mounting on a padded board for support (see the chapter Textiles). Hanging or suspending objects can be fraught with potential problems and the risk of damage to an object is high. Contact a conservator for advice if considering this display option.
Pre and Post Display Condition Reports
Examine and document all objects before they are displayed and again at the end of their exhibition period. Written descriptions, photographs and sketches may all form part of the condition report documentation. By doing this it will be possible to determine if objects have suffered any damage while on display. If objects have been damaged while on display take steps to rectify the situation.
Display Criteria Checklist:
- Are the materials within the display area inert?
- Have all the environmental issues been addressed within the display environment?
- Have condition reports been done?
- Are the objects adequately supported? and
- Have all props been properly quarantined?