Creating Well-Sealed Frames and Display Packages
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A well-sealed frame or tightly-sealed display package can be used to create a microclimate which meets restrictive conservation criteria for environmentally sensitive, two-dimensional objects
What is a well-sealed frame or display package?
A well-sealed frame or display package is defined by the very low air exchange rate experienced by the enclosed object. A sealed frame or display package can be constructed to meet very restrictive conservation criteria for vulnerable or valuable objects and permits display of sensitive objects in situations that experience unacceptable environmental conditions. A well-designed unit can provide the following conservation benefits:
- Greatly reduces the ingress of dust, insects and atmospheric pollutants
- Block UV radiation by using filtered glazing material;
- Buffers against fluctuations in the ambient relative humidity;
- Slows a specific relative humidity to be maintained within the frame;
- Provides additional protection against water entry during a natural disaster, building system failure, or fire suppression
A sealed frame can be used for works of art on paper, documents, photographs, paintings, textiles, and three-dimensional objects that are relatively shallow. Sealed enclosures can be achieved in two ways: (1) insert a pre-sealed display package into a standard frame, or (2) seal the frame thus creating a microclimate. These methods are outlined in more detail below.
- 1. Major advantages of the well-sealed display package which is then set into a frame are:
- It facilitates rotation and substitution of objects by allowing a package
- Enclosing an object to be prepared in a conservation lab and then inserted into a frame.
- Any type of frame can be used, including metal strip frames and wooden frames.
- Only a minimum amount of alteration to the object's original frame is usually required; this is important when dealing with historic frames
- 2. Major advantages of a sealed frame include:
- This technique can be easier to implement than a sealed package, requiring only a few adjustments to standard practice;
- Advantage can be taken of thick, wooden frame walls to buffer against moisture migration;
- Careful attention to methods and material used can provide an excellent seal for very long periods of time
- Note: A particular concern for original or historic frames is that the technique sometimes requires significant alterations to a frame, such as resizing of the rabbet and sealing of the interior wood surfaces. A disadvantage can be a premature breakdown in the seal; sealed display packages are well suited to display periods of several years as opposed to decades.
How are sealed frames and display packages constructed?
The basic components of either system are the same. Working from the display side to the reverse, a sealed frame or package includes:
- Glazing: polyester film, rigid acrylic sheets or polycarbonate sheet, glass
- Spacer: mat board window, strips or bumpers such as polyethylene strips, conservation acceptable gasket
- Object: e.g. paper, photographs, paintings, textiles (attached to a support with appropriate method including hinging and stitching)
- Support board: mat board, painting stretcher including conservation acceptable rigid panel, stretched fabric
- Backing board: rigid panel that may be an excellent vapor barrier (aluminum) or incorporating a vapor barrier such as a metal foil laminate applied to the interior surface (materials such as corrugated acid-free board can also be used if the intent is to buffer, not control the environment inside the package)
- Seal: vapor barrier tape, gaskets; caulk sealants, sheets of metal foil or impermeable plastic
The primary difference between the two methods is the techniques used to seal the edge of the frame versus the edges of the package.
- Sealing a display package: The components of the display package are sealed along all four sides with a vapor barrier tape. Adhesion to the glazing and the backing board are absolutely critical. The tendency for the bond between the tape and the glazing to fail over time can be a problem in sealed display packages.
- Sealing a frame: Typically, a gasket is inserted between the rabbet edge of the frame and the glazing, or glaziers’ points and silicon caulk are used to securely seat the glazing to the frame and eliminate all air gaps between the two. The back plate can either be sealed through the use of a gasket, silicon caulk, or an over-layer of a vapor barrier sheet or tape.
Options to consider when designing either a sealed frame or a sealed display package include the following:
- Silica gel in a variety of containment forms, layers of hygroscopic mat board, and pollutant control papers or fabrics, can be included in the package. These materials are often located between the object support and the backing board.
- The use of hygroscopic materials inside the frame package can further stabilize the relative humidity.
- Only materials that meet stringent conservation criteria as low out-gassing, non-acidic, and chemically and physically stable can be used inside the sealed package or frame
Additional Bibliographic Resources
Laurent S.G. Sozzani, 1997. "An Economical Design for a Microclimate Vitrine for Paintings Using the Picture Frame as the Primary Housing" Journal of the American Institute for Conservation, 36:2: 95-107.
Daniel Vinod and Shin Maekawa, 1992. "The Moisture Buffering Capacity of Museum Cases" Material Research Society Symposium Proceedings, 267: 453-458.