Research specialist Anna Laganà testing materials and methods to repair damaged unsaturated polyester objects. Photo: Anna Flavin.

Transparent plastics, such as unsaturated polyester (UP), poly (methyl methacrylate) (PMMA), polystyrene (PS) and cellulose esters, have been extremely popular with artists and designers due to their versatility and optical properties. Since their introduction, they have been extensively used to make sculptures and objects and used as paint support. Even photographers have begun including these plastics in the production of contemporary photographs; since mid-1980s, clear poly(methyl methacrylate) sheets have been used to face-mount photographs.

For conservators, objects made of transparent plastics entail a whole new set of challenges. Their smooth and pristine surfaces are easily harmed and their transparency tolerates very little damage. Surface damages frequently occurs during handling or transportation and can be extremely disfiguring for these works of art—especially on face-mounted photographs where damage appears directly in front of the image.

Selecting suitable conservation materials and methods to repair any mechanical damage on transparent plastics—such as scratches, abrasions, cracks, chips, and broken parts—is difficult. Many factors must be considered. For example, adhesives that contain solvents or produce heat during curing can damage plastics or cause alterations such as stress crazing. Repair materials often have compositions similar to the original plastics, making reversibility a challenge, and for this reason, their behavior upon aging is an especially crucial factor to consider. Moreover, making invisible repairs is as difficult for transparent plastic objects as it is for broken glass.

Because of their low tolerance for damage and the difficulty of achieving inconspicuous local repairs, these objects often undergo invasive treatments, such as polishing or sanding, (often entailing the removal of significant quantities of original material) and, in extreme cases, total re-fabrication. Therefore, an important objective of the Preservation of Plastics project is to investigate suitable and less-invasive repair options for these types of objects in order to provide conservators a wider range of repair options than are currently available.

This component specifically explores:

fill materials and methods to repair deep scratches and chips without modifying the original surface to provide less-invasive solutions for these type of objects;

materials and methods for loss compensation (including the potential to use 3D technologies);

Unsaturated polyester resin mock-ups by Eric Johnson used to investigate repair materials and methods for scratches, chips, and losses on polished polyester resin sculptures. Photo: Anna Flavin.

adhesives and joining techniques to repair broken parts.

Fill materials and adhesives ability to improve the visual appearance of damage is tested on damaged test-samples and mock-ups and assessed with naked eye observations, as well as with optical microscopy; their suitability and stability is evaluated in GCI laboratories using a wide range of instruments and techniques.

Materials and methods providing the best results are used by the project team to treat damages on representative case studies selected from museum collections.

To this end, the project has investigated:

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Page updated: November 2017