Conservation and restoration of objects made from plastics is work dedicated to the conservation of objects of historical and personal value made from plastics. When applied to cultural heritage, this activity is generally undertaken by a conservator-restorer.
Within museum collections, there are a variety of artworks and artifacts that are composed of organic plastic materials, either synthetic or semi-synthetic; these were created for a range of uses from artistic, to technical, to domestic use. Plastics have become an integral component of life, and many plastic artifacts have become cultural icons or objects worth preserving for the future. Although relatively new materials for museum collections, having originated in the 19th century, plastics are deteriorating at an alarming rate. This risks the loss not only of the objects themselves, but other nearby materials may also be degraded by outgassing or reactions with other released chemicals. [1] [2]
Identification of plastic components of a collection is extremely important, because some plastics may release a harmful toxin or gas that can damage nearby objects. A preservation plan can be established to slow down the effects and protect a collection. [3] [4]
Plastics are identified by various methods, including trade name, trademark, or patent number. Depending on the manufacturer, different chemical formulas and materials may have been used to produce the plastic over the years. [1] A recycling code may be present, giving general information about the material composition. Plastic composites or proprietary blends can be more difficult to identify.
If there are no markings to identify the type of plastic used, it may still be identified by using various types of spectroscopic technology such as optical spectrometer, Raman mid-infrared spectroscopy, [4] and near-infrared spectroscopy, along with mass spectrometry. [3] Other forms of identification include elemental analysis or thermal analysis to decipher the composition of plastics. [3]
The Museum of Design in Plastics (MoDiP), has created a guide to plastic objects that includes the manufacturing dates and manufacturing processes, along with its typical characteristics such as feel and smell. [5] If an object in a collection has characteristics that differ from what is expected, it is possible that the piece has begun to deteriorate.
In 2022, the Getty Conservation Institute published a book on the properties of commonly-used plastics and elastomers, including 56 "fact sheets" summarizing important characteristics of the materials, and methods of identification. [6]
The list below is of chemical compositions that make up common plastics found in museum collections. These are some plastics that may degrade, but are not seriously harmful to nearby objects:
The following are "malignant" plastic materials that will age rapidly if left untreated, and which have a higher risk of off-gassing or releasing toxic materials that can damage surrounding objects: [3]
Environmental concerns have driven recent changes in plastic manufacturing towards biodegradable plastics, [10] with a potentially negative effect upon the long-term stability of such materials within museum collections. [11] [8]
A difficult aspect of plastic deterioration is that one cannot see what types of chemical reactions are occurring in the interior of an object, or easily identify the makeup of proprietary plastic composites. Many plastics will give off a distinct odor, ooze liquids, or will begin to shrink or crack in some way as they age. [12] Although deterioration cannot always be stopped, it is important to know the causes and be able to mitigate or slow damage.
The causes of deterioration regarding plastics can be linked to age, chemical composition, storage, and improper handling of the objects:
Understanding the different types of plastic chemical degradation helps in planning specific measures to protect plastic artifacts. Listed below are types of chemical reactions that accelerate the deterioration of the polymer's structure:
| Plastic | UV radiation and excess light (photolysis, photo-oxidation) | Moisture (high relative humidity) and moisture fluctuations (hydrolysis, swelling, shrinkage) | Pollutants | Effects on other nearby materials (stains, corrosion, stickiness, gases) |
|---|---|---|---|---|
| Acrylics | resistant | resistant | dissolved, swelled, stress, cracking | none |
| Casein-formaldehyde, protein derivatives | formaldehyde gas, cracking due to swelling/shrinking, moldy appearance, brittle when dry | swell by water, resistant to organics | formaldehyde, hydrogen sulfide, other sulfur-containing gases | |
| Cellulose acetate | yellowed, brittle | hydrolysis produces acetic acid oily plasticized liquids. White powder residue may also be visible [15] | dissolved swelled | acetic acid gas, oily plasticizer and degradation products on surface |
| Cellulose nitrate | yellowed, brittle | hydrolysis produces acidic and oxidizing nitrogen oxide gases | dissolved, swelled | acidic and oxidizing nitrogen oxide gases, plasticizer, and degradation products on surface; material is explosively flammable |
| Nylon (polyamide) | yellowed, brittle | potential hydrolysis at extreme conditions | softened, swelled | none |
| Phenolics | discolored and more matte | discolored and more matte | fillers swell and surface mottles with solvents | phenol and formaldehyde with severe degradation |
| Polyolefin (polyethylene, polypropylene) | yellowed, brittle | resistant | swollen by some organics | none |
| Polystyrene | yellowed, brittled | resistant | dissolved, swelled, stress cracked | none |
| Polyurethane | yellowed, brittle, sticky, crumbles | yellowed, brittle, sticky, crumbles | swelled, stress cracked | nitrogenous organic gases and liquids |
| Polyvinyl chloride | yellowed, brittle | resistant | dissolved, swelled, embrittled by plasticizer extraction | oily plasticizer liquids, maybe hydrochloric acid gas under extreme conditions of moisture and light exposure |
| Rubber, ebonite, vulcanite | brittle, discolored, increase in matteness | hydrogen sulfide and other gases, sulfuric acid on surfaces | surface mottled by solvents | hydrogen sulfide and other sulfur-containing gases, sulfuric acid on surfaces |
| All plastics (and organics) | should be considered as prone to damage by ultraviolet radiation usually resulting in yellowing and embrittlement | condensation plastics like esters, amides, and urethanes are subject to hydrolysis with subsequent weakening | thermoplastics may dissolve, thermosets may swell, stress cracking | harmful gases from plastics with chlorine, sulfur, and pendant (not main chain) ester groups |
Additional effects of deterioration:
Plastics composed of cellulose acetate, when exposed to water, often will give off a smell of vinegar (vinegar syndrome); the surface will have a white powder residue and will begin to shrink. [15]
Cellulose acetate butyrate (CAB) and cellulose butyrate will produce butyric acid which has a "vomit odor". [3] [16]
Polyvinyl chloride may cause a "blooming" effect, white powder on the surface that can contaminate nearby materials. [3]
A yearly checkup of plastic artifacts can help monitor their condition, as well as the condition of the surrounding objects to verify that they have not been cross-contaminated. [17]
Impermeable safety gloves such as those made of nitrile can help prevent toxins from entering the skin when handling plastic objects. [1] Dust masks, respirators, or other personal protective equipment may be required for protection from outgassing or airborne microplastic dusts produced by some decaying plastics.
Plastics are best stored with a relative humidity level of 50%, at a storage temperature of 18 °C (64 °F), in light-proof enclosures. [17] Because the composition of each plastic material can be different, it is difficult to designate a single uniform storage care plan; understanding the specific composition of a plastic artifact can help determine its preferred climate conditions. [17] Keeping plastics at a stable low temperature and placing these objects either in cold storage or in oxygen-impermeable bags helps to slow degradation.
Monitoring plastics in their storage environment is done by tracking their status and condition by using log entries on spreadsheets or in another database. Monitoring the temperature environment is done using data logger hardware which tracks hourly changes in temperature (and optionally, humidity). Objects composed of flammable and unstable cellulose nitrate especially benefit from cold storage, to reduce their rate of decay. [3]
Adsorbents such as activated carbon, silica gel, and zeolites are used to absorb gases that are released from plastics. [17] These absorbents can also be used when the object is on display to prevent and off-gassing that could occur, whether the object is on exhibit or in long-term storage. Absorbents along with acid-free boxes can help slow down the process of degradation and vinegar syndrome which is common in certain types of film, Lego plastics, and artwork.
Oxygen-impermeable bags are used to exclude atmospheric oxygen. In combination with oxygen absorbers, this prevents oxidation and deterioration of the contents. [17]
The process of conservation and restoration of plastics requires an understanding of chemical composition of the material and an appreciation for the possible methods of restoration and their limitations, as well as development of a post-treatment preventive care plan for the object.
The process of cleaning plastics is done with the use of appropriate solvents, after identifying the polymers that make up the composition of the plastic. [18] A spot test can be performed if there is uncertainty how the object will react to water or solvents.
Within the field of contemporary art, where the surface finish is part of the artist's intent, the removal of scratches may need to be more nuanced, compared to simply compensating for accidental damage to social-historical artifacts. Conservators have developed and scientifically investigated a variety of methods for scratch removal. [19]
Fillings may be needed if an object has suffered considerable loss of material due to accidental damage or chemical deterioration. The process of filling depends on the object's chemical composition, and requires consideration of refractive indexes, transparency, viscosity, and its compatibility with the rest of the object. [20]
The conservation and restoration of cultural property focuses on protection and care of cultural property, including artworks, architecture, archaeology, and museum collections. Conservation activities include preventive conservation, examination, documentation, research, treatment, and education. This field is closely allied with conservation science, curators and registrars.
Vinegar syndrome, also known as acetic acid syndrome, is a condition created by the deacetylation of cellulose acetates and cellulose triacetate. This deacetylation produces acetic acid, giving off a vinegar odor that gives the condition its name; as well, objects undergoing vinegar syndrome often shrink, become brittle, and form crystals on their surface due to the migration of plasticizers. Vinegar syndrome widely affects cellulose acetate film as used in photography. It has also been observed to affect older magnetic tape, where cellulose acetate is used as a base, as well as polarizers used in liquid-crystal display units and everyday plastics such as containers and tableware. High temperatures and fluctuations in relative humidity have been observed to accelerate the process. The process is autocatalytic, and the damage done by vinegar syndrome is irreversible.
With respect to cultural property, conservation science is the interdisciplinary study of the conservation of art, architecture, technical art history and other cultural works through the use of scientific inquiry. General areas of research include the technology and structure of artistic and historic works. In other words, the materials and techniques from which cultural, artistic and historic objects are made.
A conservator-restorer is a professional responsible for the preservation of artistic and cultural artifacts, also known as cultural heritage. Conservators possess the expertise to preserve cultural heritage in a way that retains the integrity of the object, building or site, including its historical significance, context and aesthetic or visual aspects. This kind of preservation is done by analyzing and assessing the condition of cultural property, understanding processes and evidence of deterioration, planning collections care or site management strategies that prevent damage, carrying out conservation treatments, and conducting research. A conservator's job is to ensure that the objects in a museum's collection are kept in the best possible condition, as well as to serve the museum's mission to bring art before the public.
The conservation and restoration of ivory objects is the process of maintaining and preserving objects that are ivory or include ivory material. Conservation and restoration are aimed at preserving the ivory material and physical form along with the objects condition and treatment documentation. Activities dedicated to the preservation of ivory objects include preventing agents of deterioration that specifically connect with ivory as a material, preventative conservation, and treatment of ivory objects. Conservators, curators, collections managers, and other museum personnel are in charge of taking the necessary measurements to ensure that ivory objects are well maintained and will make the decision for any conservation and restoration of the objects.
Conservation and restoration of movable cultural property is a term used to denote the conservation of movable cultural property items in libraries, archives, museums and private collections. Conservation encompasses all the actions taken toward the long-term preservation of cultural heritage. Activities include examination, documentation, treatment, and preventive care, which is supported by research and education. Object conservation is specifically the actions taken to preserve and restore cultural objects. The objects span a wide range of materials from a variety of cultures, time periods, and functions. Object conservation can be applied to both art objects and artifacts. Conservation practice aims to prevent damage from occurring, a process known as 'preventive conservation'. The purpose of preventive conservation is to maintain, and where possible enhance, the condition of an object, as well as managing deterioration risks, such as handling and environmental conditions. Historically, object conservation was focused on the category of fine arts but now many different types of objects are conserved. Each type of object material, typically denoted by organic or inorganic then the specific medium, requires a specialized professional conservator and often requires collaborative work between museum staff, scientists, and conservators.
Conservation and restoration of ceramic objects is a process dedicated to the preservation and protection of objects of historical and personal value made from ceramic. Typically, this activity of conservation-restoration is undertaken by a conservator-restorer, especially when dealing with an object of cultural heritage. Ceramics are created from a production of coatings of inorganic, nonmetallic materials using heating and cooling to create a glaze. These coatings are often permanent and sustainable for utilitarian and decorative purposes. The cleaning, handling, storage, and in general treatment of ceramics is consistent with that of glass because they are made of similar oxygen-rich components, such as silicates. In conservation ceramics are broken down into three groups: unfired clay, earthenware or terracotta, and stoneware and porcelain.
Collection maintenance is an area of collections management that consists of the day-to-day hands on care of collections and cultural heritage. The primary goal of collections maintenance or preventive conservation is to prevent further decay of cultural heritage by ensuring proper storage and upkeep including performing regular housekeeping of the spaces and objects and monitoring and controlling storage and gallery environments. Collections maintenance is part of the risk management field of collections management. The professionals most involved with collections maintenance include collection managers, registrars, and archivists, depending on the size and scope of the institution. Collections maintenance takes place in two primary areas of the museum: storage areas and display areas.
The conservation and restoration of books, manuscripts, documents, and ephemera is an activity dedicated to extending the life of items of historical and personal value made primarily from paper, parchment, and leather. When applied to cultural heritage, conservation activities are generally undertaken by a conservator. The primary goal of conservation is to extend the lifespan of the object as well as maintaining its integrity by keeping all additions reversible. Conservation of books and paper involves techniques of bookbinding, restoration, paper chemistry, and other material technologies including preservation and archival techniques.
An Objects conservator is a professional, working in a museum setting or private practice, that specializes in the conservation of three-dimensional works. They undergo specialized education, training, and experience that allows them to formulate and implement preventive strategies and invasive treatment protocols to preserve cultural property for the future. Objects conservators typically specialize in one type of material or class of cultural property, including metals, archaeological artifacts, ethnographic artifacts, glass, and ceramic art. Objects conservation presents many challenges due to their three-dimensional form and composite nature.
The conservation and restoration of clocks refers to the care given to the physical and functional aspects of time measuring devices featuring "moving hands on a dial face" exclusive of watches. Care for clocks constitutes regulating the external environment, cleaning, winding, lubrication, pest-management, and repairing or replacing mechanical and aesthetic components to preserve or achieve the desired state as specified by the owner. Clocks are typically composed of multiple types of materials such as wood, metal, paint, plastic, etc., which have unique behaviors and environmental interactions, making treatment options complex. The materials used and the complexity of clockwork warrant having a Horological Conservator complete the work.
The conservation and restoration of painting frames is the process through which picture frames are preserved. Frame conservation and restoration includes general cleaning of the frame, as well as in depth processes such as replacing damaged ornamentation, gilding, and toning.
The conservation and restoration of flags and banners is the process by which conservators work to preserve and restore flags and banners from future deterioration and damage. As a part of Conservation of Textiles, flag and banner conservation require the care of a skilled and well trained textile conservator, specifically trained in historical materials.
Textile stabilization is a conservation method for fiber and yarn-based cloth intended to mitigate damage, prevent degradation and preserve structural integrity. Stabilization is part of a broad set of techniques in the field of conservation and restoration of textiles typically undertaken by a specialist or textile conservator. Appropriate treatment is determined through risk assessment and close examination of a textile's characteristics and the nature of the damage. Organic and synthetic fibers become weak due to age, handling, and environmental exposure and display physical deterioration such as fraying, planar distortion, loss, and change in surface character. Treatment involves reinforcing tensile strength and reintegration of parts for aesthetic, functional, and historic preservation. Methods can include stitching, darning, reweaving, and the attachment of supports through overlays and underlays. Hand-sewing follows the mantra of “gently does it” using fine needles, supple yarns, and a light touch. Heavily damaged and fragile fabrics often require stabilization through adhesive consolidation, though this is less common. It is essential that conservators consider physical and chemical compatibility along with future treatability in choosing a stabilization technique.
Conservation-restoration of bone, horn, and antler objects involves the processes by which the deterioration of objects either containing or made from bone, horn, and antler is contained and prevented. Their use has been documented throughout history in many societal groups as these materials are durable, plentiful, versatile, and naturally occurring/replenishing.
The conservation and restoration of paintings is carried out by professional painting conservators. Paintings cover a wide range of various mediums, materials, and their supports. Painting types include fine art to decorative and functional objects spanning from acrylics, frescoes, and oil paint on various surfaces, egg tempera on panels and canvas, lacquer painting, water color and more. Knowing the materials of any given painting and its support allows for the proper restoration and conservation practices. All components of a painting will react to its environment differently, and impact the artwork as a whole. These material components along with collections care will determine the longevity of a painting. The first steps to conservation and restoration is preventive conservation followed by active restoration with the artist's intent in mind.
The conservation and restoration of film is the physical care and treatment of film-based materials. These include photographic film and motion picture film stock.
The conservation-restoration of panel paintings involves preventive and treatment measures taken by paintings conservators to slow deterioration, preserve, and repair damage. Panel paintings consist of a wood support, a ground, and an image layer. They are typically constructed of two or more panels joined together by crossbeam braces which can separate due to age and material instability caused by fluctuations in relative humidity and temperature. These factors compromise structural integrity and can lead to warping and paint flaking. Because wood is particularly susceptible to pest damage, an IPM plan and regulation of the conditions in storage and display are essential. Past treatments that have fallen out of favor because they can cause permanent damage include transfer of the painting onto a new support, planing, and heavy cradling. Today's conservators often have to remediate damage from previous restoration efforts. Modern conservation-restoration techniques favor minimal intervention that accommodates wood's natural tendency to react to environmental changes. Treatments may include applying flexible battens to minimize deformation or simply leaving distortions alone, instead focusing on preventive care to preserve the artwork in its original state.
The Modern and Contemporary Art Research Initiative is a program started by the Getty Conservation Institute (GCI). It began in 2007 in response to the variety of new materials and technologies being used by contemporary artists in their work, and the lack of known conservation treatments for these new materials. This area was seen as a gap in the field of conservation, but also posed unique challenges when considering the intention of the artist and the physical aging that his or her materials might endure. According to Thomas F. Reese, "Conservators...must enter into the critical spirit of the works themselves if they are to save and transmit not merely decontextualized fragments but their essence to the future."
The conservation and restoration of wooden artifacts refers to the preservation of art and artifacts made of wood. Conservation and restoration in regards to cultural heritage is completed by a conservator-restorer.