Identification of Plastic Materials: A conversation with Brenda Keneghan

We spoke to Brenda Keneghan, a conservation consultant in modern materials and West Dean’s Identification of Plastic Materials course tutor about the historical development of plastics, the future of plastic artefacts in museums, and the challenges and considerations facing plastic preservation.

Can you provide insights into the historical development of plastics and how their profile has evolved over time?

Although most people think that plastics are a relatively new phenomenon, they were in fact invented almost two centuries ago in the mid-19th century. A common misconception is that plastic is a single material. In fact, there are very many different types of plastics with differing properties. The first materials created were semi-synthetic imitators of natural materials. These semi-synthetics such as Cellulose Nitrate were made by chemically modifying natural materials like cellulose. Cellulose Nitrate was used to imitate natural materials such as ivory, amber, tortoiseshell, etc, which were becoming rarer and thus more expensive. The first completely synthetic plastic was Bakelite, invented in the early part of the 20th century. Most people are familiar with this dark material which was used in many electrical appliances like radios and clocks because it had very good insulating properties. The disadvantage of Bakelite, however, was that it could only be produced in dark colours. This disadvantage was soon overcome and although plastics have since developed into materials in their own right, they are still often dogged by a reputation as imitators and/or shoddy materials. In general, they are not given the same respect as naturally occurring materials. More recently plastics have been demonised for their contribution to environmental problems. But people forget the great contribution that plastics have made in many fields including healthcare, communications and electronics, to name but a few.

How do plastics commonly occur in heritage collections, and what are some significant considerations for conservators and curators regarding their preservation?

Plastics are found in almost all heritage collections ranging from ethnographic to modern art. They are very commonly found in art and design collections, fashion, toys, transport, archives. In fact, it is rare to find any collection without some plastic component. Despite being viewed as “lasting forever” and being the cause of environmental concerns, certain plastics do degrade. As stated above early plastics were often produced to imitate natural materials. Thus, curators are not always aware that they may have plastics in their collections. Unfortunately, it is these early semi-synthetic materials which often degrade. Their degradation is often accompanied by the production of acidic vapours which may cause damage to other objects in their vicinity. It is essential, therefore, to make people aware of the many guises of plastic materials, their potential instabilities and the dangers these may pose for other objects in collections.

In your experience, why is it important to identify plastic materials, and how can understanding their vulnerabilities help in protecting heritage collections?

As already stated there are very many different kinds of plastics and they have different stabilities - the early semi-synthetics being most vulnerable to degradation. Curators may not be aware of the existence of plastics in their collections. Many surveys have been undertaken over the past 25 years which have demonstrated that there are 5 plastic materials commonly found in collections which degrade regardless of what form the object takes. Some of this degradation can be detrimental to other objects or even to the fabric of the cases they are stored or displayed in. Therefore, it is important to know what materials are in your collections. If you have objects made from unstable plastics, controlling the environment can slow down degradation and extend the lifetime of the objects. If they have visibly degraded then they should be isolated from the general collection.

Could you share examples from collections you have worked on that illustrate the importance of plastics in collections and the challenges around its conservation?

I once worked with a collection of objects from theatre and performance. The collection included costumes and props. The curator was unconcerned and had previously informed me that there were no plastics or problems with plastic in their collection. I was highly sceptical especially as theatrical props were often made with cheap materials and not designed to last much after the performances. The curator called me and asked me for advice concerning an object she had found in storage. It was a decorative necklace with very large “amber” beads. Some of these beads had become dense and “sugary” in appearance. Some had broken into pieces. Metal components had become corroded. The acid-free tissue wrapping the object was shredded into small pieces. The cord holding the object together was broken and all the elements were loose in the box. The object had been made in 1927 and the beads were made from Cellulose Nitrate which had degraded and off-gassed acidic vapours. These acidic vapours had caused the damage to the components and the packaging. It was too late to save this object but it was an extremely good example of curators being unaware of the materials in their collection and the damage that plastic may cause.

Considering the prevalence of plastics in contemporary society, how do you envision museums navigating the acquisition and curation of plastic artifacts in the future?

I think the most important issue when acquiring a plastic object is the know the exact composition – i.e. what plastic it is made from. This allows informed decisions to be made. Different plastics may require storage and display at different environmental conditions. If the nature of the material is known, then a prediction of the potential lifetime and/ or future conservation costs necessary can be made. Some plastics have a predicted lifetime of ~ 50 years. This is significantly less than lifetimes of more traditional materials. As budgets shrink, museums may decide not to acquire all objects with such short lifetimes that may incur future costs.  Methods of recording some of these objects may be the preferred option over acquisition.

As plastic artifacts continue to age and degrade, what are the most pressing challenges museums will face in conserving and preserving these materials for future generations, and how do you envision the field of conservation adapting to address these challenges?

In addition to the materials degrading naturally, we are now faced with biodegradable plastics – that is those designed to degrade. Although not produced for artworks, it is inevitable that artists will use these materials to produce works. So, conservators will be faced with this additional problem. There is also the current issue of production by 3D printing methods. We do not know if this method introduces any weakness into the objects. It is an area that needs research. An area of current research is the use of nano-membranes to protect objects and works of art. These membranes have the potential to protect plastics against uv light degradation.

I think that in general the preservation of plastics may take a different approach to that of other materials. “Preventive conservation” by controlling the environment may be the only possible approach for these unstable materials. Also, the accepted premise of treatment reversibility may not be possible for some experimental approaches.

What should people expect from the Identification of Plastic Materials course? What will the course involve, what might they learn and how can this be applied in their professional practices?

The aim of the course is to enable anyone working in collections to identify the 5 unstable plastics that might be present amongst their objects, without using analytical instrumentation. Identification will be demonstrated by observing and handling objects. No previous knowledge of plastics is required. The course will consist of presentations, lab demonstrations and practical handling/identification sessions.

By the end of the course the participants should be able to assess their collections and identify any potentially harmful plastics. They will approach a collections care system based on the knowledge they have gained from the course. This will enable them to put preventive measures in place if necessary.