This talk, given by Dawn Wallace, caught my eye because it focused on a treatment that I had heard of, but largely amongst doll collectors, not amongst conservators – and I had never had the guts to try it! The use of acne treatments, such as gels containing salicylic acid and benzoil peroxide, to reduce or remove copper staining has really interesting potential, but was not previously well-tested. Dawn treated various PVC dolls (including Barbie!) and completed analysis using pyrolysis GC/MS, XRF, and mass loss/mass attenuation. The results showed that for most gels, there was movement of copper within the stain, although with some there were changes to the plastic makeup. The salicylic acid did remove copper, but showed a slight weight gain rather than a weight loss – pyrolysis GC/MS then confirmed that a residue had indeed been left on the surface. The benzoil peroxide showed significant weight loss, but had its downsides as well.
Although this was a quick talk (15 minutes), I found it very informative and enjoyable. I would have liked to see more visual comparisona of the before and after treatment, as I wonder if the success in removing the stains is enough to make it worth pursuing removal of the residue as an additional treatment. I will be interested in any future research into this treatment!
Course Leaders: Thea van Oosten, former senior conservation scientist at the Cultural Heritage Agency of the Netherlands (RCE) since 1989, currently retired and freelancing and Anna Laganà, lecturer at the University of Amsterdam and freelance conservator / researcher specialized in the conservation of plastics. Both were entertaining educators throughout the course.
This is a short review of the above plastics workshop which took place as a collaborative professional development program between the University of Amsterdam and the Cultural Heritage Agency of the Netherlands (RCE). The four day course combined theory and practice, as well as input from the ten participants from seven countries regarding the challenges they are encountering with plastics materials.
An overview of the development of plastics from the 19th century to present day was reported including the chemical properties and manufacturing processes which create the various types of plastics materials. This was useful in determining what type of plastics you may be working with and how this influences degradation and therefore future preservation protocols. Understanding the difference between three main characteristics of thermoplastics, thermosets and elastomers and their polymeric makeup made sense when thinking about characteristics and deterioration patterns. The impact of additives, such as fillers, pigments and plasticizers used to manipulate the properties of plastics materials can have drastic effects on the aesthetic aspect, touch and life span of many plastic objects. These are considered the internal factors that gear the longevity of synthetic materials. External factors like oxygen, ozone, light and temperature cause oxidative degradation and hydrolysis of plastic objects initiating catalytic reactions and can accelerate deterioration. Scary stuff! But in the safe hands of Thea and Anna we motored on.
The five most vulnerable plastics: cellulose nitrate, cellulose acetate, poly (vinyl chloride), natural rubber and polyurethane were highlighted. These plastics are known to show significant deterioration patterns in short periods of time. Chemical breakdown, physical and mechanical damage and also, biological damage are often documented with these kinds of plastics. Theory sessions encompassed plenty of handling sessions using examples from reference collections donated to the RCE by Thea van Oosten. This exercise helped to familiarize participants with various plastics materials produced through history by feeling, smelling and listening to the sound plastics make when dropped. Density and color were other considerations. Film clips of manufacturing processes and artists using and manipulating plastic products to produce works of art were shown.
Ron Mueck – videos: https://www.youtube.com/channel/UC4tUoKVLJ8j6onJ2C5ytdGQ
Practical sessions included the impact of solvents on various plastics types. Deionized water and white spirit (organic clear solvent made with a mixture of hydrocarbons) seemed to have the least effect, whereas acetone showed significant physical change. Great fun was had examining residual strains in clear and translucent plastics using a strain viewer. This instrument provided a fabulous myriad of colors which enabled the examiner to measure the internal stress areas. Learning adhesive and consolidation methodologies provided good pragmatic solutions to repair and stabilize plastic objects that are physically or mechanically damaged. Understanding surface energy of plastic surfaces (low energy a water droplet will remain on the surface, high energy the water droplet will disperse evenly) was useful to know when thinking about adhesion levels and prevention of causing further internal stress and strain. There was dedicated sessions to the specific properties and consolidation of polyurethane foam as this material can degrade quickly depending on its polymeric make-up. Cleaning strategies were reviewed and practical sessions included the effects of dry cleaning methods, solvents and mild detergent solutions on various plastics materials.
Preventive guidelines were discussed; display parameters of 50- 150 lux (5-14 foot-candles), dark conditions preferred in storage, 50%RH, a temperature of 18-20 centigrade (64.4-68 Fahrenheit), good ventilation to prevent a build-up of gaseous degradation products from off-gassing plastics and maintaining a low temperature to help slow down the degradation process. Oxygen scavengers were mentioned as a useful product to help maintain a good environment. Encapsulating rubber objects was also demonstrated in order to slow down the deterioration of rubber being one of the most vulnerable plastics.
All participants were provided with a folder with useful theory, a bibliography and documentation of the presentations that were given during the course. One of the most useful sections for me were the tables reflecting the solubility parameters and chemical resistance of plastics, these would certainly help when deciphering appropriate cleaning systems if appropriate at all. I would certainly consider the use of micro emulsions and gels as other applications which were not included in the workshop. Also, the data sheets referring to adhesive properties and their appropriateness to various plastic types would be a good reference point to selecting adhesive and consolidation treatments. All provided good starting points for investigation.
With many thanks to Thea and Anna, they were both marvelous!
Attending a lecture by Yvonne Shashoua, Senior Researcher in the Department of Conservation at the National Museum of Denmark, was such a treat, since she is so well-known in the field of plastics conservation, and her session did not disappoint. Her calm, precise, and very approachable speaking style was impressive as she covered a scientific discussion on her current research into cellulose acetate degradation and its interaction with gas absorbents. Since she will be presenting her findings in upcoming journals, I will only briefly go over what I learned and what you missed at this Research & Technical Studies AIC session.
Shashoua began by reminding us that plastics comprise an increasing proportion of museum collections. Since it is difficult to detect plastic degradation until it reaches an advanced stage, a preventative approach, by either removing the factors causing or accelerating degradation, is usually taken. Gas absorbents (silica gel, activated charcoal, Zeolite 4A, and Corrosion Intercept) are frequently used in museum storage and display situations to create a microclimate by removing specific gases. She discussed how these materials are used and how they absorb pollutants, which I found very interesting.
Focusing on cellulose acetate, Shashoua discussed the mechanism of degradation (and the breakdown by-product acetic acid) and how additives (plasticizers and fire retardants, which are weakly bonded within the matrix) migrate out ultimately ending in shrinkage. She was curious why the degradation process even begins in a museum environment, which began her in-depth research project. Cellulose acetate, has been used since 1910, but by the 1960s could be found in many objects: imitation mother of pearl, cigarette filters, early Lego bricks, movie film bases and rayon. By conducting a systematic study on the adsorbents’ interaction with cellulose acetate, she has found some startling results. The adsorbents in some cases did slow down the onset of autocatalysis, however some also adsorbed the plasticizer and/or flame inhibitor, resulting in damage. Her results suggest that commonly used absorbents in museums are non-specific and ineffective for cellulose acetate and, by extrapolation, other plastics. She did rate the adsorbents on a sliding scale; so reading her more in-depth post-prints will be a good lesson and/or review for all of us. All this is startling news! An archival acid-free box might simply be the best defense. Wow. I cannot wait to read her in-depth post-prints and journal articles concerning this fascinating subject.