Radios: from Bakelite to silicone rubber

Christina Elsässer, Marisa Pamplona and Tim Bechthold

The design and materials applied in the production of radios have changed drastically since the 1930s, from wooden casings resembling furniture made by handcraft to plastic casings varying in style and mass-produced by the industry. Even though plastics have shaped radio casings and other technical components for several decades, museums know little about the used polymers. This information is fundamental in helping conservators and museum managers plan conservation strategies for the preservation of radio collections.
This research study characterizes the plastic materials applied in seven radios by using a comprehensive methodology: i) production features detectable by visual examination ii) material identification by analytical techniques iii) deterioration phenomena present. Preventive conservation measures were suggested accordingly.
The selected models were produced between 1934 (beginning of mass production of plastic radios) and 1996 (emerging of internet radio and smartphones, which take over the tasks of former radios). The models were opened and their plastic components (casings, operating elements, cables, handle) were observed and sampled. The synthetic polymers were identified by means of Infrared and Raman spectroscopy and optical microscopy. Deterioration patterns were described based on condition survey forms suggested in the literature.
Results show that the signs of production processes help to indicate the type of plastic used (thermoset, thermoplastic and elastomer). Furthermore, the number of plastic components and the ways these were assembled help to understand the amount of steps required to mount a radio. Material analysis of casings point out that thermosets (e.g. phenolformaldehyde) were replaced by thermoplastics (e.g. styrene and polymethylmethacrylate), whereas thermoplastics (polyvinylchloride) kept being used in handles. The deterioration forms present on the radios fit well with those described in the literature for plastics.
Preliminary results of this investigation will soon be compared and discussed with new data gathered on production features, time of production, archival research and specific deterioration forms from a collection of radios made of plastic. We aim to contribute to a classification scheme that allows estimating the synthetic polymers most likely to be present in radios without the use of analytical tools.