A preliminary investigation into the influence of archaeological material on the yellowing of polyethylene storage bags

Concerns around the degradation of plastics have been part of conservation discourse for decades. The spotlight is usually on art and objects, and conservation and display materials, however it could be argued that a significant volume of the plastics in museums is associated with storage bags. This study asked whether the condition of plastic storage bags might be influenced by what is stored inside them. If specific materials can be identified as more likely to affect plastic degradation, museums may have a lead-indicator for efficiently monitoring storage risks. This case study developed a methodology for applying multivariate analysis to collected data to answer this question. A subset of polyethylene self-seal bags used to pack archaeological material from the ‘Casselden Place’ assemblage at Museums Victoria was evaluated. Objective data were combined with subjective assessment of bag degradation features gathered during a collection survey and interrogated using multivariate statistical analysis. Results indicate (1) different levels of yellowing are associated with particular plastic bag stocks and (2) ceramic, slate and tile finds are more likely than other materials to be contained within yellower bags. The research points to future enquiry and demonstrates this methodology shows promise for extension to other large cultural datasets.