Damage function for silk fabric

Damage functions are a modelling tool to assess the impact of external and internal stressors on heritage. Despite its importance, silk remains little researched in this respect. The impact of tin-phosphate weighting, used to increase the weight of silk applied in the 19th and early 20th centuries, on the chemistry and kinetics of degradation is still unknown. To fill this gap, we conducted degradation experiments demonstrating that while weighting increases silk pH and makes it more chemically stable, it does not change the mechanism of degradation, which is dominated by hydrolysis. Isoperms and isochrones, the latter equipped with uncertainty intervals calculated using Monte-Carlo simulations, are provided based on the determination of the damage threshold, determined using manual tests conducted by conservation experts. Validation and applicability of the developed models are discussed. The models show that acidic silk is at particular risk and requires colder and drier storage environments.