Assessment of the deterioration process of copper alloys: a case study of Central Lithuanian crossbow brooches with a triangular foot

The deterioration and degree of preservation of copper alloy archaeological artefacts depends on several interacting factors that began when the artefacts were buried and continue in museum storage. Ageing and deterioration processes that have begun can be slowed, but not completely stopped. The influence of the type of copper alloy and museum environment storage conditions on deterioration processes was investigated. Crossbow brooches with a triangular foot were examined using non-destructive techniques such as portable XRF and radiography, as well as the data from excavation reports. The collected data on museum storage environment was analysed using the software program Eclimatenotebook. Based on the results of this analysis, the future preservation level was calculated using the risk assessment method. Most of the brooches examined were made of brass and were in a fairly good condition. The foot and pin were the most damaged parts. Future storage conditions with a high relative humidity (up to 80%) pose a great risk to the treated and untreated brooches.