Emily Frank, Michaela Paulson, Pablo Londero, and Carol Snow
Abstract
This article documents a preliminary study on the use of an externally modified laser (Nd:YAG) to remove active chloride corrosion on copper alloys. Previous use of lasers in metals conservation has included removing coatings, unwanted patinas, and surface accretions, but little published literature exists on the systematic testing of laser spot treatment of bronze disease. This article describes our methodology and reports initial findings. We explore how laser cleaning might enhance existing treatment methods, allowing for increased efficiency and improved long-term preservation of copper alloy artifacts.
To be a flexible tool for the treatment of bronze disease, laser spot size must be independent of energy output, allowing the conservator to target only the afflicted area at the optimal fluence. Thus, our approach requires fine tuning fluence in relation to corrosion properties and surface preparation. For this study, we manipulated the fixed energy output of a Compact Phoenix Laser, without altering the handheld unit, through a series of lenses and a polarizer. The modified 1064 nm laser successfully micro-excavated pits of bronze disease. Examination of the treated samples with stereomicroscopy, scanning electron microscopy, and Raman spectroscopy indicates that this is a promising method. Micromelting of the copper alloy at the micron and sub-micron level on some samples requires further study.