ABSTRACT
In 1989, paintings conservators at the Smithsonian American Art Museum were confronted by the vandalism of Morris Louis’ Beta Upsilon, a masterwork painting from his unfurled series (1960¬61). Comprised of colored bands of paint flowing inward from the edges on an unprimed canvas, the work was defaced with penciled graffiti lines on the raw canvas that mimicked the unfurling strokes of colors. Testing revealed the solution was not readily at hand at the time. Despite pressure to treat the artwork immediately, conservators persisted in finding the right solution. Laser cleaning was considered as a possible solution, but the correct parameters needed to be identified. Extensive testing was conducted on mockup samples using various pulse durations and wavelengths: 1064 nm, 532 nm, 355 nm, and 266 nm. After many years of preparation and testing, it was concluded that the 532 nm wavelength was appropriate for this particular cleaning problem. An entirely new laser cleaning system, the GC-¬532, was designed and built specifically to clean the Beta Upsilon. In order to allow great flexibility in laser parameter optimization the new bespoke laser system was built to have the 2nd harmonic 532nm, tunable pulse duration, pulse frequency, and pulse energy, an ultra¬high speed hot¬spot free circular scanner with tunable RPM, and various focal lens options. The research and testing leading up to the creation of a new purpose built green 532 nm pulsed laser system, the process of optimizing laser cleaning parameters, and the cleaning results achieved will be presented. This new laser technology will have future applications in cleaning canvases and organic materials.
