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Field Notes: Conservation Students Learn Laser Cleaning Techniques
Evan Oxland, a second-year student in the Graduate Program in Historic Preservation at PennDesign, filed this report.
On April 29, the Graduate Program in Historic Preservation hosted objects conservator Adam Jenkins to present on laser cleaning of architectural materials and provide a demonstration of the equipment. The group included those students currently following the conservation science track as well as recent graduates. The program began with the history, use, and technology of lasers as well as a brief introduction of laser ablation methods.
Laser technology has been used in the treatment of art and architecture for the last 3 decades; however, new advances in the equipment and its availability have made its use as a conservation tool practical. Interestingly, heritage and art conservation only represent a minute fraction of the laser market; the industry being dominated primarily by medical and industrial applications.
Jenkins offered a survey of laser ablation systems which utilize different matter to produce an aplificed beam of light. These systems create energy that span from UV to IR light spectrums (visible and invisible light) and include, Gas Lasers, Dye Lasers, Solid State: Ruby, Nd:YAG, & Er:YAG lasers, M.A.P.L.E., and LQS lasers.
The proprietary laser systems used for art and architectural conservation are primarily solid state lasers which are generally categorized by the way in which they distribute the light energy (stationary optic and scanning optic lasers).
Jenkins did note that lasers, like any tool, can be abused. Often the successful cleaning of an object or architectural feature will involve a combination of treatment methods in concert with laser. Conservation methodology always begins with first understanding soiling and the material properties of the substrate below. From there, methods and materials are selected for testing that will clean effectively while minimizing damage to the substrate. If laser is selected as a tool, testing is always necessary to determine the type of laser, energy profile, and operational parameters. Jenkins also included practical advice regarding health and safety concerns, costs, as well as the technical and logistical opportunities and limitations of the different systems.
The group also had the opportunity to work with the portable CL-20 Scanning Optic Laser manufactured by Adapt Laser Systems. This equipment has been useful for object conservation because of its low power level but has limited applications on an architectural scale. The group had a chance to use the laser to remove a variety of soiling types from an array of historic architectural materials including ferrous and cuprous metals, marble, sandstone, granite, brick, and terracotta.
Because laser energy behaves similarly to visible light, it will be absorbed by dark materials and will reflect off light materials. For instance, if words were written with pencil on a white piece of paper the laser could remove the graphite without damaging the paper. The students, many of whom took time away from their theses to attend this program, were able to write the word “THESIS” and then use the laser to ablate the text. A cathartic release!
Bisotun, in western Iran’s Kermanshah province, is notable for its inscription carved on a limestone cliff. "It is unique, being the only known monumental text of the Achaemenids to document a specific historic event, that of the re-establishment of the empire by Darius I the Great," according to UNESCO. Image Bisotun AG-ChapelHill, Getty Images/iStockphoto