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The assassination of US President John F. Kennedy on November 22, 1963 transformed the US political landscape as
well as the trajectory of subsequent world history. The venue of that tragic event in Dallas was Dealey Plaza,
encompassing the "grassy knoll" and the adjacent book-depository and courthouse buildings. For the past forty years the
site has undergone a series of conservation/preservation projects in order to make it more suitable for those visiting
either in homage or out of curiosity. One such project concerned the deterioration of ironwork within the "Old Red
Courthouse". The building architect noted that both stairway railings and floor-support trusses were corroding and
deteriorating at accelerating rates. In most situations of this sort the iron would be sandblasted and repainted. However,
in this instance sandblasting was inappropriate due to environmental concerns and logistical limitations. Furthermore,
historical authenticity criteria dictated that the metal be preserved with its original unpainted finish. In order to avoid
excessive floor loading (in this fragile old building) and the generation significant environmental air pollution (within
urban Dallas) the general contractor (Avery Mays, Inc.) opted to evaluate photonic divestment. Both laser cleaning and
laser glazing were assessed for efficacy and cost effectiveness. Xenon-flashlamp irradiation was evaluated both with and
without citric acid augmentation. Citric acid matrix-assisted flashlamp treatment was selected for the preservation of the
courthouse ironwork. This decision was based on three advantages over laser treatments: higher speed and cost
effectiveness, preservation of the historic "Oliver Foundry" logo markings, and the chemical passivation and rust
resistance of the final surface patina.
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