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Testing Protective Coatings and their Removal for Outdoor Bronze Statuary

Simmons, Tucker McIntosh

This research studied new coatings for their use on bronze statuary and evaluated removal using low-powered lasers. This testing was intended to add new coating materials to a conservator’s repertoire, to improve the protection of outdoor bronze sculpture, and extend the time between maintenance cycles. This would, in turn, allow owners to better care for their statues and lower long-term maintenance costs.

The most commonly used approach for coating outdoor bronze involves the use of wax and/or lacquer; both are considered to be easily reversible. Wax can be successfully removed with heat and water, while lacquers can be easily removed with standard solvents. Both wax and lacquer coatings’ life cycles are relatively short, with wax-coated bronze usually needing annual or biennial maintenance and lacquer coatings lifespan in the field lasting roughly three to five years. This reversibility, long considered to be important in the conservation community, has been a challenge with respect to long-term coating durability for works exhibited outdoors. Three coatings were chosen for testing in this project. All three were urethane-based clearcoats that are either applied to lacquer or directly to the patinated bronze.

A patina was applied to cast bronze coupons prior to the coatings. These samples were then subjected to accelerated weathering testing in a QUV chamber. After QUV testing, three procedures--based on ASTM standards--were conducted to assess the durability of the artificially weathered coatings. After the ASTM tests were concluded, removal of the surviving coatings was carried out using a 100-watt, 1064nm Class four laser. From these tests, it was determined that the acrylic urethane coating, Ecothane, produced by G. J. Nikolas & Co., was able to be successfully removed by laser cleaning, and could lead to a possible replacement for the commonly used wax and lacquers, however further research is needed before a definitive conclusion can be reached.

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More About This Work

Academic Units
Historic Preservation
Thesis Advisors
Trienens, Amanda B.
Degree
M.S., Columbia University
Published Here
July 2, 2021