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Insider’s Look at Conservation at the National Gallery of Art

Unveiled is excited to host our first guest post from the National Gallery of Art. The author, Katy May, is an object conservator with extensive experience in the care and treatment of outdoor sculpture and has been at the National Gallery of Art since 1997. 

Knife Edge Mirror Two Piece by Henry Moore was commissioned for the opening of the East Building of the National Gallery of Art in 1977, and has stood outside the entrance to the East Building since 1978. While it has never moved from this location, the sculpture has had a long and complex condition history.

The bronze sculpture was fabricated on a tight deadline by the English foundry Morris Singer, rather than the German founder who cast most of Moore’s monumental works, and is constructed from sand-cast panels welded together, with an applied chemical patina (a thin mineral surface layer produced by applying specific chemicals to the bare metal).  Flaws in the casting, fabrication, and finishing of the sculpture were noted almost immediately, and National Gallery conservators have long struggled to maintain the sculpture as Moore intended.

Flaws in the casting, fabrication, and finishing of the sculpture were noted almost immediately

National Gallery conservators have a full maintenance program for all outdoor works in the collection, but even with regular maintenance the surfaces on outdoor sculptures deteriorate over time and more intensive treatments are sometimes required to preserve the artist’s intent.  In the case of Knife Edge Mirror Two Piece, the existing patina had darkened dramatically, was streaked and uneven, and the welds had become progressively more visible.  In consultation with National Gallery experts and officials, the decision was made to re-patinate the sculpture and return the surface to the transparent golden patina intended by Moore.

Planning and testing of treatment methods took almost two years.  Conservators worked with curators to determine the intended appearance for the sculpture based on archival records, photographs of the sculpture in 1978, and based on the maquette – a highly finished preparatory work for the monumental sculpture.  A specialized outdoor bronze conservator was contracted to work with National Gallery conservators, and numerous tests were performed investigating a variety of patinating chemicals and application methods.

The sculpture is huge, measuring almost 18 feet tall and over 23 feet wide, with seemingly endless surfaces.

In early August 2014, conservators began the daunting project to re-patinate Knife Edge Mirror Two Piece, working on-site at the entrance to the East Building.  The sculpture is huge, measuring almost 18 feet tall and over 23 feet wide, with seemingly endless surfaces.  Each treatment step was performed by hand, working inch by inch, across, over, and around the two elements. Conservators removed old coatings, completely removed the deteriorated patina, and applied a series of patinating chemicals chosen to produce a new patina with the appropriate color range and level of translucence.  Throughout the treatment, conservators struggled with issues related to the low quality of casting and finishing; extensive areas of porosity, variation in alloy composition, and impurities in the metal produced unexpected and undesirable results in some areas, leading conservators to re-work problem areas numerous times.

For the duration of the treatment, the sculpture was fully enclosed in scaffolding with a water-resistant scrim overlay, to contain the treatment area and to ensure that the surface of the sculpture remained dry throughout the patination process.  Before the enclosure could be removed, a protective wax coating was applied by brush over all treated surfaces.

On October 10, 2014, after more than 8 weeks, the enclosure was removed, revealing the completely transformed sculpture.







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