Metal Exploration & Restoration

Challenges And Available Options

Architectural metals – a building’s jewelry, consisting of ornate grilles, panels, doors, cornices and sculpture – create visual delight through intrinsic and applied finishes. With the exception of iron, which is usually painted, decorative effects on metals are achieved with chemical patination, plating, coating and mechanical texturing to produce a wide variety of colors, patterns and finishes. Over time, however, the artistic intent can become lost through years of exposure to the elements, general wear and uninformed treatment. Restoring these often fleeting original finishes can be challenging, as they may leave little evidence behind. These challenges can be met through examination and analysis of the existing finishes on site, in the laboratory, and through archival research.

The intrinsic color and tactile qualities of architectural metals such as bronze, copper, aluminum, gold, lead, nickel, silver, tin, zinc and titanium are frequently enhanced through chemical manipulation and coatings. These finishes are superficial, ephemeral and, when left unprotected or unmaintained, subject to rapid deterioration from exposure or wear. Because patinas and plating on metal are considerably thinner than paint or varnish, they do not accumulate in a series of successive strata. Unlike paints, patinas will oxidize when exposed to the environment. The result is both a physical and chemical change in the patina that leaves no readily observable evidence of the original appearance.

Finishes on building exteriors are often lost to environmental exposure, while interior surfaces are frequently altered by repeated wear or aggressive maintenance. An historic finish may be replaced by a new one that reflects a current trend or a new owner’s preference or a generic metal finish that is easier and more cost effective to maintain. Either way, the elimination of evidence of the historic scheme is the same.

Our conservators partially disassembled one of the panel groups at the David H. Koch Theater, revealing evidence of non-original, field-applied finishes and illustrating general construction techniques. A cleaning test at the theater illustrates the corrosion and soiling that have accumulated over the original oxidized metal finish.

Looking for Evidence
When an owner or building manager decides to preserve or restore decorative metals to their original appearance, the primary challenge is determining what the original finish actually was. At this point, a metals conservator can take on the difficult forensic task of identifying meaningful historic evidence and deciphering original artistic intent to faithfully restore these finishes. A systematic in-situ study of the metal elements, combined with a fundamental understanding of the methods and materials used to create the decorative finish, lays the foundation for a fruitful investigation.

Original finishes may be found intact in protected or concealed locations. On exteriors, original finishes may have become encapsulated within later construction or under paint. Finishes may also be found under hardware or inside complex assemblages, where they are shielded from oxidation, weathering and maintenance. Evidence may exist in peripheral and under-used areas, such as inside closets and pipe chases, above soffits and within stairwells. Light fixtures and other elements that are difficult to reach – and difficult to refinish – may also retain original finishes.

Careful cleaning, disassembly or removal of overlying elements can help reveal the original treatment underneath. Further sampling and targeted laboratory analysis can provide additional insight. Elemental analysis of a sample through scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) or X-ray fluorescence (XRF) can confirm the identity of the metal substrate and determine alloy composition. Raman spectroscopy can be used to interpret corrosion products and mineral pigments. Where present, samples of coatings may be examined via polarized light microscopy to discern the types of binders and pigments used. At the National Academy of Sciences, a conservator prepared a mock-up of several hot-applied patinas to demonstrate the likely range of original patina appearances.

Once evidence is identified and interpreted, developing a comprehensive restoration plan can still be extremely difficult. Forensic observations usually identify some, but not all, of the original finishes of a building-wide program. In the absence of conclusive evidence, an educated and experienced metals conservator will supplement physical with documentary evidence, including plans, specifications, historic photographs and written accounts. Archival evidence serves as a cross-reference for physical evidence, helping to establish probable timelines of intervention and to aid the reconstruction of likely schemes. This process can be aided by the use of digitally modified photographs and field mock-ups, to illustrate alternative finishes before selecting and specifying a final treatment. Treatment recommendations should consider the desired appearance of the finish versus anticipated levels of exposure and wear and also accommodate protective coatings.

The conservator can work with the client to develop reasonable goals and expectations for the lifespan of the finish, as well as realistic projections of the owner’s desire or ability to perform routine maintenance. This may include educating clients about the vulnerability and limitations of metal surfaces and the finishes that can be applied to them.

To a building owner, the loss or alteration of an original decorative finish may appear to pose great challenges. However, this challenge can be overcome by working with a competent, sympathetic conservator. The case studies discussed below demonstrate the advantages of engaging a metals conservator early on in a project to facilitate an accurate and responsible restoration plan. The beauty, variety and subtlety displayed by a responsibly preserved or restored decorative metal finish are satisfying rewards to this partnership.


David H. Koch Theater
The restoration of the David H. Koch Theater at Lincoln Center in New York City includes the vast system of decorative panels and railings that encircle the atrium.  The David H. Koch Theater was designed by Philip Johnson as one of the anchors of the Lincoln Center for the Performing Arts and was completed in 1964. Its signature feature is a multi-story series of railings and highly decorative panels circling its atrium.

We attempted to discern the range of metals and historic finishes present, despite their worn condition and complex construction methods. Through careful observation, conservators determined that the panels were fabricated from ferrous wire dipped in brass to create hundreds of individual “splatter” pattern units – no two alike. The railing and framework were fabricated from architectural bronze and treated with a directional-sanded and oxidized finish. Cleaning tests using a variety of detergents and solvents confirmed that a protective lacquer was present. Variations in metal color and coating boundaries revealed the likely order in which the panels were assembled and hinted at factory- versus field-applied finishes.

We developed a preservation treatment plan to refresh the existing finishes and remedy minor areas of loss, due to years of wear. These methods included: cleaning using a mild detergent with added corrosion inhibitors, chemical and mechanical corrosion removal and localized restoration of the dark oxidized finish. The goal was to subtly reintegrate these areas of finish repair into the overall decorative scheme, enabling Johnson’s original intent to continue to shine through.

The National Academy of Sciences
The National Academy of Sciences headquarters in Washington, DC, features an extraordinary use of decorative metals, including these monumental windows with decorative spandrel panels, enlivened with a rich verdigris patina. The National Academy of Sciences displays an ambitious program of interior and exterior decorative metals, ranging from handrails to monumental windows and sculptural spandrel panels. The metals exhibited a wide array of finishes in different colors, patterns and states of deterioration. The existing metals were studied via probes and by the careful removal of paint, layer by layer. On-site evidence was painstakingly cross-referenced with historic photographs and records. The investigation revealed that the original scheme was a subtle and complex program of artificially weathered patinas in various colors, intermixed with sculptural relief panels in contrasting tones. The result was an amalgamation of finishes that reflected the times and tastes of two significant phases: the original construction, attributed to Bertram Goodhue in 1924, and to Harrison and Abramovitz, who added wings in the 1960s and also implemented changes to the historic structure.

The treatment plan was designed – and mocked up – to recreate the decorative finish original to each building phase. All surfaces required general cleaning and surface preparation, including localized removal of corrosion. This was followed by patination, whereby the desired color and pattern of each are carefully developed through successive applications of a dilute chemical solution. Different formulas and application techniques were developed to achieve colors ranging from rich browns and emerald greens to light verdigris. Both lacquer and wax coatings were recommended to prolong the life of the finish.