Copper Guide Part 2: Copper Finishes, Patinas, and Textures

The surfacing of copper and copper alloys is an art form in itself. From the beginning, the mill undertakes a process to produce the finish on copper alloys that demonstrates care for the intrinsic beauty of this metal.

It seems almost a shame to develop a patina over such a surface. However, once the patinuer (an artisan who applies the finish) begins, the metal comes alive with color. The subtle detail takes form. Colors enhance the contrasting shadows and a new richness takes shape.

This is the beauty of copper and copper alloys. Its thermodynamic character offers a stability that welcomes the arrival of new elements. While its ductile nature encourages the creation of surprising textures.

A darkened statuary finish can also give copper alloys a deep, old bronze appearance. The term “statuary bronze” is associated with this type of finish. The Bowdoin Museum of Art features Zahner-fabricated naval brass with a custom bronze patina.

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Bowdoin Museum of Art

The new building entrance resembles a glass box on three sides, with the remaining portion clad in a Zahner fabricated naval brass with a custom bronze patina. The patinated metal panels continue from the exterior to the interior angled soffit, completing a dramatic entry for the museum’s 19th Century collection.

Several other color variations are available in the statuary finish category. One that has found use on several architectural surfaces is the premium Zahner finish, Dirty Penny™. We’ll explore this preweathered copper patina surface in the next installment of this series.

Red Patinas

Red is the color of cuprous oxide, so one would think this would be a common and achievable color. However, it is a difficult color to produce in copper alloys. This complex patina has questionable stability unless the metal is coated and sealed from the environment.

The red finish, when achieved, is rich and beautiful. It will change over time and darken, in sometimes beautiful ways, if not protected with a clear coating.

Additional Patina Colors, Hot and Cold

Colors produced by patinating copper alloys are dependent on the chemicals used (to cause the reaction) and the makeup of the metal at the surface. You can use the same chemistry, temperature, and humidity on two different alloys with two different results.

One can see the various color possibilities and patina characteristics in the following chart:

There are two distinct categories of patination processes: the cold application and the hot application. The cold application process is popular on wrought forms of copper, such as sheet and plate, and can be layered to create different effects.

A cold patina process created the beautiful surfaces on the Smithsonian’s National Museum of the American Indian art wall. The layering method was applied to create a mosaic effect.

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The Smithsonian NMAI

The architectural design process included a number of designers and artists, including artist Ramona Sakiestewa, architects Jones & Jones with SmithGroup, and exhibition designers at Gerald Hilferty.

The hot application process is predominantly used on castings and sculpture due to the potential for warping thinner plates and the ability of thick castings to distribute the heat from the process.

As with the cold patina process, the solutions may be layered as the surface reheats. In the hands of an expert, stippling effects and other artistic techniques can significantly enhance the cast sculpture.

In both processes there is a consistency in how the surface is prepared. A clean surface free of all oils, soil, and water is critical for a successful patina to develop. Starting with a clean surface can often be one of the more difficult steps in the patination process.

Contemporary Advances in Copper Textures

From earliest times during the discovery of copper, the ability to hammer the metal into shapes and forms was one of the most endearing properties of this special rock. Artistic surface techniques first used by early craftsmen have transformed via modern methods of imparting designs into the malleable surface of copper alloys with startling results.

Recall the interior walls of the Miu Miu Aoyama mentioned earlier in this post. The copper bullnose details, with dense custom perforations and round zig-zag seams, produce breathtaking depth and beauty.

Repoussé and chasing: The French term “repoussé” means pushing up or out and refers to raising the metal by hammering on the reverse side. “Chasing” is based on the French term chasser, which means to drive or push out. Both are often performed on the same metal sheet to create intricate detail.

Hammered Texture: A step away from the artistic repoussé that utilizes the softness of copper. The metal can be heated and hammered into forms or shapes without ripping or tearing along edges, then oxidized to develop beautiful tonal effects no other material can match.

Embossing: The process of running sheets or coils of thin copper alloy through engraved patterning rolls, which impart the patterns into the copper alloy. Wood grain, leather, and stucco patterns are just a few patterns chosen. An added benefit is that the texture stiffens the copper surface while concealing minor flaws.

CNC Texturing

With the advent of CNC equipment, the ability to shape and form copper alloys has advanced in unique ways. One-of-a-kind textural surfaces are introduced into copper and copper alloy surfaces as remarkable shapes take form.

Other metals can be shaped in a similar fashion, but copper and many of its alloys do not develop excessive local stresses that can warp the surface.

Larger textures are also possible using this equipment. These macro forms in the metal produce shadowing effects that will oxidize at different rates depending on how the condensation remains on the surface.

The surface of the de Young museum’s copper walls illustrates this technique. Here, a series of nine different cone-shaped indentations were pushed inward or outward from the plane of a sheet to develop subtle contrast on the museum’s exterior walls.

This copper facade will, over time, transition from bright golden red to dark brown to black (eventually emerging into earthy greens).

Etching and Engraving

Copper and copper alloys can be etched or engraved to produce extensive surface detail. In both processes, the material is selectively removed.

Etching involves the localized chemical dissolution of the metal and usually necessitates the application of a resist to the surface of the metal not to be dissolved.

Engraving removes metal by mechanical means. Selective abrading, machining, waterjet, and laser cutting can engrave the metal’s surface. Fine machining and control of the tool are critical.

During the impressive entrance portal construction for the Museum of the Bible commissioned by artist Larry Kirkland, vertical lines were etched into the thick brass panels. This design choice nods to the original lines produced from individual type blocks used in Gutenberg’s printing technique.

The Future of Copper in Art and Architecture

From the early dawn of the copper age to contemporary life, the ingenuity this metal has produced is astounding. Copper’s high ductility, combined with the seemingly endless potential of its alloys, project it favorably into the next century.

Awareness is building in the field of sustainability and the unique challenges we face moving forward. As our world evolves, so do the materials we work with. A timely understanding of the current experiments and groundbreaking developments is vital when working with copper in art and architecture.

NEXT: Dirty Penny™: Zahner’s Premium Copper Patina Surface With Iridescent Appeal

In our next installment of this series, we’ll explore the stunning architectural surface designed to transform over time.

Read Part 3 in our series: Dirty Penny™: Zahner’s Premium Copper Patina Surface—Coming Soon!