Aluminum Finishes in Postwar Architecture

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By Thomas C. Jester

The twentieth century witnessed an explosion of new materials and assemblies for construction. Avant-garde architects who subscribed to the tenets of Modernism embraced reinforced concrete and glass to create remarkable new buildings. If concrete and glass were the first two critical material legs of the stool for Modern architecture, metals were the important third leg.

The material qualities of building facades, in particular, relied heavily on metals as the relationship between structure and skin evolved in the period after World War II. Industrial materials and assemblies with a wide array of finishes and standard, known properties became the designer’s palette. Architects in the Modern era selected metals with finishes that produced a wide range of patterns, textures, and colors. Metals were selected not only because they met specific performance criteria and characteristics but also because they conveyed newness, celebrated industrialization, and even highlighted their specific qualities for poetic effect.

The development to Modern architecture was made possible, in part, through the substitution of lightweight for heavy materials, and the use of metals was one of the keys that made the changes possible. In 1947 the frontispiece to the Architectural Metal Handbook, published by the National Association of Ornamental Metal Manufacturers, declared, “Freedom of expression is the cornerstone of progress in architecture. The metals of old, supplemented by the alloys of today, provide the strength, utility and permanence, dignity and beauty to make possible that freedom.” This statement signaled acceptance of the growing impact of aluminum alloys in the building industry by Modern architects in place of more traditional metals, such as bronzes and nickel silver, which had been used widely through the 1930s. Lightweight metals saved time, space, and weight. Architect Eero Saarinen observed that “from the miraculous potentials of engineering and science will come new materials, new possibilities and new problems. These will have to be absorbed.” This was particularly true for aluminum.

Aluminum could be cast, forged, and extruded to create countless types of architectural elements. Aluminum’s ascendency was swift, as the material became more affordable. By the late 1930s the Aluminum Company of American (Alcoa) was producing residential and commercial aluminum windows, which began competing with wood and steel windows and rapidly eclipsed them. Alcoa’s 1938 product literature stated, “Natural aluminum is striking in appearance yet neutral in effect.” Early storefront systems made with solid copper gave way to aluminum, and by 1937 it was estimated that 75 percent of Kawneer’s product line was aluminum.

The rapid proliferation of aluminum building products accelerated in the postwar period, partly due to cost but also because of the shift to the growing number of alloys marketed annually. By 1954 manufacturers adopted standard designations created by the Aluminum Association for the voluminous number of wrought alloys. The new Aluminum Association designations permitted new alloys to be assigned a unique designation once accepted as a standardized metal with known properties.

Experimentation and Postwar Expansion

Architects frequently experimented with metal materials. One of the most striking early examples of aluminum used for a Modernist design was the Aluminaire House, designed by Lawrence Kocher and Albert Frey. Constructed in 1931 for the Allied Arts and Building Products Exposition in New York City, the building was partially subsidized by Alcoa, which provided the aluminum components, including the corrugated panels. During World War II, Vultee Aircraft hired Henry Dreyfuss and Edward Larrabee Barnes to design prefabricated metal housing using 18-foot-long-by-8-foot-tall aluminum sheets bonded to a cellular core, but the prototypes were never mass produced. Buckminster Fuller’s Dymaxion House was noteworthy for its experimentation with lightweight aluminum alloys that had high strength-to-weight ratios. Fuller’s prototypes — designed between 1941 and 1946 and built in 1947 — reflected the passion of its innovative designer.

Following World War II, the largest aluminum producers — Alcoa, Reynolds, and Kaiser — pursued new markets to absorb their increased wartime production capacity, and the building industry was targeted with aggressive marketing through publications, demonstration houses, and award programs. The widespread availability of aluminum in the late 1940s and early 1950s also coincided with the rapid arrival of another important building assembly: the curtain wall. Pietro Belluschi’s Equitable Savings and Loan Building in Portland, Oregon, constructed in 1948, featured prefabricated cast- and sheet-aluminum panels in a contrasting configuration to emphasize the reinforced-concrete structure. On a larger scale, the 30-story Alcoa Building in Pittsburgh, Pennsylvania, designed by Harrison and Abramovitz and completed in 1953, was widely publicized as a “daring expression of the metal curtain wall.” In contrast to the mostly-glass curtain wall of the early 1950s, the Alcoa Building’s curtain wall, a so-called “Aluminum Dress,” was formed with large 6-foot-by-12-foot stamped anodized panels of “iridescent gray color” (Fig. 1).

 Fig. 1. Alcoa Building, curtain wall detail, Aluminum on the Skyline, published by the Aluminum Company of America, ca. 1954.

Metals also were often used in the growing number of composite materials that took advantage of the properties of more than one material to make lighter, stronger materials. In 1947 Steel Magazine would declare that “composite material is the Janus of many of today’s cleverly engineered lighter structures.” One of the early composite materials using metal was the Haskelite Manufacturing Company’s Plymetyl. Light-gauge metals — zinc-coated steel, aluminum, Monel, stainless steel, and porcelain enamel — were bonded with phenolic resin to plywood or insulating board. Composite sandwich construction would grow rapidly in the postwar period, particularly for curtain-wall assemblies. The curtain-wall assembly for General Motors Technical Center in Warren, Michigan, designed by Eero Saarinen in 1950, was a 2-inch-thick composite panel of porcelain enamel on aluminum, laminated to a paper honeycomb core.

In 1940 Buffalo-based Rigidized Metal Company introduced deep-textured sheet metals for architectural applications in both ferrous and non-ferrous metals, including aluminum. Formed by rolling, the embossed Rigid-Tex sheets came in a wide range of patterns and varying pattern depths. Promoted for its increased tensile strength and elimination of any distorted surface reflections (oil canning), the products gained widespread acceptance in exterior and interior uses, ranging from curtain-wall panels to elevator cabs.

Postwar Aluminum Uses and Finishes

Stainless steel and aluminum dominated as the metals of choice for architects during and after World War II and into the early 1950s. As the number of finishes for stainless steel and aluminum grew, they provided architects with more choices than ever before. For Mies Van der Rohe, materials were to be used for structure or enclosure, and he believed materials should be used based on research and facts. He commented in 1956 that “the danger with aluminum is that you can do with it what you like; that it has no real limitations.” But Mies’ warnings would not stop the major three aluminum producers from flooding the market with an ever-growing array of aluminum components, including windows, doors, siding, roofing, storefronts, curtain walls, sun-control devices, flashing, railings, copings, and acoustical ceiling assemblies, not to mention structural components. Aluminum quickly became ubiquitous in buildings, partly because it had become economical but also because of the aluminum industry’s marketing prowess.

Types of Aluminum Finish

Finishes for aluminum fall into three categories: mechanical, inorganic, and organic. Typical mechanical finishes, achieved with brushes or abrasives to impart texture and contrast, ranged from satin, sand burnished, polished, sand blasted, and spin finished to frosted. Inorganic finishes on aluminum could be created with chemicals, chemical oxidation, electrochemical treatment (anodizing), electroplating (metal fused to aluminum), and porcelain enamel (glass fused to aluminum). Organic finishes include synthetic lacquers, alkyd methacrylate lacquers, and paint.

Anodizing, prized for its corrosion resistance and ability to maintain its original appearance over time, would prove to be the most important aluminum finish. Alcoa first patented its color-anodizing process in 1923 and by 1928 was commercially producing anodized aluminum under its Alumilite trade name. Advances in processes and techniques for anodizing aluminum played an important part in its widespread use in buildings. The anodizing process created a thin, protective film of aluminum oxide that could be clear or colored.

In 1938 Alcoa noted in its product literature that its Alumilite finish was “proving useful for architectural parts such as storefronts which must resist atmospheric attack for prolonged periods, and still present a pleasing white appearance.” Reflecting the fact that anodized aluminum remained somewhat of a novelty well into the 1950s, the Reynolds Metal Company devoted an entire section of its 1958 supplement to Aluminum in Modern Architecture to the benefits of anodizing. It declared:

Aluminum, electricity, and chemistry — the three elements of anodizing — are all relatively recent developments of man’s continuing long search for better things.

Not only did aluminum offer the benefit of its strength-to-weight ratio: it had other possibilities that would interest architects, including color.

Postwar Metals and Color

The prolific use of white metals in the 1930s gave way to the growing use of stainless steel and aluminum in the 1940s by architects as Modernism took hold in the United States. Color was often associated with ornament, and the immediate postwar period relied largely on a palette of materials with “natural” color (in contrast to those deemed artificial). High-style Modernists favored “a somewhat elastic range of materials: travertine, marble, wood, leather, glass, steel, and aluminum, each in their variety of finishes.”

Interest in color grew as Modern architecture morphed away from the perceived monotony of the glass-and-metal boxes of the immediate postwar period and as Modernism became more mainstreamed for the masses. Taking into account the inherently disruptive and transformative nature of scientific advances that led to new materials, manufacturers sought to expand their reach in the architectural market by offering new metal products with a variety of textures, patterns, and colors. Architect Victor Gruen argued in 1958 that “if applied with judgment, taste, and imagination, colored aluminum opens tremendous new possibilities in liberating our urban environment from the dreariness created by the exclusive use of the somber, ‘safe’ colors,’” which he considered to be black, white, and gray.

Throughout the 1950s interest in color expanded, and manufacturers responded to give architects more choices when designing with metals. In 1957 Alcoa’s newly created Residential Building Products Division hired Modernist architect Charles Goodman to design its “Care-Free” home (Fig. 2). The constructed houses, numbering fewer than 50 nationwide, featured color-anodized aluminum (purple for the siding and blue for the window grilles) and were advertisements for how aluminum could be used in residential construction. This program reflected not only the desire of aluminum manufacturers to expand their reach into the residential marketplace but also the growing shift toward acceptance of color in Modern architecture, as fashions changed and shifted away from the natural colors supported by first generation, high-style promulgators of Modernism to brighter possibilities.

 Fig. 2. Cover of Alcoa Care-Free Home, published by the Aluminum Company of America, ca. 1958. The exterior featured anodized aluminum components including purple siding panels and iridescent blue lattice work in front of the floor-to-ceiling windows.

Color-anodizing technology. Until the early 1950s the only colors available for exterior applications of anodized aluminum were transparent finishes and variations of silver. Black, grey, and green colors could be achieved with chemical conversion processes, such as chromatizing and phosphatizing, which were most commonly used as a primer for painted finishes. Polished finishes on aluminum could be achieved with chemical polishing. While some colors of anodized aluminum could be specified safely for interior use, colors for exterior use were limited, due to the UV degradation of some color media over time with exposure to sunlight. The UV stability depended upon the stability of the coloring media, the concentration in the oxide layer, and the depth of penetration.

Despite the limitations in durability, the Reynolds Metal Company recognized the potential of color, noting that “the metallic luster of colored anodic films has great decorative attraction,” and devoted considerable energy after World War II to improving various methods for color dyeing anodized aluminum. By the late 1950s manufacturers were beginning to produce a wider color range for anodized aluminum, and they continued to experiment with materials and processes that might lead to commercially viable anodized finishes with an even wider range of colors while maintaining the benefits of the protective oxide layer afforded by the electrochemical finishing process.

A wider range of colors became available only with improvements in the process to seal UV-stable coloring media in the oxide film of the metal at the end of the anodizing process. Corrosion inhibitors could be added when maximum corrosion resistance was desired. Additional protection was afforded by the application of a coating of clear lacquer baked on the anodized metal.

Anodic films could be colored in one of three ways. Organic, water-soluble dyestuffs and inorganic pigments were used to create various colors. In this method, anodized components were dipped directly into a dye bath and absorbed the color. Colors could also be created by treating the natural oxide film with solutions that formed inorganic colored compounds. This method could create black and blue colors. In a second method, film in such colors as silvers and browns could be achieved directly in the anodizing bath with the addition of acids and other agents. Variations in the alloys also influenced the color of the anodic coating. Chromium, for example, produced a yellowish tint, and manganese created brown hues. Finally, manipulation of the metal with mechanical and chemical treatments prior to anodizing also created varying color shades and the potential for contrast. Rougher surfaces tended to appear darker after application of the Alumilite finish, making color matching of different anodized elements difficult.

By 1956 colors suitable for exterior use included blue, yellow, black, and gold, in addition to the clear (transparent) and gray finishes. Architect Minoru Yamasaki embraced the potential of colored aluminum, stating, “Anything that increases our palette is wonderful, and if and when colored aluminum becomes absolutely a permanent thing, I think it opens up a great many fields.” His 1958 design for the Reynolds Great Lakes Sales Region Headquarters Building in Southfield, Michigan, incorporated gold, silver, and black anodized aluminum and was a widely published billboard for color-anodized aluminum (Fig. 3).

 Fig. 3. Reynolds Great Lakes Regional Sales Center, Southfield, Michigan, 1958. Photograph by Balthazar Korab, courtesy of The Library of Congress

The rise of earth-toned anodized finishes. The wider use of colored metals in the 1950s and early 1960s eventually shifted to a more natural color palette in late 1960s and 1970s. Earth-tone colors on anodized aluminum replaced brighter colors, and clear anodized aluminum and stainless steel were used with less frequency. As earth-toned materials, such as cast-in-place and pre-cast concrete, brick, and stone, gained prominence during the second half of the 1960s, champagne and light bronze anodized finishes, as well as medium bronze, dark bronze, and black anodized finishes, were used extensively to compliment the more natural tones in the cladding materials. This trend would continue well into the 1970s.

Darker, earth-toned aluminum colors also complimented buildings constructed with other metals used in the late Modern period, including weathering steel and copper-based alloys, such as bronzes, brasses, and Muntz metal. Architects also used dark bronze anodized elements, such as spandrel panels, to contrast with lighter-colored aluminum elements, like curtain-wall mullions.

The predominance of the earth-toned colors of anodized aluminum may also be explained by the evolution and maturation of anodizing technology. Colors in the brown and bronze range could be created using materials and techniques that produced finishes with the greatest amount of resistance to UV-light degradation in exterior applications. Manufacturers continued to search for improved manufacturing processes that provided superior performance of color–anodized aluminum. Around 1985 electrolytically deposited anodic coatings were introduced. This process is widely used for exterior architectural applications requiring significant UV stability.

Conclusion

Today, as Modern-era buildings require renewal with ever growing frequency, it is important to understand the range and complexity of materials used. The postwar period was one of rapid change in the materials and metal finishes available, and the legacy of architectural production is equally rich and varied. For this reason, a strong understanding of the alloys used and how the finishes were created is essential when evaluating aluminum’s condition and in developing sensitive and appropriate repair and conservation programs.


About

Thomas C. Jester, AIA, FAPT, LEED AP, is a Principal at Quinn Evans Architects. This article is excerpted from the full version published in the 46:1 issue of the APT Bulletin, the Journal of the Association for Preservation Technology International.