Choice of Steel = Change of Scale: Nancy Selvage

When artist Nancy Selvage needed perforated stainless steel to make Water Wall, a new public art project at Trolley Square in North Cambridge, she was faced with an array of possibilities. There are over 150 types of stainless steel, with 15 of those types in common use.

Differentiating between types of stainless steel and then selecting the “best” one can be complicated for the artist, partly because the U.S. steel industry employs three naming systems. The most common naming system is the one used by ASTM/AISI (American Society of Testing Materials/American Iron and Steel Institute). Choice of steel is not necessarily “worst to best”. An artist must select the alloy most suitable for both her/his vision and for the environment in which the artwork will be installed.

What Is Stainless Steel?

Stainless steel is a ferrous (iron) alloy with at least 10.5% chromium content, with the most common stainless, the AISI “300” series, containing a minimum of 16% chromium. Chromium gives steel hardness and corrosion resistance. The addition of nickel to the alloy increases corrosion resistance by strengthening the surface layer and causes the molecular structure of the steel to become austenitic, a metallic solid solution state that distinguishes it crystallographically. In this state, the alloy becomes non-magnetic, explaining why certain steels do not respond to a magnet (feel free to try a magnet on the steel samples). The addition of molybdenum further increases chemical stability, particularly protecting the metal from corrosion caused by chlorides (salt).

Making the Choice

Nancy’s fabricators guided her to two excellent stainless steel choices: 304 and 316L (the “L” stands for low-carbon content and is a better choice for welding). Nancy wanted the sculpture to remain bright, reflect light, and be free of corrosion. She considered the qualities of 304 and 316L:

“Since my prior work in perforated metal had been fabricated in aluminum, which works well for indoor and temporary exterior work, I had to rely on professional advice when deciding which grade of stainless steel to use for my work at Trolley Square. After consulting with several metal fabricators, I learned that the 316L alloy would be most resistant to weathering but that the "next best" 304 alloy was also an option. I was tempted to choose the 304 alloy, since using the higher priced 316L would require considerable design adjustments to stay within the budget. Lillian Hsu, CAC Public Art Director, arranged for me to consult with Rika Smith McNally, Conservator of Objects and Sculpture, who recommended I use the 316L stainless steel alloy to best balance the need to have the artwork thrive at the site and my long-term visual expectations for this sculpture.”

With the nearby ocean and road salt spray from snow plowing, 316L was the better choice for Water Wall. To fit within the budget of the project, Nancy chose to use the grade of stainless steel that resists chloride salts, and make the sculpture smaller.

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