Cover: Steel Surfaces by L. William Zahner


Zahner's Architectural Metals Series offers in-depth coverage of metals used in architecture and art today. Metals in architecture are selected for their durability, strength, and resistance to weather. The metals covered in this series are used extensively in the built environments that make up our world and are also finding appeal and fascination to the artist. These heavily illustrated guides offer comprehensive coverage of how each metal is used in creating surfaces for building exteriors, interiors, and art sculpture. This series provides architects, metal fabricators and developers, design professionals, and students in architecture and design programs with a logical framework for the selection and use of metallic building materials. Forthcoming books in Zahner's Architectural Metals Series will include Copper, Brass, and Bronze; Steel; and Zinc surfaces.

Titles in Zahner's Architectural Metals Series include:

  • Stainless Steel Surfaces: A Guide to Alloys, Finishes, Fabrication and Maintenance in Architecture and Art
  • Aluminum Surfaces: A Guide to Alloys, Finishes, Fabrication and Maintenance in Architecture and Art
  • Copper, Brass, and Bronze Surfaces: A Guide to Alloys, Finishes, Fabrication and Maintenance in Architecture and Art
  • Steel Surfaces: A Guide to Alloys, Finishes, Fabrication and Maintenance in Architecture and Art

Steel Surfaces

A Guide to Alloys, Finishes, Fabrication, and Maintenance in Architecture and Art



L. William Zahner






This book is in honor of David Norris. A friend and mentor.


“Know your own value.”

Hank Rearden of Rearden Steel

Atlas Shrugged by Ayn Rand

Steel was one of the first metals I became acquainted with early in my career. It was different than the shiny copper the shop had stacked in a neat pile or the lightweight aluminum stored in racks up off the ground. Steel was heavy, thicker than most other sheet metals, and often possessed the intricate spangle of zinc crystals on the surface from the hot-dip galvanizing process.

Steel was treated rougher. Stored in open stacks. Often coated in a layer of slick oil. It had a smell to it—the smell of machinery, the smell of industry. Steel lacked the care and concern the other metals seemed to be regarded. It was the metal used for making patterns,1 before the shapes would be cut in copper, aluminum, or steel's royal cousin, stainless steel. After which, they would be relegated to the scrap bin to be recycled. We used to recycle all the metals, and on occasion I would take a massive load of steel scrap to the recycling yard, only to receive less than 20 dollars. It hardly seemed worth it, but we were a company that had worked with metals through the hard times of the Depression, and you wasted nothing. Every steel packaging band was collected and recycled.

The first major projects I was involved with out of college had steel siding panels for cladding the walls of large coal-powered electrical generating plants that dotted the Missouri River. These heavy panels were roll-formed from 18-gauge cold-rolled steel sheet made by INRYCO, short for the Inland Ryerson Company, a once massively large steel producer in the United States. Inland Steel Company, founded in 1893, was one of the last integrated steel companies that turned ore into steel and into semifabricated wrought materials. Its subsidiary, Inland Building Systems, merged with Ryerson and later became INRYCO, but eventually felt the impact of foreign sources of steel and modernization and efficiencies of the mini-mills.

These steel-clad powerplants have stood for over 40 years. The paint coatings used on the steel structure and on the steel panels I worked with was of very high quality and today show little signs of deterioration—some fading with time and ultraviolet exposure, but generally the surfaces are in excellent condition.

Over time, my experience moved away from the mild carbon steels of siding and metal decking. Aluminum became the base metal for high-quality paint systems. Stainless steel, copper alloys, and later zinc were the metals for design of exposed, uncoated surfaces.

But there was this other interesting steel, a paradox of metal. It was called Corten.

Here was this strange steel that you wanted the surface to corrode. It would stain everything below it while it formed the initial rust, yet it was supposed to last as long as the stainless steels.

The company built its first major building in 1982, and the designer wanted a natural appearance. He chose Corten siding for the plant portion and alclad aluminum for the office. The siding was roll-formed by INRYCO as one of the last gasps of steel production, as INRYCO was to close its doors in 1986. The architect described his design as the new growing from the old – the old being the rusty metal surface of Corten. It is interesting that over the last 40 years, it is the Corten, the weathering steel, that has embraced the future and still appears sturdy and strong while aluminum is looking fragile and antiquated.

I have worked with weathering steel, the name used as often as the older Corten—or COR-TEN®, as the inventor and trademark holder, US Steel calls it. COR stands for corrosion resistance and TEN stands for tensile strength. Both of these characteristics and more are possessed by this amazing steel.

Nearly 25 years ago we realized the major drawback, from an aesthetic standpoint, was the time it took for the real deep color to appear. People did not want to wait and watch as their building rusted and painted the sidewalks and stonework with a red stain. The idea of preweathering this type of steel seemed to be the answer. Many an artist pushed the metal to achieve this preweathering on their sculpture using acids and wetting the surface. In addition to being hazardous to one's health and safety, this process is impractical for large projects.

After a bit of testing and trials, we came up with a process we now call Solanum, the Latin word for eggplant. The color of eggplant is a deep purple brown, similar to what is achieved when weathering steel reaches its point of surface equilibrium. Solanum sounded fitting for a metal, in tune with the great Sir Humphrey Davy, who named such metals as potassium, sodium, and, of course, aluminum.

The idea with preweathering is to control the oxide development in an environment specifically controlled for this special steel to corrode slowly and form three rich forms of oxide on the surface, similar to, but much quicker than, the color that formed after years of exposure. The staining would be contained for the most part and collected in our plant.

The weathering steels have a rich color tone that comes across as a material of the earth. Like brick, wood, or patina copper, weathering steel has a very natural, pleasing appearance once the oxidation takes root. Many of the projects shown in this book demonstrate the natural character of this amazing steel.

The steels we sometimes refer to as mild steel or carbon steel are ubiquitous in our everyday environment. Unlike the weathering steels, we do not notice them until they do begin to corrode. Otherwise, they go about their business of protecting us as we drive down the road, or hold our buildings up against the forces of gravity and wind. Once they start to corrode, they get noticed like mold on bread. The carbon steels with their beautifully rugged, dark gray-blue color require some form of protection to hold back rust from developing. It is the material of battleships and tanks, armor to be abused and to withstand abuse, but a little moisture and trouble sets in.

More and more designers are seeing the intrinsic beauty of the carbon steels. Conquering, or at least forestalling, the onset of the feeling of neglect the condition of rust can portray is paramount. Iron, the main element in steel, wants to join up with oxygen – and iron has more ways to join with oxygen than we can count on both hands. There are 16 oxide forms of iron. You want to keep the steel surface dry; water is the catalyst for this coupling with oxygen.

Conversion coatings slow down the marriage with oxygen by introducing other elements such as phosphates, sulfates, and copper selenide coatings that cling to the iron surface and form a barrier of darkened color. At the same time, these coatings can offer a unique appearance while maintaining the intrinsic beauty of steel.

Of all the metals I have written about, steel has been one of the more challenging. From an art and architecture perspective, steel has played a valuable role, but as a bit player, it is an inexpensive alternative. With new techniques of preweathering the high-strength, low-alloy (HSLA) steels, this surface is being recognized as a beautiful, natural material by designers and artists around the world. The darkening, bluing, and variegate finish one can obtain from the mild carbon steels adds an entire new array of possibilities to the design community. Easy to work with, weldable, and now with appealing surface finishing, steel is giving new value to the designer and artist.

L. William Zahner


  1. 1   Up until the early 1980s, patterns were made from paper blueprints. There were no CAD–CAM files. Steel patterns would be cut to for later use to make elbows or roof jacks. The patterns were hung from hooks on the wall, and when similar items were made, the patterns would be used on the layout benches. A bit archaic in light of the technology of today.