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Max-Cast, Inc.
P.O. Box 662
Kalona, Iowa 52247

tel: 1-8_00-728-933_9
local: (319) 65_6-5365
M-F, 8:30am-5:00pm

Metals for Casting

Bronze
Bronze is the classic metal of choice for most sculpture. It is easy to cast, malleable, takes a beautiful polish and a great variety of colored patinas. Most foundries use silicon bronzes containing no lead. In general, they are stronger and offer greater corrosion resistance than traditional tin bronze alloys. Silicon brass alloys are available when a yellower color is desired.

The natural color of bronze is hard to define. As the castings are broken from their molds, they are covered with fire scale and other oxides making them look as though they were freshly dredged from the sea floor. Sand blasting leaves them a light straw color. This slightly roughened surface gives sufficient tooth for chemical treatment with various acids and chemicals to bite into the surface. Textured areas generally keep a stronger flavor of the patina and afford greater contrast if they are buffed.

Polished bronze is brilliant and attractive, but expensive due to the extra time needed to perfect the surface. If polished sections are planned be sure to have your pattern's surface as smooth as possible before the molding process begins. This will head-off snow balling cost overruns. Polished bronze will tarnish unless protected with some sort of clear coat. Unfortunately, no coating will last as long as the polished bronze. You will have to count on removing scuffed, peeled or oxidized coatings and reapplying them from time to time. The artist might consider electroplating portions of the sculpture.

It is very uncommon to pour a large sculpture in one piece. They are usually done in sections. Certain parts of a large figurative piece, for example: head, hands, and feet may be cast using the lost wax method, while the rest of the figure can be done in sand molds, saving considerable time and money.

When additional support is needed for very large works, an internal stainless steel armature may be welded into the sculpture as it is assembled.
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Aluminum and Iron
Where weight and cost are major considerations, aluminum weighs about one third as much as bronze at about half the cost per pound. Large wall-mounted reliefs are often cast in aluminum since they require less structural support.

While it is softer than bronze, cast aluminum tends to be brittle. Thin sections could break under severe stress. It is also rather difficult to weld.

Paint is the usual surface treatment for aluminum castings, but highlights may be sanded and buffed to accent the surface texture. Anodizing can be done on some aluminum although cast aluminum is not the best for it. Outside, aluminum can form white oxides if not clear-coated for protection.

Another phenomenon to be aware of is electrolysis. Joined, dissimilar metals in the presence of an electrolyte such as salty water will act like a battery generating tiny amounts of electricity while slowly dissolving one of the two metals. For this reason stainless steel pins or bolts are often used to secure outside installations since stainless steel is particularly non-reactive.

Cast iron is even more economical than aluminum and may be the most historically correct in some applications. During the nineteenth century, finely detailed, intricate iron castings were as ubiquitous as plastic is today. Of late, iron has enjoyed a rebirth as a sculpture medium. It is superior to bronze in castibililty, since it runs further and picks up greater detail. In corrosion resistance it is a near equal. People often confuse iron and steel. Generally, steel flakes away as it rusts. Iron does not. However, iron does present design limitations. Like aluminum, it tends to be brittle in thin sections and does not weld especially well. Plan for mechanical joints and beefier section thickness especially if the piece may be subjected to any physical abuse.

The sculptor saves by thinking and planning ahead. Realize that the model may need to be cut into sections either for rubber molding or use as a pattern for direct sand molding. Facilitating this saves the foundry time and the artist money. To ensure the various processes continue smoothly, efficiently, and on time, the artist must provide the foundry with all necessary information about the final product at the beginning in the contract stage: wax inspection, metal alloy, base and mounting instructions, surface finish patination (refer to our color patina sheet), edition number, signature and positioning of work (where is the chin in relation to the big toe on the right foot? for example).
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