To our dismay it coexists with the "life of the material world" - a serious challenge to many design concepts. Raw materials, processes, and people have real limitations. Ever wonder why a model translated well in fabricated extrusions but looked rather disappointing in cast metal? It is important to know how to take an inspired vision and through an understanding of the materials and processes transform it into an object of admiration.

Sand casting is the type of custom casting most often done by Robinson Iron. This process will not allow for undercutting. Everything on the surface of an object must lift. If you think about it, the same principal holds true for making a sand castle at the beach. Wet sand slips easily out of a tapered plastic cup. The edges of the molded sand have a slight radius because the size of the grains of sands themselves dictates how closely they may be crowded into the corners of the cup's bottom. The water acts as a release agent. Sand casting requires a smoothly formed surface with eased crevices and slightly softened edges.

Cleverly cheated details allow a design to lift from the mold. No groove or flute can exceed one half of its circular diameter while at least two degrees of draft are needed for vertically lifting planes. The same holds true for raised or reeded surfaces. Generally speaking when more complex undercut shapes are absolutely necessary an assembly consisting of multiple castings is required. Most designs may be modified to conceal seams by hiding them under an overhanging edge or along a naturally occurring line within a fold.

A separate pattern must be made for each casting in an assembly. The pattern is used over and over again to create the number of molds to be poured and thus the number of castings. A pattern with too thick a section risks a concentrated build-up of heat in the mold causing a shrinkage defect in the casting. A typical wall thickness is about 3/8" to 1/2". To achieve this desired thickness the design is either relieved on the reverse side or a core is created to form a void within the object. A pattern with very narrow or too few connective elements risks cold shuts or what is commonly referred to as a cold run. A cold run is where the liquid metal cools too rapidly as it runs toward the farthest regions of the mold. If the metal is chilled too quickly the casting will be incomplete. Metals with lower melting temps like aluminum and bronze can more easily form intricately linear lacelike designs. Metals with higher melting temps require a more open design with larger sections. All in all the inherent strength of metal affords the designer a lighter look and more linear design than alternate materials such as stone or terra cotta. When creating a design visualize how the metal will flow through it. Drawing an additional feeder vine or tendril may make the difference in a complete or a partial casting. Providing a deeper border around a design will also create a reservoir of metal to feed an intricate detail.

A carefully modeled rendering should offer information about the surface character of the object. Does the form bulge out or in? Does it transition slowly or plunge abruptly into other shapes. Great changes in plane can seemingly be obtained through visual trickery making the object seem more three dimensional. In your rendering you should have a single strong light source most often located in the upper left hand corner and your strongest dark will nearly always occur at the transition nearest your lightest area. A soft reflected light appearing within the shadowed area on an object will help define the overall form. The background should start in a darker shade behind the lighter side of the object being rendered and transition into a lighter background behind the shadowed side. A cast shadow reinforces the form. A fluidity of form and tactile surface quality will combine to give any rendering life.

Understanding the nature of cast metals and the processes by which they are made is only part of the information required in custom casting. Robinson Iron specializes in the restoration of period metalwork. Historical Restoration requires knowledge of Art History and a familiarity with examples from specific eras. For example in the United States our earliest examples of cast metals are small and finely detailed. They were accent pieces to larger forged assemblies. As technology evolved and entire assemblies made of larger castings were produced the detailing exhibits a broader, bolder interpretation of form. These exuberant sculptural pieces reached their zenith near the end of the nineteenth century just before the birth of modernism.

It is exciting to see a designer really exploit the medium of cast metals. A wealth of expression exists in the beauty of a cast surface. How sad it is to see a minimalist approach that looks good as an extruded fabrication end up looking like so much sanitary pipe. The very last thing a foundry wants is to have a client disappointed in a lovely sand textured surface. Workshops sponsored by organizations like The Institute of Classical Architecture & Classical America are broadening the designer's vocabulary and enriching our built environment. With an understanding of methods, materials and with advances in technology surely any designer can turn dismay into delight.