The Writer’s Guide to Casting Metal
While blacksmithing may be the most well-known method of shaping metal, casting is a craft just as ancient. Casting can also produce intricate shapes that a blacksmith cannot match. Casting is commonly represented in fiction, especially in the “gearing up” scenes, although many of those scenes are inaccurate.
As always, magic is the exception to the rule. Because magic.
History
As I mentioned in my Writer’s Deep Dive: Metalworkers, the oldest cast piece is a copper frog from 3200 BC, that was found in Mesopotamia. [1] However, it is believed that the origins of metal casting are rooted in Southern Asia, specifically China, India, and Pakistan. [2] Most of these early pieces were tools, weapons, and religious statues.
Ancient people commonly added lead when casting copper because it made the molten copper more fluid, allowing them to cast more intricate designs. An example is the dancing girl statue from Mohenjo-daro. [3]
India was the first to use casting to mass produce coins, starting with silver but switching to copper alloy. They stacked multiple coin template molds in a clay cylinder and poured molten metal down the center. This method produced one hundred coins at once. [3]
Types of Casting
Lost Wax Casting – This method is used to create a replica. A mold is made from the original and from the mold, a wax or paraffin cast is made. The wax is covered in a fireproof material such as clay, then heated upside down so that the wax runs out or is “lost.” Then the remaining clay mold is filled with molten metal. The original object can either be a carved wax model or a finished piece, such as a metal statue.
This method of casting is one of the most ancient. The oldest examples of lost wax casting are gold artifacts that were found in Bulgaria. [4] A record was found on a clay tablet in Sparta, Babylon that specified how much wax was needed to cast a key. [5] This technique was adopted early in the Middle East and West Africa. China and Western Europe adopted the method much later. [3]
Mold Casting – Also known as molding, this process involves pouring molten metal into a rigid mold. Early molds were made of stone or ceramic. Articulated molds had multiple pieces that assembled to form a complete mold. [6] One method, known as piece-molding, used different molds to create separate pieces that were joined. Larger pieces such as statues were cast in pieces rather than the whole being cast at once.
Writer’s Tip: It has become common to see mold casting used to create swords in many fantasy movies and TV shows. However, mold casting is not a suitable method for creating a sword. Forging and tempering produce much better blades. Casting can produce good quality spearheads.
Sand Casting – A form of mold casting, this method uses an impression made in sand as the mold rather than a carved stone or molded ceramic mold. The sand is commonly mixed with clay to help it hold its shape. Molds made of sand are cheap, but they wear out faster than a stone or ceramic mold and also cannot produce the fine detail that other methods can.
Plaster Casting – This method is like sand casting but uses plaster instead of sand for the molding material. It can only be used with non-ferrous materials. The metal cools more slowly with this method than with sand casting, allowing time for the metal to fill thin cross-sections, creating more complex and detailed parts. [7]
Other Methods – There are more modern methods of casting that I have not covered. I choose to highlight those used during the ancient and medieval periods. Other methods include die casting, centrifugal casting, investment casting, rapid casting, and squeeze casting.
Finishing
Once the raw castings are released from the mold, they must be finished. The primary work is removing the unwanted extra metal, which includes the access port through which the metal was poured. This process is known as fettling and is often time-consuming. [8] After that, the piece is smoothed with filing or grinding and assembled, if it has multiple parts.
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Copyright © 2022 Rebecca Shedd. All rights reserved.
[1] Ravi, B. (2005), Metal Casting: Computer-Aided Design and Analysis (1st ed.), PHI, ISBN 81-203-2726-8 [2] Davey, Christopher J. (2009). J. Mei; Th. Rehren (eds.). The early history of lost-wax casting. Metallurgy and Civilisation: Eurasia and Beyond. London. pp. 147–154. [3] Craddock, Paul T (October 8, 2014). “The Metal Casting Traditions of South Asia: Continuity and Innovation”. Indian Journal of History of Science. 50 (1): 55–82. [4] Leusch, Verena; Armbruster, Barbara; Pernicka, Ernst; Slavčev, Vladimir (2015-02-01). "On the Invention of Gold Metallurgy: The Gold Objects from the Varna I Cemetery (Bulgaria)—Technological Consequence and Inventive Creativity". Cambridge Archaeological Journal. 25 (1): 353–376. doi:10.1017/S0959774314001140. ISSN 0959-7743. S2CID 163291835. [5] Hunt, L. B. (1980). The Long History of Lost Wax Casting, Gold Bulletin. p. 66-79. [6] “Articulated mold assembly and method of use thereof”. google.com. 14 March 2013. Retrieved 19 March 2018. [7] Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4 [8] T F Waters (11 September 2002). Fundamentals of Manufacturing For Engineers. CRC Press. pp. 17–. ISBN 978-0-203-50018-7.
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