The Reasons Porous Molds Could be Used In Egyptian Casting

The British Museum-Ancient Egyptian Cat

The British Museum-Ancient Egyptian Cat (Photo credit: AKinsey Foto)

English: Liquid bronze at 1200°C is poured int...

English: Liquid bronze at 1200°C is poured into the dried and empty casting mold. (Photo credit: Wikipedia)

English: Melting metal in a ladle for casting ...

English: Melting metal in a ladle for casting Deutsch: Metall wird in einer Gießpfanne zum Schmelzen gebracht. (Photo credit: Wikipedia)

Egyptian bronze art, and many of their swords were made by casting into clay molds. Clay, though, is very porous, and so are many other casting materials used then as well as today. So why doesn’t the molten metal seep into the pores and adhere to the mold itself? Two reasons.

 

One reason is that gases are formed around the molten metal, such as oxygen forming a compound, or some of the molecules superheated into gaseous form, or many other such things that form on or over the surface of the molten metal. Anyway, this gas goes in between the metal and the mold, pushing the metal back in a super-thin layer, so the metal still takes on the details of the mold, without seeping into the pores.

The second reason is that the surface tension of many metals is so great that it will not seep into the pores, and yet still not too much so the metal could flow into the finest of details in the mold.

So when the Egyptians cast their metals, luckily they did not have such great surface tension that would prevent detailed casting, but gold, silver, copper and bronze were all metals that had good surface tension, which kept the metal from seeping into the pores. Also, the tension could keep the metal smooth against the rough mold wall, and so make polishing later on much easier, producing the fine bronze sculptures that are dug up today and found inside the pyramids.

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