How to Use Plaster of Paris for Aluminum Casting

Written by alex smith
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How to Use Plaster of Paris for Aluminum Casting
This statue was created with the Lost Wax Method, which is still used today. (statue image by dani kreienbühl from Fotolia.com)

Metal casting is an art that has existed for thousands of years. Sculptors seeking to create a metal sculpture would first carve the form out of wax, and then make a plaster mould. The wax was melted out and molten metal was poured in, replacing the wax. Once the mould was broken away the sculptor could refine and finish the statue. This process is called the Lost Wax Method, and is still used by artists today.

Skill level:
Moderately Challenging

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Things you need

  • Wax block
  • Sculpting tools
  • Wax rods
  • Lighter
  • Plaster of Paris
  • Bucket
  • Heat gun
  • Metalworking furnace
  • Crucible
  • Aluminium slugs
  • Protective gloves
  • Tongs
  • Hammer
  • Grinder

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Instructions

  1. 1

    Carve the object to be moulded out of a block of wax. You can use sculpting tools purchased at any hobby shop to accomplish this.

  2. 2

    Add a few wax spouts to the object, using wax rods fused to the object by melting their tips with a lighter. One should be slightly larger for pouring in the aluminium, while the others can be more delicate; they are for air to escape the mould.

  3. 3

    Mix a bucket of Plaster of Paris, following the instructions on the package.

  4. 4

    Submerge the wax object into the plaster, holding onto the thick spout. Hold it centred in the plaster -- with the spouts extending out of the plaster's surface -- until the plaster hardens.

  5. 5

    Let the plaster dry overnight to remove most of the water, and then remove it from the bucket.

  6. 6

    Heat the plaster mould with a heat gun to melt the wax. Pour the wax out of the mould periodically. Continue this until all of the wax has been melted out, leaving a void in the shape of your object.

  7. 7

    Place a metal crucible in a casting furnace with a supply of aluminium slugs inside of it.

  8. 8

    Heat the crucible to around 760 degrees Celsius until the aluminium melts.

  9. 9

    Remove the crucible from the furnace with tongs once the aluminium has melted. If there is slag or other impurities floating at the top, scrape off with a stick.

  10. 10

    Pour the aluminium into the mould's pour spout. Keep pouring until aluminium leaks out of all air-escape spouts.

  11. 11

    Allow the aluminium to cool and harden for several hours.

  12. 12

    Break off the plaster mould with a hammer.

  13. 13

    Cut and grind the aluminium spouts off the cast. They can be melted down again for future castings.

Tips and warnings

  • Wear protective gloves when melting the aluminium.

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