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Bronze
 

 

                                  
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Casting from Wax to Bronze


                       
        Lost Wax        Ceramic Shell    Abstract Sculpture    Reclining Nude

 

 
Lost-Wax & Ceramic-Shell Processes:  Click Here to see the difference between lost wax and ceramic shell.


"Attending a bronze 'pour' can be an exhilarating experience for any artist or collector. The piece comes alive when the molten bronze is poured into the negative space of the investment (mother mold). Anticipation runs high, because all of the time, cost, and preparation could be for naught, if even one of the steps goes array. Conceiving and setting an artistic design in clay or wax is only 1% of the total time taken to finish a bronze sculpture. The other 99% is just hard work."
Nannette

 
Lost-wax process in 8 steps.
 
 

 

 

1) Affix wax sprues to a wax image. Many sprues are use to ensure that, during the pour, the liquid bronze reaches all areas of the piece. Above, is Balance, in wax; see the finished bronze in the last frame.

2) Make a "mother mold." The wax unit (image and sprues) is placed in a large container that is filled with a mixture of sand and plaster, called investment. This thick coating must harden before going into the kiln.

3) Molds are placed upside-down in the kiln; the kiln's temperature is adjusted and watched for three days, while the melting wax slowly drips out, leaving negative space for the liquid bronze to flow.

4) After 3 days in the kiln, the molds are taken out, turned right-side up, and immediately placed in a sand pit; extra sand is added and packed around each unit, to keep the molds from cracking, during the pour.

 

 

    

 

 

5) The crucible is filled with solid-bronze ingots, that are melted in the green furnace, shown in Step 6. The ingots melt to a hot-liquid.

6) The liquid bronze is slowly poured into each mold, via the hollow openings created when the wax sprews melted, in Step 3.

7) The investment needs to cool, before the sand mixture can be cracked, chipped, and washed away; sprues are cut off the piece, Balance.

    Balance, 1982, 15"x16"x8"
8) The bronze surface is sanded and refined; a patina is applied; sculpture is affixed to its base.
 

 


By 1982, Nannette had produced many small bronze-abstract sculptures and enjoyed sucess using the lost-wax casting process (described above). Her first pieces were 3 to 5 inches tall, making this time-consuming process manageable, and a perfect learning exercise. With Balance, Nannette tripled the measurements, and the work involved was daunting. The complicated sprue network, in Step 1, and the larger investment unit, in Step 2, were challenging.
                                                                     
 
   



Waves
1980, 2.5"x4"x2"


Godiva
1982, 5"x5"x3"

Déjà Vu
1980, 4"x3"x2"

Aerobic
1982, 5"x4"x4"
 

Ceramic-Shell Process

The major difference, between the ceramic-shell and lost-wax processes, is the investment, that creates the mother mold (steps 1, 2 and 3 in lost-wax process). The photo
to the right, finds Nannette preparing her wax sculptures for a ceramic-shell pour in 1988, and illustrates the following:

Step 1: The system of sprues is much less complicated. The investment molds are a simple thin "shell," made of a silicon mixture, covering the sculpture and sprues.
Step 2: The shells are heated with a blow torch, and the wax melts out in minutes, dripping into a receptical. This wax "burn out" creates the needed negative image (the empty spaces in the shape of the sculpture and sprue system) inside the investment shell.
Step 3: The empty-silicon shell is then placed upside-down and put in the kiln on its pouring spout, to allow any excess wax to evaporate, while keeping it warm for the pour.

In contrast, the lost-wax process requires the wax to "burn out" (evaporate) in the kiln for 3 days. The kiln’s temperature builds slowly to 1,200 degrees Fahrenheit. Then the temperature is slowly lowered to keep the investment from cracking.

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