Sculptures and Drawings
by Olivier Duhamel

A brief overview of the ceramic shell and lost wax techniques for bronze casting.
 

1 Ceramic shell and lost wax principles for bronze casting.

1 Make a wax replica of the sculpture
2 Build a thin ceramic shell around the wax.
3 Melt the wax out of the shell to make an empty cavity.
4 Pour the molten metal into the shell.
5 Break the shell to free the bronze sculpture.


2 Making the original sculpture.
- Clay.
- Plasticine.
- Wax.
- Anything else…

3 Making the mold for wax replica.
- Silicon rubber skin.
- Plaster support.

4 Making the wax replica.
- Pour liquid wax (110 Celsius) into the mold.
- Solid wax for solid bronze: fill the mold
- or hollow wax for hollow bronze: a thin layer of wax.
- Careful! no air bubbles!

5 Cleaning the wax.
- Fill bubble holes.
- Smooth out seam lines.

6 “Sprueing”
- finish the wax structure by adding:
- Feeding channels.
- Pouring cup.
- Vents.
- For hollow wax fill the inside of the wax with a “core” refractory plaster

7 Building the shell.
- Mix a creamy “slurry” of Molochite flour (Calcinated Kaolin) and Colloidal Silica.
- Cover the wax structure with 5 layers of slurry + backup Molochite sand.
- Let each layer dry before applying the next one.

Shells drying - a fan helps.

8 “dewaxing”
- Very hot flame.
- Wax burns and melts out of the shell leaving an empty cavity.
- Beware of cracks (hot wax expands before melting but ceramic is not flexible.)

9 Reinforcing the shell.
- With a thick slurry:
- Fix cracks.
- add fiberglass.

Jill reinforcing shells

10 Baking the shell.
- Red hot at 600 celsius for 20 minutes in the baking furnace will harden the shell
- Set the shell upside down on a bed of dry sand reading to receive molten metal.

11 Melting the metal.
- We use Silicon Bronze (Herculoy 92% copper, 4% Silicon, 4% Zinc or Everdur 95% Cu, 4%Si, 1%Mn)
- A basic LPG furnace: fire bricks and refractory blanket
- or a purpose build refractory cement furnace for “coke”
- Silicon Bronze melts at 980 Celsius (20 minutes)
- Pour temperature: 1000 to 1200 Celcius.

12 Pouring the metal.
- Wear protective clothing
- Scoop out slag before pouring.
- Don’t drop the crucible!
- Pour quickly but gently. (no turbulences)
- Have a nice cold beer.

13 Breaking the shell.
- Let the shell cool 20 minutes.
- Hammer, chisel out the ceramic shell to reveal the bronze cast.
- Inspect the cast for defects (fins, miscast, shrinkage, porosity, inclusions, bubbles, holes etc…)
- Too many defects? remelt.

14 “Chasing”
- Cutting off “sprues” and vents.
- Grind back to shape.
- fix defects.
- Brazing, welding.
- File, sand, polish.

15 Patina.
- Oxidation of the metal surface.
- Potassium sulfate.
- Cupric nitrate.
- Ferric chloride.
- many others…
- Mix, layer, highlight
- Seal, wax and shine

16 Finishing
- Mounting (Wood, Granite, Marble, anything else…
- Take photographs.
- Publish on web site.
- Print and sign certificate of authenticity.

All done ? .. Not quite…

17 …sell the sculpture
Art galleries
Art fairs
Exhibitions
Auctions
Studio Open days
Online
Word of mouth.

 
 

Contact

Olivier@Duhamel.bz

 

How a bronze is made

Read the manual written by Jill Varani

 

Le Bronze c'est quoi?

Lisez une mine d'information compilee par le Bazaar du Luxe.

© Copyright Olivier Duhamel 2003-2009