Lost wax casting

Lost wax or “cire-perdue” casting goes back at least as far as 3,000 B.C.E.  Archaeologists have uncovered evidence of early lost wax casting  on every continent except Australia.

The enduring popularity of the lost wax method is due in part to the fact that it captures very fine detail.  And it can be done without high-tech equipment.

 

Making the model

The rough beginning of the corgi head door knocker

The rough beginning of the corgi head door knocker.

My first step is to carve a model.  For jewelry, I start edwith a wax that’s very similar in hardness and working properties to wood.  Like wood, green jeweler’s wax can be carved with knives and tiny hand tools, or worked with a dremel.  For sculpture, I occasionally use brown microcrystalline sculpture wax, but more often these days I model in plasticine or polymer clay.I start with reference photos and drawings.  I model the rough shape with my hands, supporting it with an armature if needed, then carve details with hand tools. 

 

The corgi head, , a couple of weeks into the sculpture process.

The corgi head, a couple of weeks into the sculpture process.

Clay a very forgiving medium.  If you cut off too much, you can add material back on and try again.   But still, it can be a long, slow, process.  And there are times when it can be hard to imagine that the piece will EVER look like what I want.  It’s kind of like the carving of Mount Rushmore.  When they first started blasting the mountain, I’m sure the designer looked at the jagged standing rocks and the heap of rubble and wondered if it would ever pull together.  But bit by bit, it did.  

 

Finished sculpture for the corgi head door knocker

Finally, the finished corgi head. sculpture which will become a door knocker

When I get stuck, I’m glad to have my own living models close at hand. My dogs, cats, and horses are philosophical about being pressed into service so show me a pose, or exactly how a nose is constructed or how hair blows back on the run.  It usually takes several weeks of carving and tweaking (and walking away and coming back with fresh eyes) to perfect a design.

 

 

The studio mold

The studio mold lets me cast a wax to work on, as well as a cold cast model for display.

The studio mold lets me cast a wax to work on, as well as a cold cast model for display.

 

 

When the sculpture is finished, I make a temporary mold in my studio and make a cold-cast model, both to see the influence of color on the piece, and to have something to show to potential buyers.  If it still looks good, I use the same mold to cast a wax, this time in a wax that takes and holds detail to perfection.  Using the cold-cast piece for reference, I carve and refine any details that need touching up.  It’s this wax that goes to the caster.

Mold making and wax casting at the foundry

The permanent mold is used to cast wax replicas of the original.

The permanent mold is used to cast wax replicas of the original.

 

 

Irish water spaniel waxes treed for casting

Irish water spaniel waxes treed for casting

Using my wax, the caster makes a professional-quality mold, which will allow him to make perfect copies of the original.   Each wax new wax is checked carefully for defects, and then joined back-to-back to another wax to make what’s called a “tree”.  I use a small artisanal caster right here in Vermont, so he usually casts in batches of eight (four pairs in trees).

 

 

Preparing for casting

Caster inspecting a row of door knockers dipped in ceramic slip and sand to create the shell for casting.

Caster inspecting a row of door knockers dipped in ceramic slip and sand to create the shell for casting.

Each pair of waxes is dipped in layers of ceramic slip and sand to form a shell. It takes a week or more to build up the layers, allowing the shell to dry each time. Then the finished shell is fired in a kiln, causing the wax to burn away from the inside.

 

Casting the metal

While the ceramic shell is being heated, the artisan melts the metal  For one or two pieces, the metal can be heated with a torch in a graphite crucible right on the top of the work bench.  For bigger batches metal is melted in a forge or kiln.

Gold melts at 1948 degrees fahrenheit, silver at 1763 degrees, and bronze at 1748 degrees. When the metal is hot enough to flow, the caster pours it through the cup-shaped opening into the still-hot shell.

Lost wax casting can be very high tech.  Modern vacuum equipment can run tens of thousands of dollars.  So can a commercial-sized burnout kiln or melting crucible.  But small artisanal casters can still achieve excellent results with homemade equipment, skill, and experience.

 

Finish work

Applying the patina to a freshly cast bronze dog doorknocker

Applying the patina to a freshly cast bronze dog doorknocker

After the raw castings have cooled, the ceramic shell is chipped away and the sprues (the channels that the metal followed through the plaster) are cut and ground away.  If the sculpture has been cast in more than one piece, the parts have to be welded together, and every seam ground and redetailed.

Then the piece is polished and finished with a patina to enhance the detail and preserve the color of the metal through the years.   Seeing a carving transformed into a finished piece in metal is the closest thing I know to magic!