Making a Sand Cast Bronze Sculpture

Here's a sculpture that I made a few years ago that combined cast and fabricated bronze. Bronze casting can be done in your back yard if you have a leaf blower and a small refractory furnace. Sand casting, in particular, is a fast and cheap way to cast metal.

Step 1: Start Making the Mold

Adding sand to the flask.  The flask can be made of metal or wood, must register well and be able to withstand the pressure of compacting the sand. 

Step 2: Pressing the Pattern Into the Sand

This pattern is made of wax, but patterns are often made of wood. The pattern will later be removed from the mold and bronze will be poured in the cavity created from the pattern. 

Step 3: Ramming the Sand

The sand needs to be compacted to hold its shape when the pattern is removed. Use a tool to hand pack the sand around the form until it is super dense. 

Step 4: Making the 2nd Half of the Mold

After the bottom of the flask has been rammed, talc is dusted over the surface of the pattern and sand to act as a release agent. 

Step 5: Adding Sand to the Flask

Put the flask together, sift sand over the pattern and evenly continue to add sand until the flask is full. 

Step 6: Ramming the Sand

Ram the hell out of it. Continue adding sand until it completely fills the flask. 

Step 7: Screed the Mold

Run a straight edge along the top edge of the flask to remove any excess sand. 

Step 8: Separate the Mold

Separate the mold and remove the pattern. If you did a good job, you'll get good detail and shape accuracy. If it falls apart, feh!

Step 9: Adding "Gates"

Channels, or "gates", need to be carved into the sand to give the bronze a way enter and fill the mold. 

Step 10: The Finished Mold

After the gates are cut into the sand, put the flask back together and you're ready to pour. 

Step 11: Make the Metal Hot

Heat the bronze to about 2,150 degrees Fahrenheit. Safety first!

Step 12: Pouring the Mold

Slowly fill the mold--this is the fun part. 

Step 13: Clean Your Casting

When cool, your bronze will easily separate from the sand but you'll need to clean it up a bit and maybe fix some imperfections in the casting. Sand blasting and wire brushing works great for making it pretty. Now you're ready to patina, or use the casting in a larger piece. 

Step 14: Fabricating

Beginning to fabricate the geometry around the casting for a wall hanging sculpture. Start by tack welding the forms together. 

Step 15: More Fabricating

Keep tack welding until the entire piece is together. Then weld the whole mess up, dress the welds (if you want) and make it nice. 

Step 16: Applying a Hot Patina

Clean the metal and then apply heat and chemicals: in this case ferric nitrate, cuprice nitrate and ammonium sulfide. This part is a little bit voodoo. 

Step 17: Finished Piece

Wax the sculpture with a couple coats of carnuba based wax and, presto, you have a bronze sculpture. Good luck!

Comments

[karlosf1]

There's a crack in it 🤣.

[frogisamoose]

I have a small sculpture that I made in oil based clay. Based on what I see here in your demo. it would be quite difficult to cast several copies in bronze. That being said, can you refer me to a studio where I can have someone make bronze copies of this piece? is a of a man sitting in a chair and measures roughly 6.75 inches high by 2.50 inches wide. There would be several undercuts.

[mp7042867]

Hi. If you have a sculpture you want to replicate I suggest lost wax casting. Use silicon rubber to take a mould of your part. Cut the silicon to remove the original and then pour in wax. I have made a few simple parts and given the wax replicas to a specialist foundry. My parts were medical instruments cast in stainless steel but the principal is the same

[PeterC104]

What kind of sand works best?

Also, it is a butt made of bronze

[PeterC104]

He is making a bronze butt. Did anyone else notice?

[skaue]

Be prepared for a quite a bit of work when it comes to clean-up after casting. There usually is a little bit of flow out from the seams of the two halves of the sand flask/casting mold - near impossible to get a perfect seal. This might not be a real issue, but a tight seal and good leveling of the contacting surfaces go a long way. If working with very hard metals like nickel and bronze, don't do sloppy work here. One important thing to remember when making your model/plug: Its shapes MUST be able to release between two mating layers.

If you don't want to go about carving in the sand after packing it, I highly suggest putting in a few conical wooden dowels before packing the sand. Minimum of one for pouring, another for venting - more for larger surfaces. Make sure the dowels touch your model when packing the sand.

There are also a large variety of specialty sands, materials and binder materials available, to make the sand molds less fragile. If using these, remember that the sand molds actually need to come apart afterwards.

(Former foundry worker, molding and sand-casting marine prototypes and ornamental figures)

[masterbeatty]

Maybe it's just me... But the finished product looks the the backside of a woman...
Either way, neatest thing I've read all week!

[alltidandreas]

Nice pictures!
Why are you adding chemicals in the "voodoo" part?

"in this case ferric nitrate, cuprice nitrate and ammonium sulfid" ?

[albertdicruttalo]

I say voodoo because the patina can be unpredictable. There are many variables and as a result, your desired patina can be difficult to achieve.

[dchall8]

So the bronze flows between the two layers of sand even though they were packed tightly together? Can you control how thick the bronze is?

[astral_mage]

theres a web sites dedicated to metal casting.

[albertdicruttalo]

The bronze doesn't flow between the layers of sand. When packed, the sand creates a tight enough seal to prevent that from happening. Instead, the bronze flows through the gates carved into the sand to fill the mold. The thickness of the pattern, ideally about a 1/4" depending on the complexity of the form, determines the thickness of the casting. Hope that answers your question.