Bronze Bowl

by Ben N on January 22, 2024

About a month ago, I got a propane forge. It’s designed primarily for blacksmithing, but once I realized that it could get hotter than the melting point of brass and bronze, I had to give METAL CASTING a try!

A few little casts gave me some great experiences fast! I especially like how the Trilobites turned out!

I’ve made numerous small parts so far, including a trigger guard for a flintlock pistol, a bottle opener, and a bronze spoon!

Since I was building up my skills, I figured that a BOWL might be the next most complicated thing.

My wife has several small orange bowls which she inherited from her mother. They are a great retro orange color. Unfortunately, they are just plain ceramic, and they DO break.

I thought I’d try using one of them as a pattern for a bronze casting. The bowl is a neat shape and even though I can only cast a pretty small amount of metal right now, I SHOULD be able to heat just large enough of a volume to make one.

I’m creating sand-casts. These are simply molds in which a person packs sand around an object to leave an impression in it. The mold is split open, The original pattern removed, the mold is closed up again, and molten metal is poured in the empty space.

For the metal, I’m using 95% salvaged/recycled Copper and 5% elemental Silicon. This is a “Silicon Bronze” and is pretty close to an alloy which bronze sculptors like to use.

I created the sand-mold, melted the bronze, and poured it into the sand-mold. Unfortunately, I didn’t estimate the volume correctly. There just simply wasn’t enough metal to fill it up.

Back to the drawing board….
I made a new sand mold, cut up my failed casting and melted it AND some additional material in the forge. Then I tried casting #2.

This time, the mold filled all the way up, BUT… after examining it I saw that it really wasn’t a great casting. There were numerous odd-shaped voids visible on both the inside and the outside of the bowl. So, this bowl wouldn’t be great for actually eating food out of, but it could still make a great art piece.

I have a 2″ sanding disc that I can put in my cordless drill. I used that and increased the grit of sand-paper starting at 40 grit and working my way up to 2000. I was able able to mount the bowl in my wood lathe. By spinning the bowl AND sanding it with my cordless drill, I was able to get the interior pretty smooth!
I finished it by shining with some Mother’s Chrome Polish.

I wanted to leave the exterior of the bowl rough. I also really like the type of patina created by applying Liver of Sulfur. That’s an oxidizer which will darken brass and bronze. I heated the bowl with a propane torch and then daubbed on the L.O.S. with a shop rag. The bowl turned a dark gray.

In a weird accidental discovery, I realized that I had given the interior of the bowl an amazing rainbow finish! Bronze will change colors depending on how it is heated. By chance, I got this incredible finish. Unfortunately, it was only surface deep, and I found I couldn’t keep the rainbow. I re-polished the inside back to a golden shine.
I’ll have to do some further experiments to be able to take advantage of these tempering colors in the future!

On the exterior of the bowl, I polished it down with #0000 extra-fine steel wool. This removes the oxidation from the higher parts of the surface, creating a bright highlight against the darker low areas. It provides a nice contrast on the rough sand-cast exterior.

Overall, I’m very happy with the bowl!
It even sounds good!
Any why not? Bronze is the traditional metal of bells!

The one big limitation that I have right now is how MUCH metal I can cast. The propane forge is NOT designed to hold crucibles. So, I can only fit a very small one inside.

I hope to soon get a melting furnace! The PROPER piece of equipment for metal will allow me to be able to melt much more at once. This opens the door for larger pieces or to be able to make multiple castings at once!

Needless to day, I’ve been watching a lot of metal casting videos on YouTube lately.
My favorite metal-casting YouTube channels are:

The Lundgren Bronze Studio videos are especially good, as the host not only shows all the steps, but also his mistakes and everything else in the learning process. Good stuff.

Well, I’ve been having a lot of fun casting metal. Being able to take scrap materials and completely transform them into something else is absolute ALCHEMY!
While I’m not turning lead into gold, scrap copper, tin, and silicon into art is a pretty close second!

Until next time, stay charged up!
-Ben Nelson

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