Todays question is actually several … I purchased some casting bronze a while back as I had an upcoming task to creating some large (1 inch across x 2mm thick) pins …weigh around 5.5 grams
I have mainly worked in gold for decades and have worked out the bugs in those lost wax castings but still have the odd issue… but bronze is a new thing
1… Anyone have a suggestion as to a type of high quality jewellery grade bronze to use … and a source?
2 … I did my first bronze casting yesterday using the material I have been storing… bought it ages ago and do not know the alloy I was surprised at how long it took to melt (acetylene torch with a little borax)
The castings are a mixed bag … some are ok and will be usable others look rough like I overheated the metal or cast with the flask temp too hot (I dropped it to around 750F) before casting
3 , Any other resources to help guide me to making nicer castings would be a pleasure
Thank you in advance for all previous input on other topics
All the very best from way up here in the frozen North
Way back when, I got a Masters in Sculpture degree and did a lot of bronze casting. I learned that my favorite bronze alloy is Everdur. It’s a slightly different silicone bronze alloy than the one you are using, which known as Herculoy. The biggest difference is that Everdur doesn’t have zinc. I’ve grown to hate melting any alloy like Herculoy with that much zinc. Everdur melts cleanly, casts with good detail and doesn’t give off clouds of zinc fumes.
Now that I’m only making jewelry scale objects, I get my Everdur silicone bronze from Altas Metals in Denver. What I love about Atlas Metals is that you can buy silicone bronze in 1/2" cubes in fairly small quantities. Although I must admit that I usually buy about 25 pounds every 10 years or so.
Again, these days I only cast lost wax, jewelry scale objects and Everdur bronze works great.
It was late last nite when I cast the bronze and I didn’t really notice the zinc but I could feel it today… Not good stuff to breathe for 10 minutes
I will certainly give Atlas a look and place an order Really appreciate your taking the time to let me know!
Question … Is there any particular flux to use with your Bronze? The 2 pieces I discarded from yesterdays casting both had borax inclusions that I couldn’t think of trying to repair… I thought I was very thrifty on the borax during the melt…
i am not sure what difference it might make, if any…but perhaps your alloy is brass…?…i always thought bronze was copper and tin…and brass was copper and zinc…?
i recall this also because i was trying to figure out if i could TIG arc weld either…i was talking to orion tech support, and he pointed out that the boiling point has an impact…ie: the brass and bronze both have low melting temps, but the tin boiling point is higher than the copper melting point, so it shouldn’t vaporize during welding…whereas the zinc boiling point is below the melting point of copper, and it will vaporize before the copper melts/ welds…(i am paraphrasing here, please forgive)
I use to work for a large foundry here in New Mexico and they used Everdur only and Tig welded it with little trouble. I have a small casting setup and also only use Everdur from Atlas Metals been very happy with the resultz.
Also Atlas also has the Everdur Tig rod.
I’m guessing that you’re doing centrifugal casting? Is that correct?
You’ve got to be careful about using too much flux. There’s a bunch of different ways to add flux, but sometimes with centrifugal casting, I’ll pre-melt flux into my crucible. Whatever you do, you don’t want to blow powdered flux into your flask with your torch. These days I’m doing vacuum casting in a fancy nitrogen atmosphere casting machine. The J-2R from Rio Grande. That set up can melt about a coffee cup of metal and doesn’t use flux because the metal melts in a nitrogen atmosphere. But I did centrifugal casting for decades and I’d use whatever flux was around. I suppose Matt’s Casting Flux from Rio Grande is my favorite if I have to pick one.
The other issue with bronze is that there is slag. It is best if you can scrap the slag out before you cast with a carbon rod or something.
With larger sculpture bronze casting in a foundry (say 50-200 pounds), we’d scrape out slag as needed with a heavy steel spoon kind of a thing, wait for the molten bronze to swirl on top, then toss in a packet of about 1/4-1/2 cup of borax wrapped a paper towel right before pouring. The way we’d tell if the metal was the right melting temperature was to dip a steel bar into the molten bronze. If the bronze stuck to the steel bar, the molten metal was too cold. If it was the right heat then it’d fall off and not stick. I’m sure that you could do a similar thing with a steel coat hanger or something with centrifugal casting crucible. Remember that casting temperature is about 100-150 degrees hotter than melting temperature for most jewelry metals.
Rio Grande does sell a very pure bronze alloy called Ancient Bronze that’s fun to cast with. It’s 90% copper & 10% tin. An advantage of that is that it comes in little balls like regular casting grain.
I gave a demonstration once to an Archeology class at the college that I teach at, where I alloyed some 90/10 bronze myself and then forged it out into a butter knife. I was surprised how easy it was to do. I bought the pure tin from McMaster Carr and used copper electrical wire. (someone told me that’s the purest copper that easily available).
Finally for a long time, I cast production pieces in Shibuichi, which is a Japanese copper and silver alloy that I mixed myself. It’s basically a bronze alloy, except that you replace the tin with silver. 80% copper, 20% silver is a common formula, but you can divide it up however you want. 70/30, 90/10. Pure copper is a hard metal to cast with, but adding in a bit of silver makes it flow really well.
I think that’s all I know! Have fun and let us know how it goes!
I also use everdur (silicon bronze) exclusively for bronze work. I melt it in a clay graphite crucible in a kiln and pour at 1160⁰ C. I get my alloy from Sipi Metals but they only sell 20lb ingots. However it’s the best quality silicon bronze I’ve come across. Atlas is really convenient though that it comes in useable chunks.
Keep in mind that bronze finishes best with a colored patina, if you intend for a deep gold color you’ll be fighting oxidation for eternity.
Any bronze that has zinc in it is technically a brass. Brass holds a gold color but I avoid it like the plague because of how messy it is.
I like to use #392 Bronze shot from United Precious Metal Refining, Inc. (www.unitedpmr.com). It’s great for making models, line samples (instead of actual live gold samples for security and economic purposes), and bronze jewelry. It polishes up like 14KY. You can also pour ingots to make sheet and wire. I cast with a centrifuge and it casts beautifully. I solder with gold solder, though if you’re just making models and need to solder on parts or sprues and don’t care about color match, you can just use silver solder.
When I worked for a large jewelry company, we also vacuum casted models with the same Neutec vacuum casting machine used for gold production casting. You can cast production wax trees in bronze, using the same large perforated flasks.
Of note, UPMR requires you to have a commercial license and will not sell to nonprofessionals. They sell other bronzes along with the usual precious metals.
It sounds like you’ve gotten some good suggestions about sources of bronze, so I won’t get into that. I’ve mostly used the Herculoy silicon bronze alloy, which I like because it melts so cleanly. It doesn’t really need flux to melt, but I use it anyway to help skim off the dross that floats on the surface of the melt. Silicon bronze casts well in a centrifugal machine, which it sounds like you’re doing. It’s good to keep the flame on the melt right up to the end; tiny amounts of metal like that tend to freeze up quickly. This also gives you an opportunity to skim off any little bits of flux floating on the surface before they’re flung into the mold cavity.
In my experience, rough-looking castings with poor surface quality are usually the result of metal shrinkage. If there’s not enough liquid metal available from the sprue as the piece cools, it will draw metal from the surface, causing porosity and that typical rough appearance. Try a fatter sprue next time, into the thickest part of your piece, or incorporate a sacrificial shrinkage reservoir if the sprue alone isn’t sufficient to provide the feed metal required.
We use Herculoy to cast belt buckles centrifugal with a torch. Have found the flux that works best for us with Herculoy is Johnson Matthey Easy flow flux powder. Could not find it from US supplier. Ordered from England on Ebay.
Thank you … Love to see your nitrogen casting setup at work! Great information!!!
Thank you so much! (I was taught decades ago to add a tiny bit of flux to the melted metal just before casting and interestingly I always have some flux pitting on some of my castings which generally ruins them!
Will order some of that Matt’s casting flux today!
Here’s info about the J-2R vacuum casting machine. It’s pretty great! Like I said it can melt about a coffee cups worth of metal in a nitrogen atmosphere, so there’s no need for flux. While it’s designed for small scale production jewelry casting, it’s especially advantageous in a school setting as there’s almost no chance of molten metal spillage. That said, it is an expensive casting solution. Traditional centrifugal and vacuum casting set ups work best for most folks.