Help, please: Melting precious metals, HOW

Ed Westerly · May 21, 2012

I have become interested in melting precious metals (mostly gold, to start) and have tried with a burnzmatic torch, with little success.

I asked Ron Smith, and he told me to get a "jeweler's torch", which I thought at the time was enough info. :biggrin: Since then I have gone to google and found about half a million torches, each calling themselves a jeweler's torch, but verying hugely as to size, heat output and cost.

Please tell me what you use and be specific as to model number and if you could give me some idea of cost, that would help too. :thumbsup:

Thanks in advance. :clapping: :tiphat:

Sandy · May 21, 2012

Hi Bruce,
I use the Smithy Little Torch, http://littletorch.com/kits.html I have not used it on gold but it does great on silver. I also use propane for the gas. Good luck :tiphat:

Sandy

GTJC460 · May 21, 2012

Are you looking for something to be able to cast an ingot or other casting? If so I would recommend getting a prestolyte atmospheric acetelyne torch. Basically with this torch you cant overheat and damage the metal. Yes it will take longer to melt the gold or silver, but the plus side for inexperience will far outweigh a costly mistake. You can pickup a kit at your local welders supply store that includes various tips, the regulator and hose. All you need then is a "B" sized acetlyne tank or a large tank and "B to regular" fitting. I think you can get this package without the tank for around $100-150.

Use a #5 or #6 tip to melt the metal

This is what I use for casting all gold alloys and silver. It's what was typically used by plumbers to solder pipes.

For platinum you will need either and oxy/propane, or oxy/hydrogen torch and alot more other stuff.

If you are looking to do simple light work like ring sizings, soldering, and repair type work, you cant go wrong with a hoke torch to match the fuel type you want to use. If you have natural gas at your studio, get a plumber to run a line to your bench. This is what I use for all light soldering, annealing, and melting work at the bench.

I'm not a big fan of the little torch system, as its just too small in the hand. But for the 20 years I've been a jeweler, I have always used a hoke torch for bench work, and the prestolyte for casting lower temp metals

Ed Westerly · May 21, 2012

Thanks for the answers (and so quick, too!), Sandy and Bert. Bert, a couple of additional questions. What is a "hoke" torch, and are you talking the big acetelyne tanks, or the small ones? Also what's the difference between "prestolyte atmospheric" and just plain acetelyne?

Thanks

James Roettger · May 21, 2012

I prefer a regular welding torch. I use a Smith number A 10 welding head with propane and oxygen fuel mixture. You will never be able to melt platinum with a prestolite acetylene air torch. Melting 24K is somewhat difficult without oxygen. An acetylene air torch albeit simple to use is really best suited for just hard soldering and makes a barely adequate torch for alloying (melting pure with alloy ingredients) gold. An oxygen mixture will be a better investment as you can buy a mini torch for soldering and a full size welding torch for the melting. Also, If you get into any kind of larger melts you will need the versatility of oxygen.

Scratchmo · May 21, 2012

For casting ingots you may want to check out the Kerr furnaces. They are small, hand-held furnaces that use graphite crucibles. Once they reach proper temperature, they are as easy as pouring a cup of coffee. Unlike torches, there is no risk of blowing out precious metals from the pressure. One drawback is that they only go up to 2050 degrees F. Not good for platinum.

Chujybear · May 21, 2012

I like oxy propane. I can't help you with brand. I've used lots of torches, an never known the brand, but they all melt gold fine. It's nice to have a few heads you can attach to it.
I have a little torch at my bench, which is okay. I can weld gold with it, but I had to make my own head for it.

Joe Jacob · May 21, 2012

Ed
As you can see from the replies there are many types of torches in use depending on your needs and preferences. Check out some jewelry supply sites, like the one listed below. They have many types of torches. I have both the Hoke Jeweler's Torch and the Smith Little Torch as well as a full welding torch set up. I use what is required for the size of the job at hand.

http://www.contenti.com/products/soldering/torches.html

metairieclark · May 21, 2012

most people i have known usually stay away from acetylyne , propane or natural gas with oxygen , and a hoke will melt up to about 6-maybe ten ounces of gold any karat , if you want to melt platinum for whatever purpose you are probably looking at a few bucks , and a much bigger torch , probably the electric furnace/melter would be better , remember to heat the ingot before you pour hot metal into it , don t want to see it blow up in your face ,been there done that , got a piece of molten gold buried in my chest , had to dig it out , and lucky it didn t go into my eye, thank god

GTJC460 · May 21, 2012

This is hoke torch I mentioned: http://www.gesswein.com/p-7667-hoke-jewel-torch.aspx

I like it as the knobs are just right. I personally don't like the ones on the little torch.

The atmospheric torch uses the air in the atmosphere to create a nice reducing flame. It really depends on what you plan to do. For instance, I just recently had to cast a very heavy 10k white gold item. It required 3.5 Troy ounces of metal. This was about the limit of acetylene torch. The metal involved has a melt and flow temp for casting around 1950' in the alloy I was using. With this large of a metal volume it was very difficult to get the metal to the right fluid state.

However, smaller volumes of 10k white have never posed a problem. 24k melts pretty close to that which was required by the 10k white. So that said, if you plan to melt 2+ ounces of 24k, then I would definitely suggest a torch setup that burns hotter. If you plan to do small melts <2 ounces of high karat gold the acetylene prestolite will work just fine.

BTW, I also use a hydrogen/oxy torch for my platinum castings. Working with this setup is a totally different experience and it's really easy to get your gold alloying metals too hot and burn them up. Just food for thought I know if I was inexperienced at melting metals, I know which setup I'd choose.

Lastly the prestolite doesn't need a huge tank. The B size tank looks like the size of two 2 liter bottles of soda put together. It's the smallest sized tank you can get for acetylene.

Whereas if you get into propane or other gases you will be buying much larger tanks, as that's just the way those gases are sold. Propane has it's own issues. Oxy/acetylene burns really dirty. Hydrogen is very hard to see the flame.

GTJC460 · May 21, 2012

This is hoke torch I mentioned: http://www.gesswein.com/p-7667-hoke-jewel-torch.aspx

I like it as the knobs are just right. I personally don't like the ones on the little torch.

The atmospheric torch uses the air in the atmosphere to create a nice reducing flame. It really depends on what you plan to do. For instance, I just recently had to cast a very heavy 10k white gold item. It required 3.5 Troy ounces of metal. This was about the limit of acetylene torch. The metal involved has a melt and flow temp for casting around 1950' in the alloy I was using. With this large of a metal volume it was very difficult to get the metal to the right fluid state.

However, smaller volumes of 10k white have never posed a problem. 24k melts pretty close to that which was required by the 10k white. So that said, if you plan to melt 2+ ounces of 24k, then I would definitely suggest a torch setup that burns hotter. If you plan to do small melts <2 ounces of high karat gold the acetylene prestolite will work just fine.

BTW, I also use a hydrogen/oxy torch for my platinum castings. Working with this setup is a totally different experience and it's really easy to get your gold alloying metals too hot and burn them up. Just food for thought I know if I was inexperienced at melting metals, I know which setup I'd choose.

Lastly the prestolite doesn't need a huge tank. The B size tank looks like the size of two 2 liter bottles of soda put together. It's the smallest sized tank you can get for acetylene.

Whereas if you get into propane or other gases you will be buying much larger tanks, as that's just the way those gases are sold. Propane has it's own issues. Oxy/acetylene burns really dirty. Hydrogen is very hard to see the flame.

GTJC460 · May 21, 2012

As another note, custom jewelry is all I do. I'm casting every week 3-4 times per week in sterling and karat gold. The prestolite is what I'm using on all these jobs. I only use my hydrogen setup on platinum. The range of product varies from 10 oz trees of sterling pieces to 1 dwt items in 18k. You can do alot with this setup.

Last thought. The nice thing about torch melting for ingot pours is that you can put your crucible right up next to the ingot mold. Doing this allows you to kill two birds with one stone. You heat the metal and the ingot mold simultaneously. With an electric melt furnace you have to do this separately.

What happens if you don't heat the mold? The metal can explode up and out of the mold when you pour. I've never had it happen with a torch melted pour. Get a burno style crucible. I put mine in a cast iron skillet. Then put the back of the crucible ad close as possible to the mold, thereby heating both together.

James Roettger · May 21, 2012

The reason metal can explode out of a cold ingot mold is because water vapor forms on the mold as you bring the flame and crucible up for the pour. Water vapor is a by product of the flame and the room temperature mold is at the "dew point" of the hot flame. At the beginning of the melt the mold should be heated to well beyond the point when water vapor was last seen forming on it. This is approximately 300 to 400 degrees fahrenheit. Then as mentioned, melt the metal adjacent to the ingot mold and let some of the flame cast itself for several seconds onto the ingot mold as you approach for the pour. If the metal lands on condensed water vapor boiling and explosion occur. so really the mold only needs to be beyond the boiling point of water and not super heated or red hot. If the molt is too hot the gold will melt right onto the mold and be wasted. Eye protection in the form of at least #5 welding glasses should be worn as well for two reasons, to protect from flying metal obviously but more importantly, to keep from burning your retinas. The infrared heat is what can damage your eyes, even though it is not uncomfortable to look at a pool of molten metal, the infra red can slowly damage your eyes over time from repeated exposure.

Ed Westerly · May 21, 2012

Well, thanks guys.
I now have several very good areas to look at.
I like the electric furnace idea, as I've been wanting one for heat treating gun steel, color case hardening, etc. ,so I may go that way, but at least now I have a good idea of what torches will work if I need to do it that way.

Thanks again. You've saved a life!

James Roettger · May 21, 2012

I can't say I know anybody in a huge world of jeweler friends who use furnaces to melt. Takes a long time as you are heating the entire crucible through and through to melting temp, oxidizing atmosphere would wreak havoc on small quantities of precious metal. That's more like bronze casting or something huge. I would definitely want a "show me moment" from someone before I used a furnace to melt a half ounce of metal. Sounds like what you need is a torch for melting and a kiln for heat treating gun steel. At this point what you could do if you want to melt some 24K to make inlay wire is take a charcoal block from a jewelers supply, cut a 1/8" wide and deep and 1/2" long groove into it. Take your Bernzomatic propane/air torch and try melting the metal with that. Lay the metal on the charcoal block and as it melts it will fall into the groove forming an ingot. The charcoal will gather and amplify the heat allowing you much greater capacity than could be obtained with a crucible.

Barry Lee Hands · May 22, 2012

James, I agree with your recommendation. I use a bernzomatic propane torch from the hardware store and an asbestos block I have had since I was about ten years old. I can mix and melt many kinds of karat gold on it up to about one half of an oz , of course charcoal is safer, hehe.
I can even melt pure platinum on it if I have a full propane bottle.
At one time I had a tiny induction furnace with a ceramic crucible which worked great for small melts, until it burnt out.
When I was doing casting as a kid( my mother was a jewelry instructer) she had lots of cool stuff I could use , including an oxy propane bench torch that would easily melt a couple of Oz's for centrifugal lost wax casting.

Mike Cirelli · May 22, 2012

I would get a prestolite torch as Bert suggested. They are very efficient for melting gold and silver. They prestolite turbo gets very hot and can melt 3 or 4 oz rapidly. I wouldn't use a hoke unless you are going to be doing very small amounts (1/2 ounce or less). If you are making wire here's a how to http://igraver.com/makingwire/

Doc Mark · May 22, 2012

Mike, great tutorial! I just bought a crucible. Can I treat it with Borax alone (All I have on hand right now) or must I add the Boric acid too? Does this coating need to be renewed after a few uses? Also, if you pour off all of your molten gold, then why must this crucible only be used for the same carat gold from then on? Thanks again for your sharing.

Ed Westerly · May 22, 2012

Ask and you shall receive! Great info. keep it coming, I am learning alot!

GTJC460 · May 22, 2012

The idea of using separate crucibles is to prevent contaminating your different metals. For pouring ingots it's really no big deal, but when casting it becomes more of an issue.

I've got one crucible each for white gold, yellow gold, silver and platinum. Rose gold gets cast in the yellow crucible. Trace amounts of metal get left behind in the borax so that's why most people recommend using dedicated crucibles.

I forgot about the charcoal block method. I use this too when it's easier/more convienent on small melts. The smaller soldering torches like the hoke work adequately for this method.

For ease of use and cost the prestolite is hard to beat.

Help, please: Melting precious metals, HOW

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