Let's Talk Smelting--Heat Source Equipment, Furnaces? Torches? Backyard Foundry? Options

[Si_NM]

GT,, in years gone by, I used to do assaying,, the electric furnaces are awful,, but the old Denver fire clay muffle furnaces are correspondingly good. They use blown air and a spray of diesel fuel to heat with. Everything is a variation of the same theme on lighting the things. As with melters, first you get a gentle air flow going,, then have ready a flame source,,, this is the tricky part as the stand alone flame can get blown out in just flowing air. As one gets experience tho, this is still the preferred way to light. After you have an air flow,, and the flame included,, then apply the fuel whether it be propane, diesel or whatever. This way you dont overfuel before applying flame. The trick is to get a flame source that is tenacious and not prone to easily being blown out as like a match. My oil soaked canvas just burns hotter in the air flow til the fuel is applied. You need to be on top of things,, it's a quick succession,, air , flame, fuel,, you cant eat a sandwich in midst of process,, hehe. Hope this splains things..

[gold_tutor]

Si's talking scorification (a smelting technique) in the For Sale--Scorifier Dishes section of this forum.

I put up some illustrative digital pix ystdy...might want to check out the new info, gals/guys.

[prospecta04342]

Hi Si, don't ya just love the surface color of molten gold!! I've always been impressed with that! I used to run an art foundry and still have a small furnace out back. Had a lot of fun , mostly greensand castings, and lots of bronze. Thanks,, John

[prospector_41]

You must use a very long long match to light it. :D

[EMac]

Are there any folks that do smelting on here still? Seems there were some folks in the past, but I'm not sure if they're still active. This is something I'd like to learn how to do.

[Denise]

Correct EMac, Megan(gold tutor) and Bill(Si NM) are no longer active on the forums but there is some great info in this thread.

[swizz]

Emac... I found this while shopping for V-mat: Microwave Gold Smelting Kiln
Not exactly cheap but looks fairly straight forward.

[Laughing_Guest]

This may be an older thread, but I figured that I would post some of my information on backyard casting.
First let me outline the process as I see it. There are four things totally necessary for the melting and pouring of red metals: a fuel for burning (wood, coal, diffused gasoline/diesel...), air, a way to keep the heat, and something with a higher melting point than what you are trying to melt (crucible).
Let's talk about air because any fuel for fire will work. Air is what will boost the temperature of the burning fuel and so is the most important aspect. Your air source can be a fan, a hair dryer, a hand crank blower, or even a bellows if you have the energy.
Now that we have established that we need a fire with added air for heat let's look at the humble Dakota Fire Pit. It is a hole the size of the intended fire dug straight in the ground with another hole a few feet away dug at an angle to connect to the bottom of the first hole. The first hole is the fire pit and the second hole you connect an air source blowing into the fire.
The next important element of this rig is the backyard crucible. I have used a steel coffee can with four foot steel rod poked through both ends of the top to dangle it into the hole, but anything with a melting point higher than what you are trying to melt and the ability to hold the liquid metal without exploding will do. To pour the metal from my coffee can rig I use another metal rod that I have rounded around the anvil horn to fit loosely around the bottom of the can.
I will spare you the details of the actual heat and pour as I figure it should be fairly self explanatory, but I will say some things about molds. Molds are relatively unimportant unless that is your thing, but it can be as simple as a dugout in the ground (although that tends to produce bubbles from the water in the ground boiling on contact with the molten metal) or a hole drilled into a piece of hardwood (an old shotgun slug casting technique I had learned which produces great results for the simplicity).
That should be enough to get the ol noggin kickin around a little on backyard smelting. I figured that this info could be helpful, but don't don't go tryin' anything cuz I said it. It is ultimately a fairly dangerous endeavor and should only be undertaken at your own risk and with utmost caution and care. Have a good one.

[EMac]

The furnace to use is definitely a concern; I was looking at the microwave sets, and there are also furnaces/kilns available in the $300-500 range. Initially, I hope my friend's glass kiln can reach 1100C and they'd let me use it. Digging holes in my backyard to make a furnace isn't in the cards. I'm also the guy who got C's in wood shop; building things well by hand ain't my strong suit. Things I build generally work, but aren't pretty, and may break...I leave things like this to people like Swizz with those talents.

The basics I can read about...I'm interested in going to watch someone do the process without damaging themselves or surrounding areas. Things like proper PPE, ventilation, handling/pouring of molten metal, what flux to use and how much of each, etc. Ideally I'd like to find someone that does this regularly to learn from.

A few articles to whet appetites:
American International Journal of Research in Science, Technology, Engineering & Mathematics
ICMJ Extracting & Smelting Your Gold (Subscription Req'd)
ICMJ How to Melt Your Own Gold (Subscription Req'd)
ICMJ From Curiosity to Mine Owner - Pt II (Subscription Req'd)

CM Hoke's book in pdf:
 refining_precioius_metals_waste_cm_hoke.pdf ( 2.04MB ) Number of downloads: 5965

[Caveman]

A couple of old timer type guys out here use retired blacksmith's (ferrier's) forges (foundries). Not large, hot enough to melt iron, ad were cheap.... they run on propane.

[Bryan K]

I have also been looking at smelting techniques. If a guy was to pan his cons down to black sand and use a Chapmans flux furnace that looks like it might just do the job. But then you have the added cost of using the substrates to get the job done. I'm not a fan of the Blue bowl. I can classify and use A tap method with my pan to pull the gold out faster than a blue bowl. It would be nice at the end of the year to be able to just smelt the fruits of my labor.

[EMac]

I plan to collect more gold before embarking down this endeavor. I definitely want to learn smelting, and also refining; I did a bit of reading on the chemistry (mainly inquarting), and it looks doable with the appropriate safety precautions. If someone else plans to try smelting/refining or already does it, and you're willing to let me observe and ask questions, I would be immensely grateful!

[gold_tutor]

Hi, EMac, I'm not in a position to hold in person instructional set. However, I can still answer questions.

The small, Microwave furnace technique taught by Dr. John Milewski is a gooder. Bought my cheap microwave at a local department store...Fred Meyers. Set me back a $50 bill. And then the fire brick are extra, so are the tongs, gloves, crucibles, mold's etc.

There are also pretty cute small round furnaces powered by one or two MAPP gas torches, which hold potential for you to consider. The drawback on these is that you can only use a small, dense, carbide crucible in this unit. That's a limitation I don't like. Some smelts require the smelt to "borrow" silica from the commercially manufactured fire-clay crucibles. The metallic carbide ones don't have any silica in them, so there's nothing to borrow, and that contributes to smelt failures right and left.

And I still think the brick and angle Iron model I posted, or at least think I posted up above, work really really well. They and the Microwave furnace will both use standard clay crucibles. And for the record, I prefer to buy my clay crucibles from the good folks in Sandy OR, aka Action Mining. She and Mike go through hundreds of these per year themselves, and have learned which ones are the best buy, and ship them in in quantity. Nancy prefers Australian Sheepbone sourced crucibles, and I just don't buy mine anywhere else. I can get an average of 3 separate smelts per crucible because my fluxes are balanced and don't make "bad"rings inside the crucible (ringing) which weaken the walls of the crucibles, making you discard them after each smelt instead of getting the more normal multiple smelts per crucible, which keeps the costs down for the hobbyist.


Then too, there is the well-known, highly respected Charles Butler Torch scorification technique which is well documented and quite "learnable." No crucibles at all...just his method, the torch he recommends, and some scorifying dishes and the tool to hold one while you are working. Pretty straight forward.

Of course, everything depends upon amounts you are working with in your smelt batches.

As far as Fluxing goes? I wouldn't use the Chapman flux if you paid me. Adding another metal as a contaminent to the fluxing ingredients just doesn't make sense to me. And Chapman's has such a metallic flux ingredient. YIKES. In fact, there have been so very many screw ups and majorly disappointed home smelters who have used Chapman's, that I created a special flux charge just to UNDO their mess ups, using Chapman's totally imbalanced flux "recipe."

I'm kinda handicapped right now as far as doing any smelting at all, even for myself, which is why I've got time to answer questions if I can. I can still smelt in the much smaller more portable units like I described above, but my larger, multi-crucible unit is out of reach at the moment.. You see, we had 44" of snow...all at once in the lower Treasure Valley of Eastern Oregon into SW Idaho since Dec 5th this year. The snow has melted, but now I have a collapsed roof to repair and can't even get into my outbuilding yet as the doorway is blocked. So, that's going to take some re-do to do it, it's so soggy and dangerous, so there's that.

Let me know if I can help. I'll swing back by and see if you've replied. If I can, I'll try to keep you out of trouble.

Oh, and yes, I do have a 4 fluxes sample kit with Teaching CD available (Windows Op Sys only.) Full color, step by step How-To and Why with my own photos. The fluxes are available in quantity after initial purchase of the teaching kit, and hand packaged by yours truly. It can be found on my website. It's been so long since I was here on this forum, I don't know what the current rules are for mentioning how to locate that specific information, and would hope Dan or Denise or one of the other moderators would let me know what's approved and what isn't before I go and break some rules with link or anything about the fluxing and smelting how-to for gold smelting in particular.

The 4 fluxes I can generally tell you about do the following:
1) Mixed together gold/mags/and non mags black sand smelt flux
2) Mixed together gold and magnetics combined blacksand smelt flux
3) Standard Assay Smelt Flux
4) The fix the screwed up results from either not following my directions, or using imbalanced fluxes like Chapman's mentioned above. (Can get 2 fixs per sample bag of this #4 flux)

Hope this helps.