How to build a Gas Furnace – Melting Gold and Silver (DIY)

How to build a Gas Furnace – Melting Gold and Silver (DIY)

Hi everybody, In this video I’ll show you a small gas fired
furnace that I’ve built with relatively cheap and easy to find
materials. Warning, Operating a gas furnace and handling molten
metals can be extremely dangerous and might result in a serious injury or even death. Beside the obvious fire risk, a gas furnace
should only be operated in a well-ventilated room or outside to avoid exposure to high levels of Carbon Monoxide
and other harmful gasses. Let’s start with the furnace’s outer shell:
as you can see ľ it is made of a simple steel pail cut about a third from the top. The burner hole is cut on the wall of the
bottom stationary part of the furnace and another hole is cut at the middle of the furnace
cover. Both parts of the furnace are fully lined,
top to bottom with 2 inches of ceramic fiber insulation blanket. On the bottom there’s an insulation brick
to provide a stable footing for the crucible. All of the insulation is rated for a working
temperature of 2300 Fahrenheit. A roll of one inch thick insulation blanket,
2 feet wide and 23 feet long – cost me about 60 bucks and I only used about 3 or 4 feet
of it for this project. Now, let’s go over the burner setup: I’ve
place a regular torch on top of a small DC servo blower. The valve on the torch is used
to regulate the gas flow. The blower speed is regulated by a laboratory
power supply. The final piece is the burner itself. It is
basically a half inch plumbing pipe fitted with a one inch to half inch reducer that
acts as a flare. There are basically three types of flames
possible: reducing flame, neutral flame and oxidizing flame. Without drifting too much into this subject,
each type represents the gas to oxygen ratio flowing through the burner at any given time. A Reducing flame is such when there’s more
gas than the available oxygen could burn. It produces lower temperature and is usually
recognized by a hissing sound. An oxidizing flame is exactly the opposite,
burning very hot and produces a roaring sound. Neutral flame is when the ratio is just right,
meaning there’s exactly the right amount of oxygen available to burn a given amount of
gas. It is also called the “stoichiometric point”. Here’s the crucible I’ll be using for this
melt. To produce shot, I’ve drilled a few holes into the wall of the crucible so that I could easily pour the molten
metal into a bucket of water. And here’s what I’ll be melting today, there’s
about 8 pounds of pure silver in there. This silver came from an electrolytic refining
process. And in case you were wondering it is 99.99 percent pure. The crucible is placed in the furnace, right
in the middle. And the furnace is lit up. It is important to start the furnace with
the lowest setting possible in case there’s some left over moisture in the melt or the crucible material itself. Ceramic
crucibles can also suffer thermal shock and crack if heated too fast, even if it is completely
dry. I’ll put the cover back on and let it do its
thing. Here we are about 5 minutes later. Everything
is red hot, as it should be. About 13 minutes in to the melting process,
all of the metal is molten and ready to be poured. Hold onů If you thought that was coolů check
out this next footageů. Here’s the final productů This is of course not a perfect design, so
if you have your own furnace, take a video or some pictures of it and post it here in
the comments section below. That’s it folks, hope you’ve enjoyed this
short demonstration. Please comment, share and subscribe.


  1. In the second video the sound did not play what was the white powder you added to the gold aqua regia solution?

  2. Shouldn't the shot have formed nice round spheres?  Some of them looked mushroomed.  I think I read somewhere that you have to get the distance right between your pour and the water so the metal has time to form a sphere before it hits the water.  Still, pretty cool!

  3. Hi, excellent! , Who crucible recommended me for this: silica? fused silica? alumina? or other?, one which does not crack and good heat resistance….regards. Pablo

  4. How much did the blower cost you? I would like to make a furnace like this for my father, we mine gold and we want to build a furnace so we don't have to send the gold off.

  5. How did you secure the Carbon Insulation Blanketing to the interior of the Shell? I'm using a Propane Tank I found and modified with an angle grinder. 

  6. What type of gas are you using in that furnace.  I am new to this and have yet to find a combination that works NEARLY as well as what you have made here.

  7. If you were making a mold or… say.. A sword blade.
    Could you pour the metal into a mold that is in the water (with the mold being stable, of course)?

  8. That was awesome. Why don't you make like your own little bars or something. ? That be cool to see. And you could make your own stamp for Cool video either way and thanks for the info on the flames. Reducing, Oxidizing, Neutral.

  9. I was thoroughly pleased by watching this video, you are one of the coolest guys I know. I really like how this furnace is basically a torch rig, very cool.

  10. great videos very informative I wish I knew where you got your silver from. scrap doesn't tell us a lot you just have a lot of it. again great video

  11. I am a furnace operator by trade. I was wondering what gas you are using and the power setting for your servo. Thanks.

  12. How do you manage to hold the insulation blanket to the wall of the furnace ?
    Btw, I read 13 minutes but I hear 30 minutes, wich is the correct time lapse before pouring the melted silver ?
    Thank you for posting the awesome underwater footage

  13. I have a question that may seem silly, But with that pure of Silver, Why do you make shot instead of Bars ?? Forgive my lack of knowledge I have not yet smelted any Silver !

  14. That was cool, been studying for a couple of years on everything gold. Thanks for the information you have given. Some of the best so far.

  15. From what is made of the crucible you used in casting, a tip if you are to make casting steel or platinum you should not use a clay graphite crucible as it would glaze and pierce you should use a pure graphite crucible or crucible of tungsten but in this case you run the risk of contamination of the material due to tungsten is better to use a pure graphite crucible if you want purity in the material but in case you want durability you can can use a tungsten crucible but in this case you will get reduction in purity as tungsten oxidizes when it warms and falls on the material you are using contaminated material.

  16. By adding a bunch of crushed Ice and pouring the silver about 2 ft higher up you will get a lot better result. Not that it really matters a lot as it all gets remelted again eh. Good post fella.

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