# Affordable crucible question.



## yonderfishin (Apr 7, 2012)

What would you all more experienced folks reccomend for crucibles when trying to keep cost down as much as possible ? Do the cheaper "one shot" type crucibles work well for black sand smelting with a microwave furnace or is there possibility of them getting too hot and breaking down ? I see the graphite ones are rated for higher heat , but they also cost more and , while I do know the safety procedures and am no stranger to working with hazzardous processes , Im trying to put together the materials needed to atleast give this a try , but but as affordable as possible. I appreciate any info you can give.


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## MysticColby (Apr 9, 2012)

do you mean you're using an actual microwave as a furnace? or induction furnace?
either way, I don't have a good recommendation for you  (there are different recommended crucibles for each method of heating)
But if you're going to use a microwave, that's so cool!
I think I've heard of people using the sprue of a mold as the "crucible" in a microwave furnace. the whole mold goes in the microwave, and when you open it, it's only to let it cool and remove the casting.


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## Geo (Apr 9, 2012)

theres a video somewhere in the forum, i cant remember where, that shows the microwave furnace in action. the company that sells the proprietary ingredients as far as the flux goes recommends the use of the furnace for black sand concentrates.the video is cool but as far as i know, none of our members have used one. or if they have, they havent shared it with the forum.


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## yonderfishin (Apr 10, 2012)

MysticColby said:


> do you mean you're using an actual microwave as a furnace? or induction furnace?
> either way, I don't have a good recommendation for you  (there are different recommended crucibles for each method of heating)
> But if you're going to use a microwave, that's so cool!
> I think I've heard of people using the sprue of a mold as the "crucible" in a microwave furnace. the whole mold goes in the microwave, and when you open it, it's only to let it cool and remove the casting.




A kiln goes into the microwave with the crucible inside. The only kiln Ive found available to buy for this purpose is made of layers of ceramic fiber board , but I am trying to come up with a cheaper do it yourself alternative using either firebrick or clay chimney liner. The microwave energy causes the iron in the black sand to heat up , probably arcing , and will reach a temperature high enough to melt any gold present , then it sinks to the bottom. When its finished you just pour into a mold where the gold sinks below the slag and forms a button. I have communicated online with a couple people who do this regularly and have good results with the commercial model.


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## jm33 (Jun 25, 2012)

Hi, I'm also interested in using a microwave for this purpose. Do you have any update regarding your progress?

TIA, John


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## Irons2 (Jun 25, 2012)

Smelting the Black Sand is not always very efficient, no matter what method is used to heat the material. Most of the PMs remain dispersed in the black slag that results. One has to get rid of the Iron content before smelting, otherwise it just makes a mess. Not all Black Sands are the same. One has to study the makeup of the particles and devise a process plan for that particular material.

Microwave smelting is just another example of Cargo Cult Science.

https://en.wikipedia.org/wiki/Cargo_cult_science


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## Dlog Renim (Jun 25, 2012)

i found that..



[youtube]http://www.youtube.com/watch?v=tB3oQeTG-Mc[/youtube]

[youtube]http://www.youtube.com/watch?v=9qlvSY47S7k[/youtube]

[youtube]http://www.youtube.com/watch?v=-44TOyzI4ic[/youtube]

[youtube]http://www.youtube.com/watch?v=1jzKoIuFa0g[/youtube]


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## galenrog (Jul 30, 2012)

For most microwave smelting applications a fused silica crucible is best due to being microwave transparent and a thermal insulator. This lets microwave energy pass through to the contents and retains the heat produced which is held in the confined space of the kiln assembled in the oven space.

The graphite crucible is best for higher heat applications. Gas fired and induction type smelters are what I would use a graphite crucible with. The thermal conductive properties of graphite make it ideal.

Graphite crucibles should not be used with microwave smelters due to being a poor conductor of microwave energy.

Each in it's place.


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## bswartzwelder (Jul 31, 2012)

I remember that post concerning the microwave oven. It was in the build your own equipment forum under the heading of "Terracotta chimney liner for microwave kiln ?" There's even a video posted by Palladium which shows the process. Here's a link to the video: http://www.microwavegoldkiln.com/instructions

Seems to me that would be really hard on a microwave to use it like that. I would recommend buying a "disposable" microwave if you want to try this and not use your kitchen microwave. Either way, if you try it, let us know how it works. It appears you need about 3 times more flux than black sand/gold mixture. It also seems like the batches you can produce would be rather small, especially if you have a couple hundred pounds of black sand to process.


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## bswartzwelder (Jul 31, 2012)

Just looked it up on their website and the basic kit was $269.00. If you want a cone mold, the kit is $343.00. The flux is $29.00 for 5 pounds and $75 for 15 pounds. Again, if you go this route, let us know what your results are. It sure would be nice to know what makes up their flux. I'm sure you could make it yourself and cheaper than what they sell it for.


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## Meh1 (Aug 23, 2012)

This might be a good place to post a similar question...Ive read from a few separate sources that you can use a potato as a crucible...basically cut the potato in half...use a spoon to make it a bowl...use a propane torch to cover the exposed potato with carbon (burn the potato)...then put your material to melt in the center a little at a time...anyone ever tried this?...pros...or cons?


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## butcher (Aug 23, 2012)

Meh1,

Old miners used the potato to remove mercury from amalgam gold (a dangerous process).

It would not work good for melting your gold (too much moisture).

Wood although has moisture even in old dried wood would make a better choice if your melting gold in a cave.

Melting dishes are so cheap and easy to get why take chances with such an expensive metal, just spend a couple of dollars and get a melting dish, spend ten dollars and buy several at once, this way you can melt thousands of dollars of metal with no problems.


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## NoIdea (Aug 24, 2012)

Evening All, now, i've read through the thread and did not see mention of the composition of the flux used, i apologies otherwise. 8) 

Silicone Carbide is a very strong microwave receptor, gets really really hot.

If a flux swells, the chances are it contains compounds such as carbonates, borax, and moisture, well those are the ones most common to me; could even contain calcium fluoride.

Probably has something to do with why they stir the mix during the melt. 8) 

Deano


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## nh6886 (Sep 9, 2012)

Good Morning,

Maybe one of you can help me with the math on something like this. At six dollars a pound for the flux and needing to use three times the flux as black sand your looking for black sand that Assays around 21oz a ton at $1700 gold to break even? If anyone out there needs help shoveling black sand like that I have a shovel and I'll pick up a spare on the way.
I must be doing this wrong. I have been saving my blacksands for some time and I have a couple hundred pounds that some day I will figure out what to do with. I'll add for clarity that it all came prom panning my cons off a highbenker and sniping.

All the best,
John


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## bswartzwelder (Sep 10, 2012)

I, too, have a few pounds of black sand. I have crushed mine into a talcum powder consistency and will be adding it to my microwave gold kiln at some future time. I wish there was some easy way to get rid of some of the black sand which doesn't contain gold. Someone said citric acid. May have to check in on that before i waste a lot of time and money on flux.


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