# Cast Iron Crucible?



## Avery (Oct 29, 2020)

Is there anything (borax for example) you can "coat" a cast iron crucible with to make it useable for melting gold and silver?


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## butcher (Oct 30, 2020)

You can melt silver using a reducing flame to soot the iron crucible (burning a layer of oil into the iron mold or melting pot will work similarly to put a layer of carbon soot on the fixture), silver and iron will not alloy in the melt. Basically, you can melt silver in a greased iron skillet. Although a ceramic melting dish, crucible, or cupel would be better, they are cheap and are much more suited for the tasks.

Forget about melting gold with iron or in a cast-iron crucible, one metal will become a solvent for the other metal and the two metals will make an alloy together, ceramic melting dishes or crucibles are cheap and readily available...


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## Avery (Oct 31, 2020)

Sounds good. I just happen to have some pretty cool cast iron crucibles and was trying to figure out a way to use them. And I have around a 20 qt. cast iron dutch oven I was hoping to use when I hit the big time..


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## kurtak (Oct 31, 2020)

NEVER try to melt gold in cast iron (or any kind of iron) mold/pot or crucible) molten gold acts like a "solvent" of the iron & will therefore cause some the iron to dissolve & alloy with the gold thereby contaminating your gold - nor should you use iron as a mold for pouring gold into

Because of the lower melting point of silver you can get away with melting silver in cast iron --- however - I "do not" recommend doing the actual melting in cast iron - you are better served using a normal crucible for the melt then pouring the silver to the cast iron mold

The cast iron mold NEEDS to be hot & it (the mold) must be coated with a layer of carbon - if you don't coat the mold with carbon the silver will stick to the mold & you wont get the silver out of the mold

I put my cast iron silver mold on a camp stove propane burner - cover the bottom of the mold with a 1/16 to 1/8 inch of olive oil & let it smoke until the carbon (from the smoking) has coated (fully) the inside of the mold with carbon then pour the silver to the mold

Or - if you have an oxy/acetylene torch set up you can turn on ONLY the acetylene - light it - & "soot" the mold with the carbon from the burning acetylene

Kurt


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## nickvc (Oct 31, 2020)

Another way to coat your mold is to spray it with WD40 when hot that also works really well 8)


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## snoman701 (Oct 31, 2020)

nickvc said:


> Another way to coat your mold is to spray it with WD40 when hot that also works really well 8)


I like that!!

I brush on oil, but it always burns the bristles if it’s still hot. 


Sent from my iPhone using Tapatalk


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## Deano (Oct 31, 2020)

In large scale commercial use the moulds are either brushed with a commercial release agent, usually contains titanium oxides or similar, or just sprayed with WD40 as Nick said. Applying carbon from an oxyacetylene flame works but is not as practical for large scale use.

Note that all release agents are sacrificial, they need to have the mould cleaned and the coating reapplied for each usage.

The most important point in using a mould is to ensure that it has no moisture on the pouring surfaces, usually the mould is preheated on top of the furnace before use.

Deano


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## snoman701 (Oct 31, 2020)

Deano said:


> Note that all release agents are sacrificial, they need to have the mould cleaned and the coating reapplied for each usage.



What's the best way of cleaning an iron mould once you end up with the small piece of slag that won't let go sticking in the corner? 

I generally go at it with a cape chisel, but it can't be the best way for sure.


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## Deano (Nov 1, 2020)

Commercially the cleaning is done with an air powered needle gun, the smaller the mould the more difficult complete cleaning is.

Deano


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## snoman701 (Nov 1, 2020)

Makes sense....I haven't had a mould really clean since I used a needle scaler on it.


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## nickvc (Nov 2, 2020)

Another trick with a mold to clean it is to heat it and then dip it in cold water that usually shatters any flux off the mold.


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