# Crucibles - and contamination



## overdriv (Nov 2, 2010)

I have tried to reserve one crucible for 24K only but I always mess up and contaminate that crucible with lower grade like 20K. 

1. Will I contaminate my 24K with whatever is in that crucible if I use it for my next 24K batch?

2. Is there a way to clean the crap out of the crucible and re- borax it?

3. If I grind the crucible, is that dust a danger to my lungs? (Have dremel, will travel.)

Thanks guys.


----------



## nickvc (Nov 2, 2010)

1. Yes unfortunately.
2. You can try but the flux sticks well to the crucible!
3. All dust is bad for your lungs but I don't see this been to bad so long as you do it outside and don't breathe it all in but I think it might ruin your crucible!

Tip....write on your crucibles with sticks of chalk ie.24 k. Mixed karat etc. Saves so much time and you know which crucible is which even after multiple uses :mrgreen:


----------



## Harold_V (Nov 2, 2010)

I'm assuming you're talking about a melting dish, not a crucible. 

Melting dishes can be restored to like new condition by adding soda ash and heating. Any metal that is contained in the existing flux will be discharged with the molten soda ash. 

I have discussed this cleaning procedure in the distant past. You may have success doing a search on cleaning melting dishes. There's a little more to the process but I am short of time and can't elaborate at the moment. 

Do be advised that soda ash is very aggressive and will liquefy a portion of the dish. Thinning results, so you can not clean a dish endlessly. 

Harold


----------



## overdriv (Nov 2, 2010)

Harold_V said:


> I have discussed this cleaning procedure in the distant past. You may have success doing a search on cleaning melting dishes. There's a little more to the process but I am short of time and can't elaborate at the moment.
> 
> 
> 
> Harold




I looked up your posts..



By Harold (the Greatest- and humble too) (that comment by me- overdriv)


Borax absorbs oxides, yes, but when you reduce them with soda ash, they're put right back in your gold. You can see evidence of that by cleaning what you think is a dish that contains no metals, but is covered with dirty borax residue. Introduce soda ash and heat the dish well, until the soda ash starts dissolving borax. As it liquefies, you'll notice tiny beads start to appear everywhere. That's the oxides being reduced to their metals. 

In order to clean melting dishes, you have to get them to red heat, and it helps to do a little stirring with a carbon rod to mix the molten soda ash with the old borax. You may even have to pour the entire mess off once and repeat the operation. It works, and works well. I've cleaned countless melting dishes that were beyond use without the cleaning operation. The cost of cleaning is well repaid by recovered values. 

As for cupels, I don't have an opinion. They work very well for absorbing unwanted substances, but they're not generally the tool of choice for refining. They are used, primarily, to absorb lead from assays. Lead, introduced as litharge, oxidizes the charge, reducing the litharge to lead, which acts as a collector. the resulting button is then run in a muffle furnace on a cupel, where the lead is once again converted to litharge, and absorbed by the cupel, along with oxides. They have a capacity, which, once filled, renders them useless for their intended purpose. They may still be good melting dishes, but they will no longer absorb contaminants. 

Without refining by some means, the gold extracted by these stripping systems will be of questionable quality. Melting in a cupel is one way to improve your gold, as Steve has so nicely demonstrated, but it's cumbersome when you get involved in large volumes of gold. 

The material that comes from these cells is perfect for chemical refining. A boil in nitric to remove unwanted traces, followed by a boil in HCL, then dissolution with AR. The resulting gold should be of excellent quality, likely 9995 or better. 

It seems like a long, hard way to go, but it is routine, and happens much quicker than you might imagine. As you progress in extracting, and find you're producing gold in larger and larger volumes, you might keep the process in mind. 

Harold


----------

