Using a crucible - Correctly

[pokermandown]

I started down the road of gold refining because I had a veritable gold mine in old computer equipment. I decided my goal was to create a 1oz. gold ingot and then after that I would go for profit. More than a year later, I have at least 31 mistakes under my belt but over 40 grams of orange-brown dust that is really only beautiful to the folks on this board. I would like to turn 31.1 grams of it into a nice little ingot that would be beautiful to everyone.

I figured based on the learning curve of each step up to this point that I would start with some practice melts. I used propane to heat the crucible. I seasoned with it borax just like Steve does in his video. I took 1 oz of the scrap sterling I have and cut off any loose ends or solder I found and used it in place of gold. I heated the crucible with propane. I brought in my MAPP/Oxygen torch after smoking my graphite mold, and got a 1 inch tight blue flame and melted the silver to a beautiful red glowing blob. I kept the heat on it as I poured it into the mold. I grabbed the mold with channel locks and tapped the channel lock on the side of the galvanized bucked full of water I had near by. A satisfying sizzle and then voila! But no...Frankenstein is better looking. I thought maybe it was just because it was the first time I used the crucible, so I tried again.
Crucible looks not so good


Top and Bottom of ingot from the mold:



1st one is on the left and the second is on the right. While the result was ever so slightly better, it was not at all the beautiful result I was looking for. So I need to turn to you. Any ideas on what failed to do or did wrong. Any suggestions?

Thank you
--PMD

 

[g_axelsson]

When melting base metals something called a dross forms on top of the melt.
https://en.wikipedia.org/wiki/Dross
It is made up of oxides and floats on top of the molten metal. If it isn't removed before casting it will contaminate the bar instead.

Melting sterling silver is 7.5% copper and it will produce a lot of copper oxides. To remove the oxides you could use borax or maybe some other flux to absorb the oxides but it will always oxidize a bit when you cast your bars.
Jewelers are talking about fire scale and traditionally used hot sulfuric acid to remove the dark oxide.

Göran

 

[FrugalRefiner]

Sterling silver is 7.5% copper. When you melted it, some of the copper was oxidized. That's what stained your dish and your ingots.

Dave

Edit to add it looks like Göran posted while I was typing.

 

[kernels]

Ironically, melting pure-ish gold is actually quite easy compared to what you've done.

 

[nickvc]

Ironically, melting pure-ish gold is actually quite easy compared to what you've done.

I totally agree.

Melting is almost as much of an art as a science and the same applies to recoveries.
You will either learn it or not, practice is good and with it you should improve your skills but some never really master it.
Fine metals are easier so try using some refined silver to practice on.

 

[anachronism]

Ironically, melting pure-ish gold is actually quite easy compared to what you've done.

I too agree with Kernel's comment

If you're getting bars from "dirty" silver like that then you should have no problem with your gold. I don't think you failed at all, I think you were melting a dirty product.

Good luck and enjoy- you're on the right track with what you have done.

Jon

 

[pokermandown]

Thank you for the confidence. The results look pretty good! 1 oz and 1/4 oz, but I need to keep the torch on the top a bit longer I think.

 

[kernels]

Actually, those deformities on the top seem to be happen consistently when melting reasonably pure gold. They are probably a good sign. I'm sure some of the more experienced members will be able to give some better explanation as to why that happens.

Little bars are looking good!

 

[upcyclist]

Dig around on the forums here with the search bar and you'll find some other tricks people use to get their ingots and buttons nice and shiny, like sooting the ingot mold and making sure the mold is hot before you pour.