How Can One Eliminate Craters on Button

[chemist]

When melting a gold button in a crucible, the button always seems to have craters on the bottom side. The top is beautiful and smooth with a dimple in the middle, but the bottom looks like the surface of the moon. Is this normal? Why does this happen and what can I do to get a smooth-bottom button?
The gold has been through the poor man's AR process twice. The flux is borax. Melting is done with a fuel-oxygen torch.

 

[Lou]

Do it in a smooth bottom melting dish, well seasoned with a thin layer of borax. There's no easy way to flame polish gold buttons unlike platinum and palladium (flip over a crucible, put the offending button nasty side up, and then go at it with H2/O2).

Your gold may also be of suspect quality.

 

[chemist]

Although I haven't had the button assayed, I am quite sure that the quality is not suspect. The dimple on top shows nice crystal planes and the color is right. I am hoping to send a sample to GSP for assay soon.

 

[butcher]

could your crucible be too cool (in melt) and would heating it during melt help?

 

[lazersteve]

Heating the button until fully molten and moving it around the dish as seen in my avatar to the left can help release any trapped air bubbles or gasses that may be under the button. If the button cools with these 'gas pockets' under it, or if the gold does not become fully molten you will get the crater effect.

Steve

 

[chemist]

Thanks, team. I reheated the button today a few times and concluded that the answer is more time. The first time that I tried it, the flux and the button were both melted, but everything was still too cold (as if 1000C can be called "cold"). On the third attempt everything was allowed to soak at high temp with the torch for a minute after it melted. The crucible was very hot, the flux was very liquid and the button turned out to be smooth and beautiful. Thanks.

 

[dick b]

Great:

Now you need to show a photo of it in the gallery section.

Keep up the good work!

dickb

 

[chemist]

I will post a photo as soon as I figure out how to get a photo in a post.

 

[dick b]

Chemist:
Steve fixed the link and there are others in the Usefull tutorials section that you can look at.

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=69&t=557#p4715

Thanks Steve.

dickb