Torch melting vs Oven melting. Which are better?

[ItsJayBirds]

I have gold melting torch and I'm melting jewelry, 10K gold and 17K gold.
I calculated the 10K gold usually lose about 3-5g and the 17K gold lose about 1-2g.
I never used a melting oven before. Is it any better? I know you have to change the crucible after around 10 heavy uses. I see a lot of people use oven before and it seem better than torch.
If you disagree, and think torch is better, can you explain why and do you have any tips to reduce the amount gold lost during the melting process? Thanks in advance!

 

[Elemental]

Good Morning,

I use a melting furnace (https://pmcsupplies.com/tabletop-quikmelt-30-oz-pro-30-melting-furnace-stainless-steel.html) with a graphite crucible for silver melting, my loss is under 1g per 250g ingot pour of two-nines silver to make anode bars for my electrolytic cell.

You're correct about replacing the crucible every 10-15 pours. The key is to reduce the crucibles exposure to oxygen, i.e. do not allow your crucible out of the furnace for extended periods while heated, don't leave the lid open on your furnace during cool-down, etc.

I've attempted using a small map-gas/oxy torch but didn't have much luck with larger melts in a silicon crucible. An oxy-acetylene torch is on the wish list or better yet a used scientific furnace which reaches melting temps that I can put my dishes in.

As for reasons for melt loss, care needs to be taken not to blow any material out of the dish, plus any slag from other metals in your melt.

Here is a note from an old reddit post (https://www.reddit.com/r/Silverbugs/comments/4k6fts/how_much_silver_if_any_is_lost_in_the_melting/)
"The first is sticking - it is almost impossible to get every drop of silver out. Also, if you use a torch to melt, the pressure of the gasses will fling microscopic size pieces of silver out of the bowl. It's referred to as the 'angels share' and can cost you anywhere from 0.5 to up to 3% of your silver if you are not careful. Lastly, 0.999 silver still means 0.001 other, which over 10 oz is 0.311 grams. If the other is a metal say copper, it separates from the silver with a quick melt and is either removed as slag or when you go to pour your bar it's just enough to look like a small stain on the bar. Most people polish this off so even if you don't have the problem with the other two things I mentioned, this one will result in you having just a hair under 10oz."

If you don't mind me asking, why are melting your gold in an impure state? I would recommend a chemical refinement first, and then melt your refined gold/silver to only have a single melt loss. Carat gold has silver as the filler, along with zinc and copper, if you didn't know.

Hope this helps.

Elemental

 

[nickvc]

One explanation that leaps to mind looking at your loses is that you are oxidizing base metals when you melt, there are more base metals in lower carat gold alloys which means your loses are more, chances are the gold content will increase, if you assay your materials you should be able to prove this easily enough.

 

[1mysurveymail]

adiabatic flame vs ? One process adds oxygen, the other does not. I cannot answer this question directly (since I don't know), WITH A DIRECT ANSWER, I would ask the pros. It seems blatant to me that a torch adds oxygen (and causes oxidative loss (no matter how small)), and an oven does not, although your choice of flux MAY. Straight questions, like yours, deserve straight answers from people HERE who actually know...

If, on the other hand, you are INDIRECTLY asking about whether to choose an electric vs "fuel fed" furnace, the easy answer is that electric things have components that wear out easily. A gas fed melting device, not so much... just do not take an answer from someone selling an electrical appliance without asking a "gas fed" person.