Martijn
Well-known member
Maybe because his buyer can not verify the last 0.4% purity and rounds it off at .995?
We use graphite crucibles to melt.Did you XRF the dry gold sponge before you melted it to see the purity from the refining process? Are you using graphite molds or iron molds? We discussed making shot before casting ingots so you can weigh exactly to cast your bars. What does the XRF tell you about the purity of this shot before the bars are cast? First you have to determine when the iron came into the picture.
I recommend using a ceramic crucible instead.I tested with XRF some graphite powder after melting, from the bottom of the crucible.
I did a few tests from different places. In some places, XRF gave an error, but in some places it showed some base metals. Most of all showed Fe.
The pollution seems to be from here.
Some also suggested immersing the hot ingot in dilute nitric acid solution after Vaccum Furnace to remove white deposits on the ingot surface. Do you think with them?
Do you suggest a better way to melt a gold sponge than to melt it with graphite crucible in an induction furnace?
Is the conversion of pure gold into shots (granules) effective in the appearance quality of the ingot?
Ceramic crucible with gas, not induction furnaceI recommend using a ceramic crucible instead.
On the advice of you and other members, we do not add any additives to pure gold sponges when melting.I have never heard complaints of refined gold being contaminated in a graphite crucible. I googled “iron contaminated graphite” and found articles on using iron contaminated graphite to clean up polluted water from both arsenic and chromium.
This begs the question of the source of the graphite used in your crucibles.
If you melt the gold sponge in a crucible and test the bar, then melt some sponge in your vacuum casting machine do they test the same for iron? I doubt both your graphite crucibles and graphite boats are similarly contaminated.
What kind of Gas/fuel are you using?Ceramic crucible with gas, not induction furnace
,We also use graphite molds for casting in vaccum furnace.
I made a standard gold ingot and re-melted it in a vacuum induction furnace. There was no problem. Its surface became like a mirror.Maybe from process induced contaminations such as carbon in the form of soot or tar, fluxes, air leaks, outgassing, or you have oil soaked insulation, etc. Something random and not detected in the Gold with the XRF but is a contamination of the hot zone could set off a chain reaction of sorts, resulting in a reading/reaction of Fe particles coming from parts in the furnace itself because of degradation maybe.
One of the best signals I can get from dealing with a person is knowing where they stand. Remember Howard Cosell? He used to say “tell it like it is”. Never a bad thing.I' wasn't trying to be mean it's just frustrating trying to help someone who's not helping me help them!
So because your "standard gold ingots surface became like a mirror after re-melt".I made a standard gold ingot and re-melted it in a vacuum induction furnace. There was no problem. Its surface became like a mirror.
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