sodium nitrate effect on gold melt

[irvtemes]

when I sell my jewelry scrap to one of my large sources they add borax and sodium nitrate to the liquid gold with a large metal scoop , I am assuming this process is to their advantage and not mine.........am I correct?

the pin sample is taken of the liquid gold of which all karats have been mixed together and not only is the original non-gold portion still in the crucible but the amount of non-gold product in the crucible has been increased by the borax and sodium nitrate. When they take the pin sample I can see stuff swirling around the top of the cruicible , I assume this also is not helping my assay as it becomes part of the pin sample..........am I correct?

Thank you all for your kind assistance.

 

[jason_recliner]

In short, no.

Borax is a flux for melting.
Sodium nitrate is an oxidiser which may help burn off a few impurities.

Neither of these compounds will alloy with gold and therefore will not affect your assay negatively.

 

[4metals]

When a pin dip is immersed in the melted metal, the small bubble on the tube melts first and the vacuum inside the tube draws in the metal. This is usually sub surface metal as, if the pin is too close to the melt surface, it will draw in air and flux and not produce a nice solid sample. So if your sample is nice and solid you have no worries.

Why a refiner would do this is questionable. The oxidizer in the flux will, to a small extent, remove base metals and retain them in the flux so in theory it will raise your assay and lower your weight but the same quantity of precious metals remains. In any event you should be asking them to bag up your slags for you to take with you. Most karat melts will retain beads of metal which all refiners do recover. So take it.

 

[g_axelsson]

I don't know how fast nitrate works in a melt, but if it takes some time to oxidize the base metals then either let it take it's time to work or pour the ingot just after the pin sample is taken.
If the metal is allowed to keep oxidizing after the pin sample is taken then the ingot will have a higher amount of gold than the pin sample. It's the same amount of gold but lower in weight.

I have no idea of how big this effect is and it is probably negligible.

Göran

 

[4metals]

The effect is neglible but if a relatively pure bar is poured this technique can clean up the bar but it has it's limits. It is an age old technique called toughening.

It is wise to always pour the melt as soon after a good pin is removed from the melt.

 

[alexxx]

In any event you should be asking them to bag up your slags for you to take with you. Most karat melts will retain beads of metal which all refiners do recover. So take it.

This is important. You will know right away if you are dealing with someone reliable who wont steal from you. From the look and the tone of your karat buyer when you ask for your slag back.

If your buyer doesn't want to give you back the slag or tries to convince you otherwise, you are most likely dealing with someone trying to scoop from the top...