Bar variation between top and bottom

snoman701

Well-known member
Joined
Oct 8, 2016
Messages
1,809
Location
SE MI
If you have a poorly mixed melt of karat scrap, how much variation can one realistically see between the top of the bar and the bottom of the bar? Say 1 cm thick.
 

nickvc

Well-known member
Joined
Sep 14, 2009
Messages
4,894
Location
birmingham
It can vary quite a lot depending how poorly the bar was melted and stirred , if you are working on tight margins which I did with a return of 98-99% you can lose money very easily , my advice is re melt stir well and pour again or drill through the bar say 3 times top first and same bottom in different areas melt the resultant drillings and scan that once cleaned, I’m assuming you are using an xrf to get your assay.
If this bar belongs to a customer ask him to come in and witness the melt and show him your results you already have so he knows why you want to do the melt , failing that offer to pay on the lowest result .
The cause of this problem is usually PGM within the melt but iron can also cause the problem .
 

snoman701

Well-known member
Joined
Oct 8, 2016
Messages
1,809
Location
SE MI
Thank you Nick!

I had a 4oz bar of average 12k that I melted, but after the fact realized I didn't really stir well. Top of the bar reacted with nitric, and I was annoyed, but haven't had time to go back to it. Figured I just bought a bad piece.

Guess I'll just inquart it to see how much gold is actually there and just how bad I screwed up.
 

Geo

Well-known member
Joined
Mar 1, 2011
Messages
6,748
Location
Decatur,Ala.
12K can react to hot nitric acid any way, although it is a very weak reaction. Depending on other metals in the alloy. Green gold has more copper and so nitric acid will react with it more than white gold will.
 

goldnboy

Member
Joined
Apr 24, 2012
Messages
12
Location
Des Plaines, IL
If you have a poorly mixed melt of karat scrap, how much variation can one realistically see between the top of the bar and the bottom of the bar? Say 1 cm thick.
When the presence of Fe and Ni are too excessive to allow proper alloying into Gold you need to make a Copper addition to the melt to assist in acheiving homogeneity. The amount will very depending on the level of these elements, but typically somewhere in the range of 1/2 the weight of the problematic bar to as much as 5X the weight of the bar (in the case heavier Fe & Ni). The problem will also occur when you have other rare metal contaminants like Ta, Mo, Cr, Co where you may find an even larger Copper addition might be necessary. Good Luck.
 
Top