The xrf Mystery

[Lobby]

One of the refiners in town buys gold filled jewelry.

Since GF jewelry is normally around 2% gold, and it can vary all over the place, the refiner MUST have standards in those concentration ranges to pay accurately. Or, to make sure he doesn't overpay. :mrgreen:

The GF jewelry I've melted has copper as the major component, but there's lead and tin there also, in addition to the gold.

 

[Pauleames]

benign01,
We own a Niton XRF machine as well and the same thing happened to us. Our refiner used to drill on both sides of the bar and we would get bad readings, usually 2% lower. However they did melt all bars prior to the XRF analysis and then would make one larger bar, then the drilling would happen. So we decided to change refineries and explained our situation with the old one and they said something like drilling is an old method and is not as precise. We have been using this new refinery for some time now and they first melt everything together to make one larger bar, they mix everything up and use a Pin sample. (Which we also use back home). With that pin sample an initial essay is done with an XRF machine and accept part of the payment until the complete essay is done with a fire essay. So we can compare our results from theirs and when the fire essay is done there usually is a higher difference of 0.2-0.35% difference of the initial analysis and we get payed the extra amount.
So I believe it might have to do with the shavings. I also remember that when we bought the XRF our rep in the factory told us that air between the gold and the gun could make a difference. I don't know how accurate that is, but every time we test gold we put it as flat as we can.
Hope that helps.

 

[fasTTcar]

I am still learning, but so far, my XRF numbers are always accurate to the second decimal point of what i get settled out with from the Royal Canadian Mint.

We only use pin samples, you can mess with bar readings pretty easily.

 

[Dan Dement]

Fasttcar & All,

I have jewelers who do not like to use my induction melters but prefer to use a torch. When you torch melt metal, I seen as much as 20% difference from one side to another. When you melt metals in an Induction Melter, usually you have have a 2-3% difference in reading all the sides. Pulling a pin sample from a running IM is fairly accurate. However, as soon as por the metal into a mold, the stratification and solidification starts. Every notice how the top of the bar starts out smooth and then forms a "bread loaf" effect with the top having a dip in it. Zinc & copper really moves around in the cooling process which makes getting a true average difficult. I pour my bars in a wedge my tilting the ingot mold at an almost 45 Degree angle. This method helps push the lower and higher reading to a constant. By running 7 readings on all the sides and comparing it to SG readings, you can get a very good average which is a constaint fair payout. With well over 100 payouts using this method, I am well within a $500 window on over a million dollars.

All I say is that it works for me.

Dan

 

[4metals]

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