Comparrison assays to 3rd party referees

J

JDmead

New Member
#1
#1
I've been working for awhile now on getting my assays to be very accurate. When we perform a melt of scrap jewelry and draw a pin sample, I get about a pennyweight, and a 3rd party assayer gets a pennyweight, then the bar goes to a refiner. We compare the 3 results. The one from the 3rd party assayer is what I have been asked to get with in .1% of. I'm wondering if .1% is a realistic goal. Even the refinery we send to doesn't always get within that range (about 50% of the time). However, if they are off by more than .1% they are willing to accept the referee's measurements and adjust they payout.

We are looking to use my assay results to pay out to those we buy larger quantities from, IF I can regularly get the desired range of results. It improves turn around time, as it takes me about 2 days for me to perform an assay, while we don't get results from the 3rd party from, often times, well over a week.

I'm just trying to figure out if my .1% to .3% variances are really that far off realistic expectations. Is it reasonable to expect two, or even three assayers to get near identical results on a consistent basis?

AND, if it is to be expected...what the hell am I doing so wrong that my results are off as they are. (I'm not going to get into specifics, but maybe in another thread I may list my procedure to see if there is something I'm doing wrong that anyone can notice) Interestingly enough, I average about 50% of the time as well as being under .1%.

Any help is appreciated guys.

Thanks
 
fireguy

fireguy

Supermoderator
#2
#2
JDmead said:
I've been working for awhile now on getting my assays to be very accurate. When we perform a melt of scrap jewelry and draw a pin sample, I get about a pennyweight, and a 3rd party assayer gets a pennyweight, then the bar goes to a refiner. We compare the 3 results. The one from the 3rd party assayer is what I have been asked to get with in .1% of. I'm wondering if .1% is a realistic goal. Even the refinery we send to doesn't always get within that range (about 50% of the time). However, if they are off by more than .1% they are willing to accept the referee's measurements and adjust they payout.

We are looking to use my assay results to pay out to those we buy larger quantities from, IF I can regularly get the desired range of results. It improves turn around time, as it takes me about 2 days for me to perform an assay, while we don't get results from the 3rd party from, often times, well over a week.

I'm just trying to figure out if my .1% to .3% variances are really that far off realistic expectations. Is it reasonable to expect two, or even three assayers to get near identical results on a consistent basis?

AND, if it is to be expected...what the hell am I doing so wrong that my results are off as they are. (I'm not going to get into specifics, but maybe in another thread I may list my procedure to see if there is something I'm doing wrong that anyone can notice) Interestingly enough, I average about 50% of the time as well as being under .1%.

Any help is appreciated guys.

Thanks
Click to expand...
Very good questions. Not necessarily easy to answer, but here are some ideas:

When comparing bullion assays with another assayer you should be running a CORRECTED UMPIRE bullion analysis. This requires doing an initial preliminary assays and then running a corrected bullion assay which requires running a proof bullion analysis. The proof bullion analysis is an artifical sample of the same composition made up of high purity silver and gold and copper which is used to determine the losses/gains which need to be corrected.

Volume II of the SMA Methods Manual has a good discussion and method for running bullion analysis:
www.lmine.com/product/9051x.html

Testbooks of Fire Assay by Bugbee and Shepard & Dietrich also are good references for this:
www.lmine.com/category/assaying.html
 
J

JDmead

New Member
#3
#3
When performing the assay, I have 3 samples from the melt, each about .5g as well as a known piece of .999 Au that I run at the same time. From my understanding the result of the known Au is then used to make the adjustment to the others. Is that correct?
 
fireguy

fireguy

Supermoderator
#4
#4
JDmead said:
When performing the assay, I have 3 samples from the melt, each about .5g as well as a known piece of .999 Au that I run at the same time. From my understanding the result of the known Au is then used to make the adjustment to the others. Is that correct?
Click to expand...
No, that is a bit over-simplified.
Here is the rough process:
1) do a quick bullion analysis so you know the approximate composition of your material.
2) run the actual sample, and along side run a PROOF. The proof will be an artificial sample of the same composition as your actual sample made from high purity gold, silver, and copper.
3) calculate the losses or gains of gold AND silver.
4) adjust the final numbers of your samples run to correct for these gains and losses.

The adjustments are substantial enough that you will not match the refinery or the umpire if they are not corrected.
 
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