Assaying different types of metal at high volume

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autumnwillow

Well-known member
Joined
Apr 1, 2010
Messages
447
If you were to buy gold from different people with the amount of gold/silver being sold at 0.5grams to 500grams.
What would be your preferred method for assaying the material?
With a consistency of around 10-20 clients per day.

I'm thinking XRF but its expensive! Heh
 
.5 gram? Half a gram? An assay sample is bigger than that? To start off you need to figure out the cost of determining the value and apply it to each sample you have to process. For example if it is by fire assay, it will cost you more than a half gram of fine gold to run. Plus you will need at least .775 of sample to assay gold and silver by fire assay. What I am getting at is there is a minimum amount you have to charge just to cover the cost of analysis. Depending on the method that will vary.

If you are choosing expensive XRF, the cost per analysis is very very low but the instrument cost is high. If you are choosing fire assay, the cost per analysis is considerably higher in time and expendable supplies but the setup is less expensive. Finally if you are choosing to do acid scratch testing, if the material you are buying lends itself to that type of testing, your cost per analysis will be less than fire assay but time consumed will exceed the XRF.

Based on what you asked, I would be honing my scratch testing skills, especially for the very small lots.
 
Given you are talking a range from 0.5g to 500g and up to 20 clients per day I would be spending the money on the XRF, and then a little more to learn how to use it properly i.e. Knowing how to read spurious readings and discount the errors you can get by using it incorrectly.

Getting your assay wrong on a 500g lump of metal could cost you more than a decent gun alone.

Think big, don't think small.
 
anachronism said:
Getting your assay wrong on a 500g lump of metal could cost you more than a decent gun alone.

Excellent point.

For the small lots, a touchstone or just a quick nitric spot test could get you in the ballpark. But, if you are talking pounds of karat, then it would certainly be in your best interest to pony up the cash and get the xrf gun.

Everyone makes bad buys every now and then, but, to make a bad buy on over a pound of gold would probably be the last nail in the coffin for a brand new business (unless they have a backer with deep pockets).
 
Okay. I'm saving up for XRF then. I'm actually using touchstone at the moment.

Fire assay would not be ideal as it is too slow. This is good for large lots though.

For XRF, I would melt the entire material, mix well and pour in a mold to avoid thick plating scams.
 
I have a client who buys a lot of coins and bars and until now he was forced to open each plastic jacket and melt the coin before using his XRF. So he lost the premium he could re-sell at on packaged coins. He bought one of these testers from Sigma Metalytics and it does pick out the counterfeits. He demonstrated how it is calibrated with good coins and then put some known counterfeit on and it caught every one. This is the instrument.

IMG_3432.jpg

and this a photo I took of the operating instructions.

IMG_3433.jpg

The thing costs around $1000 US Check out the details on their website. http://www.sigmametalytics.com

If you buy a lot of coins this may be a valuable tool. I only know what my client said about the instrument which was favorable but I have no working experience with it. It would be interesting to hear from a few of our coin buying members to see if they have first hand knowledge.
 
Whats the technology behind it?
I think its just measuring the density of the material. Good for high karat gold but not for low karat gold.
 
autumnwillow said:
Whats the technology behind it?
I think its just measuring the density of the material. Good for high karat gold but not for low karat gold.
It looks to work on the magnetic field.
"Using electromagnetic waves that penetrate deeply into the coin or bar, plating and surface features are largely ignored, and the main body of metal assessed. The Verifier can see through plastic cases and bags, so numismatic coins do not need to be removed from protective holders."
All elements have a magnetic signature.and varying reactions to magnetic influence.
There should be a P.C. application and USB interface some where that can do the same job.
Being that magnetism is such a well studied subject there should be some quite efficient projects documented.
I would be concerned that some alloys might display similar traits to our target elements.
 
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