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Preferred metal testing method


#1

I recently needed to know quickly the approximate karat quality of a
customer’s jewelry item brought in for custom work. The acid testing
was inconclusive at first and it took reworking the acids to obtain
a consistent test result. Acids were either too strong or too weak
and I did a remix to get a reasonable time of the reactions on the
slate rub stone.

My thought was “what if we had an electronic metals tester”, meaning
the basic portable sort using a gel and wire connections to provide
a readout of quality. My employer has insisted for several years
that these testers are not reliable. Asked again a day ago, he
repeated the same disrespect for the testers. I honestly do not know
how reliable the testers are but with the unusual situation just
faced a quick and reliable test method would have been welcomed with
a hurrah!

If you have used both acid testing and the small portable electronic
metal testers, what can you tell me of reliability of test results
comparisons? Am I doing better using acids/rubbing stone/known
sample or using the electronic devices?

Thanks. Tom.


#2

Hi Tom,

If you have used both acid testing and the small portable
electronic metal testers, what can you tell me of reliability of
test results comparisons? Am I doing better using acids/rubbing
stone/known sample or using the electronic devices? 

Personally I don’t like destructive testing, and the acids are
pretty nasty.

I was trawling the web to see if there were analysis services in
Australia for custom alloys, and I came across this :-

http://www.ganoksin.com/gnkurl/14

I sort of like the point and click approach, upload data to your
computer, and the pieces are untouched.

I would assume it’s not cheap, judging by the built in security
features.

Regards Charles A.


#3
I sort of like the point and click approach, upload data to your
computer, and the pieces are untouched. I would assume it's not
cheap, judging by the built in security features. 

Yes, x-ray fluorescence is a highly accurate test so far as it can
go. Note that it tests the surface layer, not the whole bulk of the
metal, so electroplated or surface depleted pieces can fool them. But
other than that limit (shared by most other non-destructive tests),
these things can be accurate to the parts per million level.

The trouble is, they’re not generally jewelers tools. The reason?
You can buy a full featured full size laser welder for less than
these things. (the one time I tracked down a price, when one was
offered for sale on ebay, I came up with a price range of from 35 to
45 thousand dollars. That’s do-able for a major lab, or a refinery or
larger manufacturer who needs that level of in house control over
metal quality and alloy composition, or the like. But not for most
jewelers.

Peter


#4
Yes, x-ray fluorescence is a highly accurate test so far as it can
go. Note that it tests the surface layer, not the whole bulk of
the metal, so electroplated or surface depleted pieces can fool
them. But other than that limit (shared by most other
non-destructive tests), these things can be accurate to the parts
per million level. 

Once they are calibrated against the particular alloy you are
testing then they can be quite accurate but I think you will find
that refiners will not pay full value on XRF alone. Fire assay is
still the most accurate means of determining precious metal content.

James Binnion
James Binnion Metal Arts


#5

So, I gather the lean is toward acids for testing accuracy? Or not?
Sure various forms of x-ray testing are done locally in metals
purchasing yards but alas, we are a retail jewlery store. For that,
which way would you go, with x-ray out of the picture and acids
competing with the electronic (the few hundred dollar sorts, not
more) ?

Tom


#6
For that, which way would you go, with x-ray out of the picture and
acids competing with the electronic (the few hundred dollar sorts,
not more) ? 

Traditional test acids require a bit more practice and skill to use
accurately, and perhaps a bit more time to do than the electronic
meters. But comparison tests have shown that experienced workers can
achieve the same, relatively accurate results with either method.
With practice, and a proper set of comparison test needles (make
your own if you like), you can get within about a half karat with the
acids. I don’t think the meters are any better than that… But the
meters, while a good deal more costly, are a bit faster, and require
a bit less expertise to use. Either method, used incorrectly can be
way off.

Peter Rowe