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Determining gold karat using only acid


#1

I was watching television this morning and the new show had a
gemologist as a guest to talk about selling gold. Two things caught
my attention.

  1. He said he had been extensively investigated by the FBI and
    Nevada authorities to deal in jewelry. My first thought was that he
    was talking about someone who’d been caught in ‘irregularities’, but
    then I realized that he was talking about himself and realized he was
    trying to promote himself. My next thought was “When did we need to
    be investigated by state and federal authorities to buy and sell
    jewelry?”

  2. The gemologist gave a demonstration on determination of gold
    karat. He had a couple pieces of gold jewelry, a touchstone, and some
    acids. There were no testing needles. The gemologist described the
    acids as 10 karat acid, 14 karat…, etc., then proceeded to rub one
    piece on the touchstone. He then applied acid beginning with 10K,
    then another. At no time did he use any testing needles for
    comparison.

So, in regards to 1., I assume he was trying to promote his business
as being squeaky clean. My question is in regards to 2… I suppose
that it’s possible, with the benefit of much experience to determine
gold karat using only acid and observing the resulting reaction, but
it goes against the grain of all education and reading I’ve had/done.
Is it common practice out there to use only acids?

Mike DeBurgh, GJG
Henderson, NV


#2

Mike -

I for the most part, only use acid. The one time I had an ambiguous
result, and retested with a comparison to a gold karat needle, the
result was still ambiguous. I told the customer I would buy “this
part” of their jewelry for $xx, but “that part” I would not make an
offer, since I could not prove it was really the gold karat as
marked.

It’s not that I have so much experience (NOT!), but that I am clear
about what my offer is. “I will buy this, this & this for $xx, but
not That”. If it passes a lower karat test and they agree to the
price, then I will buy it.

Sometimes I have a bad feeling about a thing, perhaps I lose a sale
but maybe I save some money… If it gives me the willies, (btw,
anyone a SciFi channel fan out there…remember “Farscape” Aeryn Sun
saying, “It gives me the woodie”…) it’s better to let it go.


#3

Hello Mike,

working with acid can be very accurate IF (!) you know what y’re
doing and that’s the answer.

The majority of the people - and I’m one amongst them- just do what
the inclosed small paper tell us how to do it. I’m having in front
of me a book which I bought, when I’ve been working in Germany, named
"Handbuch des Goldschmieds". I’m reffering to the second book (band
II) page 29 -35. This section clearly explains how to perform the
test talking about gold and Silver AND how to perform a test with
Fire! Now, who knows the knowledge of how to perform this test which
has an accuracy of 0,002/1000 of pure metal?

Fact is that time is money and instead of giving yourself enough
time to do it the way it has to be done. We strike that teststone a
few times with the and that’s it. We grab the acid and add some on
the goldband left on the stone…jepp it is or it isn’t dissolving
and we move on.

The big advandage of today is that almost everything is digitalized.
Just a few handlings and a perfect readout on a claer visible
display…no doughts and very quick. I had the privilage to see an
old goldsmith working with acid to essay his gold and let me tell you
that he was very accurate with his acid. I tested the same cold with
my goldtester GXL-24/pro and he was of .2 karat with his acid
methode.

Most of us lost it on our way or never learned it the from someone
else. The only comparison we have is that little written note. The
old fashion way isn’t that bad at all, it’s the person behind it who
makes the difference according to my opinion.

Merry chrismas to all of you
Pedro


#4

I have used these nitric solutions for many years to determine karat
in my studio. Just a touch stone and no needles (although I have
them).

It works great for determining which bit of scrap is 14 or 18 or
22-- or testing a client ring-- but it is not as precise as needles
and a single concentration of nitric. This relies on dilutions, I
suppose, of nitric each in its own little bottle marked 14k, 18k,
etc.

If the rubbed smudge of gold on the touchstone turns brown or fades
under a drop of 18k, it is under 18k. Then test it with 14K acid and
if it remains unchanged it is at least 14k. Might be 15k, might be
16k. In my studio it is really used to determine which bit of scrap
is which. Since I really only use 14k, 18k 22k and 24k this suits my
needs.

You can with some practice, interpolate karats in between the acid’s
rating somewhat by the degree that the smudge fades under the acid.

I suppose that the concentration changes as the acid ages but for
comparison it is fine, I think.

Andy


#5
Fact is that time is money and instead of giving yourself enough
time to do it the way it has to be done. We strike that teststone
a few times with the and that's it. We grab the acid and add some
on the goldband left on the stone....jepp it is or it isn't
dissolving and we move on. 

The problem is that acid changes over time, even if stored properly,
which is not the case with jewelers. The needles are there to warn
you of this fact. Unless you preparing fresh acid every day, the
savings of time that you are referring to are only imaginary, and
very possibly costing you more than you can imagine.

Leonid Surpin
www.studioarete.com


#6

After about so many years, you know the reaction that the acid will
give on a given karat of metal. I haven’t used the testing needles in
years. The differences of reaction… in my opinion… are sure
obvious enough to not need a proof test every time with the needles.

Dan.
http://www.dearmondtool.com


#7

We purchase bulk Reagent grade Nitric… The watered down cheap stuff
may change but in 35 years I have never seen the Reagent grade
change. We use a gallon about every six months and the last time you
take the lid off the bottle, if a dust particle floats over the mouth
of the bottle, you get a little puff of smoke as it is eaten. It
isn’t changing much if at all. We all have our methods and should do
what we are comfortable with. Our refiner never returns anything
saying we have marked it wrong and the ticket talleys perfectly for
what we have refined back to 999.

Dan
http://www.dearmondtool.com


#8

The best way I found is a portable XRF X-ray Florescence analyer.
Gives a reading to 0.01 % accuracy of what your metal. Expensive, but
worth it.

Mark Zirinsky
denver


#9

Hello leonid,

The problem is that acid changes over time, even if stored
properly, which is not the case with jewelers. 

indead but that’s is also treu with the gel used in the test
application of the GXL-24.

The pure acid’s stored in a proper cabinet will change in time
aswell. Do you refresh them every day aswell? Are they degrading
thismuch in a day, I don’t think so.

The question I answered is that testing with acid can be very
accurate if it’s done according the rule’s. If people are doing this
every day like refinners do, acid will not turn bad this fast.

According the book I’ve reffered to, one should strike the teststone
10 up to 20 times with enough pressure for a good mark which need to
be minimum 1mm wide. The teststone needs to be cleaned (there is even
an recept to clean this stone), wiped of, dry etc. It will and need
time for proper readings. I do not keep myself busy with something
else while I’m working with acids. I’ll do this 3 times and then I’m
very pleased to sell what I have because I’m very sure of my product.
Time that I use for this test is not that imaginary! That is the
point I try to make cleare. The way you answered already gives me an
idea of how most people think. Please, by all means, don’t feel
offented or insulted!

If you buy gold from someone which is marked as 14 Kt and test prove
that this gold is 13.9 whould you be pleased? It is only 0.1 kt and
the difference is not even a dollar! On the other hand, are you happy
when you lose 10 dollar per day presenting 1 gram of 14Kt gold (no
labor costs)? I whould likely spend more time having only my
customers pleased with my products then thinking toomuch of saving
time. Everybody does it his way. If one needs to perform a gold test
ones in a while then you are absolutly right, however, if goldtests
are run on daily bases, I’ll beter be safe then sorry. Customers are
very critical and they should be this way, they pay for there
products.

I’m sharing info and feel free to do as you please. These are no
rules at all.

Have a nice day and enjoy
Pedro


#10
We purchase bulk Reagent grade Nitric... The watered down cheap
stuff may change but in 35 years I have never seen the Reagent
grade change. 

I am glad that where you are, things improved that much. Here, on the
planet Earth, we still have to deal with such inconveniences as acids
loose their concentration over time, especially if stored in small
bottles.

Leonid Surpin
www.studioarete.com


#11
The pure acid's stored in a proper cabinet will change in time
aswell. Do you refresh them every day aswell? Are they degrading
thismuch in a day, I don't think so. 

No, I do not change my acid every day, and you are correct about
electronic gold testers. I bough one and I never use it, precisely
because the accuracy depends on acid concentration.

I guess the best way to answer is to describe how I was taught to do
the test.

I have 5 needles in my kit - 22k, 18k, 14k, 9k, 6k To do the test I
would do 5 parallel streaks with metal under testing. Below these 5
streaks, I would do 5 streaks, one with each needle. Acid applied
across both groups of streaks in one swipe per group, let dry,
gently washed, and examined.

Even if acid weakens, the needles give you a basis for comparison.
Without needles, you are relying on memory, but what cannot be
possible known is how the acid changed, since reaction was memorized.

As far as refiners, gold purchases, and etc… They simply protect
themselves by under-paying. It is more efficient for them and in a
long run they come out ahead. Even if some customer may ask a
question, they have plausible explanation for their practices. Very
few know exactly what is in their scrap and go to the trouble to
finding out.

Leonid Surpin
www.studioarete.com


#12
The problem is that acid changes over time, even if stored
properly, 

The acid itself won’t change (unless it’s contaminated), but the
concentration may, through evaporation.

Al Balmer
Sun City, AZ


#13
The acid itself won't change (unless it's contaminated), but the
concentration may, through evaporation. 

Picky, picky.

“Acid” was used as a colloquial term referring to prepared acid, used
for testing.

Leonid Surpin
www.studioarete.com