Does Anyone Have A Sigma Metalytics?

Apparently the price has gone up a lot. My LCS just got one.

@mar, yes I have one and would definitely recommend as an adjunct to specific gravity testing. Here is a link to an old thread where I describe using it:

http://goccf.com/t/397629

Added: and here is a link to an older CCF thread talking about them:

http://goccf.com/t/281120

I got one a couple of months ago since we got into bullion more. They are expensive. Found mine slightly used for $1000 cad.

I purchased one recently from the USA. I'm in Australia and got it slightly cheaper than buying locally. Unfortunately the first unit was faulty and its internal battery didn't work, but Sigma sent me another unit that worked fine.

I am happy with my Sigma and as I regularly attend estate auctions, it's great for testing coins. I have already found a fake ~$400 coin that I would have otherwise contemplated purchasing.

It is very sensitive to even slight alloy changes. For example, I have some certainly genuine sterling silver UK crowns from the late 19th century that test non genuine on the Sigma. Just a little contamination with metals other than copper, or perhaps a little bit too much or too little silver, and the coin tests as suspicious.

It does have a raw measurement mode too, so if you know the expected value for coins of a particular age you can test that way. And of course, a counterfeiter could make a fake using the right alloy too.

Speaking of which, does anyone know of a database of Sigma measurement mode values? I have three Maria Theressa 1780 83.3% silver coins. These were restruck and often faked.

Two measure 1.88, the other is 2.09. They all weigh the same and are of the right thickness.

It would be really great if someone's compiling a list of known good values of coins.

There are times where it's not possible to test the weight and dimensions of a coin. I often encounter this at estate auctions, where people have slabbed coins or put them into flips I can't rip open because the staff would get mad.

An XRF is the gold standard in testing, but even that is not fool proof.

I use my Sigma as an additional tool to help me find dodgy coins. Whether it's worth spending so much money on one is up to the individual. One good thing however is they hold their value, and second hand units are very rare. You're likely to get back most of the unit's purchase price in a few years if you choose to sell.

@Spence, depends on the model and the probe. Sigma publishes how deep their device can test metal. Burying a tungsten bar more than a few mm below the surface is probably going to fool the Sigma, but if you're buying gold bars that large then I would be buying from a trusted source anyway.

@Dorado, I know your post wasn't aimed at me, but I thought I'd respond as you touched on an important topic.

First of all, that page with the fake coins and resistivity readings is a helpful resource. Do you know of any pages like it for genuine coins?

While the Sigma is a very handy tool, it is possible to fool it by playing around with the plating and alloy to make the fake bullion. Remember that counterfeiters can buy the Sigma too, and experiment with it to make a better fake product.

But to make a coin/bar with the right weight, size, and resistivity would require considerable skill and may be beyond most counterfeiter's abilities.

Another problem area with the Sigma is false negatives. I have 2 Australian $200 22K 1981 gold coins, but they both test outside the brackets on the 91.6% setting. My coins are genuine (testing by look, weight and size), so it's possible the maker didn't solely use copper when alloying to make 22K.

I have a Sigma and have previously praised the device, with some caveats, but yesterday I came across an interesting example where the device gave erroneous readings.

I purchased three Napoleon 40 Francs gold coins from a reputable auction house that guaranteed authenticity. 1808, 1810, and 1812. After receiving my coins I tested them all using the wands and the 22K gold setting. 1808 and 1810 tested perfect, but the 1812 coin was off to the far right. Oh no, did I get a fake coin? It looked real...

The measurement mode gave 9.08 and 9.7 for the genuine coins, but 14.8 for the suspect coin. Thinking I might have been ripped off, I took the coins to my trusted bullion dealer that does XRF testing for free (don't know if I can mention them here however...)

All the coins tested between 21.3 and 21.5K gold, with copper and impurities of silver and lead. Tested on both sides of the coins. I didn't press the staff member for the exact composition of the 1812 coin, but it appears the impurities completely threw the Sigma off.

So, the Sigma is a wonderful tool, but use it with caution.