How Not to Get Ripped Off, part 2

[dualstow]

The original thread with this title has some good info in it. Since the price of gold has been climbing and there's been news of tungsten in bars, I wanted to ask a couple of questions.

I do follow the suggestions in the other thread in that:
1. I use reputable dealers
2. I test coins with a Gold Coin Balance.

So, I'm not terribly worried.

Still,
Q1: For those of you who use calipers, do you have to buy those $155 Mitutoyo's, or will cheap (US$15) ones do the job?

Q2: I just noticed today that the dimensions for a krugerrand at onlygold dot com are not exactly the same as on Wikipedia.
Wiki says the thickness of a krug is 2.84 mm while OnlyGold says they are
2.75mm thick.

Again, I'm not alarmed. The coins pass my balance test so far, and I prefer to buy coins in the future, not ETFs or other funds. I'm just wondering if anyone has a better source for the dimensions.

[WildAboutHarry]

Cheap calipers are fine.  If there is a Harbor Freight tools near you, a good digital set can be had for well under $20.

Thickness of a coin is not particularly easy to measure.  Thickness where?  Rim or field?  Rim thickness can vary quite a bit, even on the same coin.  Most general coin references usually just list diameter and weight.

The weight relative to diameter is probably sufficient to screen most counterfeits.  I've seen one fake Mexican 50 peso gold coin, and it was way under weight (but it looked pretty good on casual inspection).  I've seen a few silver fakes, and these usually fail the weight or the magnet test.

[Reub]

What other fake coins have people seen?

[dualstow]

Thank you, WAH. I was wondering if it had to do with measuring at the rim or at the springbok. Looks like that could be the case.

@Reub: I've heard talk and seen a video claiming a fake Austrian Philharmonic was found, but I ignored it because I have yet to find a single article about it.

[AgAuMoney]

What other fake coins have people seen?

Either I've not seen any gold fakes or I've not noticed...

Lots of silver fakes.

Mostly silver dollars purportedly from the late 19th and early 20th century.  Some were obviously the wrong weight (some seemed like aluminum or zinc, others silver plated copper) and others seemed to be silver but the details were bad (some just wrong, most fuzzy like they were cast instead of stamped).

Several different silver "rounds" that claimed to be 1oz silver but were just silver plated copper with no attempt to match the weight.

One silver round that claimed to be 10oz but was not even close - it was silver plated copper.

edit:  I've not seen them in person, but my dealer tells me he has seen fake quarters and halves similar to the silver dollars I mentioned above, and he is hearing increasing reports of them from other dealers.

[craigr]

I have never talked to a dealer that has seen a fake gold bullion coin. A gold coin balance may be enough for private sellers, but buying from a reputable dealer is still my best advice.

[Greg]

The original thread with this title has some good info in it. Since the price of gold has been climbing and there's been news of tungsten in bars, I wanted to ask a couple of questions.

I do follow the suggestions in the other thread in that:
1. I use reputable dealers
2. I test coins with a Gold Coin Balance.

So, I'm not terribly worried.

Still,
Q1: For those of you who use calipers, do you have to buy those $155 Mitutoyo's, or will cheap (US$15) ones do the job?

Q2: I just noticed today that the dimensions for a krugerrand at onlygold dot com are not exactly the same as on Wikipedia.
Wiki says the thickness of a krug is 2.84 mm while OnlyGold says they are
2.75mm thick.

Again, I'm not alarmed. The coins pass my balance test so far, and I prefer to buy coins in the future, not ETFs or other funds. I'm just wondering if anyone has a better source for the dimensions.

Regarding Q1, I've noticed on my own coins using my calipers that there is a reasonable amount of difference within diameters/thicknesses. I'm wondering what the spec is for the tolerances of the coins themselves, i.e. 25.4mm +/- .5mm?

[AgAuMoney]

Regarding Q1, I've noticed on my own coins using my calipers that there is a reasonable amount of difference within diameters/thicknesses. I'm wondering what the spec is for the tolerances of the coins themselves, i.e. 25.4mm +/- .5mm?

I haven't been able to find much in the way of specs, and too often what I find is contradictory. 

I do think you aren't going to be able to measure well with typical calipers.  You need the ones that measure just a point instead of a blade on an area.  The blade is almost impossible to get between the rim and the raised areas and the field and...

[WildAboutHarry]

Has anyone ever measured the "gap" in the Fisch or the other detector (whose name escapes me at the moment)?  I suspect that gap is some reasonable fraction wider than the "average" thickness.  With that value, you could at least set the upper limit of thickness for measurement with calipers.

How about a magnet slide?

Sliding silver coins on a ramp of neodymium magnets can distinguish fake silver coins.  Silver is diamagnetic and generates a magnetic response to strong magnetic fields.

Gold is diamagnetic as well, but I've not tried any on the magnetic ramp.  It would be interesting to give one of the China tungsten fakes a ride on the ramp.

And yes, of course I made a ramp.

[craigr]

Has anyone ever measured the "gap" in the Fisch or the other detector (whose name escapes me at the moment)?  I suspect that gap is some reasonable fraction wider than the "average" thickness.  With that value, you could at least set the upper limit of thickness for measurement with calipers.

How about a magnet slide?

Sliding silver coins on a ramp of neodymium magnets can distinguish fake silver coins.  Silver is diamagnetic and generates a magnetic response to strong magnetic fields.

Gold is diamagnetic as well, but I've not tried any on the magnetic ramp.  It would be interesting to give one of the China tungsten fakes a ride on the ramp.

And yes, of course I made a ramp.

That's a very slick idea!

[dualstow]

Very interesting video. I've got a few neodymium magnets, but of course the old fakes and the new fakes behaved differently. Thus, I'd need the slide, otherwise the small magnet test would be as frustrating as Greg's experience with his calipers.

I wonder what Harry would think of all this. Post-HB, it looks like we have another good reason to not make silver a part of the pp. In the realm of coins, doesn't it seem like most of the fakes are silver and not gold?

I think China's next move is to flood the market with fake testing equipment that will recognize tungsten, thin and underweight coins as the real thing. 

[WildAboutHarry]

That's a very slick idea!

Nice pun!

Very interesting video. I've got a few neodymium magnets, but of course the old fakes and the new fakes behaved differently. Thus, I'd need the slide, otherwise the small magnet test would be as frustrating as Greg's experience with his calipers.

I wonder what Harry would think of all this. Post-HB, it looks like we have another good reason to not make silver a part of the pp. In the realm of coins, doesn't it seem like most of the fakes are silver and not gold?

You can get the same effect by sliding a very small neodymium magnet down the coin, but the ramp is easier and a must for dimes

I think the more-silver-fakes phenomenon may be one of sample size.  I've touched many, many more silver coins than gold.  And the silver fakes I've found were pretty obvious, with a bit of observation and magnets.  Further, except for very rare numismatic coins, the cost of being wrong about a silver half dollar is small compared to the cost of being wrong about a Krugerrand.

I would like to do a tungsten coin versus gold coin comparison, though, to see if the slide works. 

I think China's next move is to flood the market with fake testing equipment that will recognize tungsten, thin and underweight coins as the real thing.

[Coffee]

I walked into a local coin dealer and asked them about fake gold coins, and they basically told me that the fake coins are so easy to spot, they could tell just by holding it and looking at it, with the naked eye.

Might be a good place to unload some fake coins.  LOL.

[AgAuMoney]

Has anyone ever measured the "gap" in the Fisch or the other detector (whose name escapes me at the moment)?  I suspect that gap is some reasonable fraction wider than the "average" thickness.  With that value, you could at least set the upper limit of thickness for measurement with calipers.

I think the main value is the Fisch and the like is gross variance.  E.g. lead instead of gold.  You cannot even come close to the dimensions of a gold coin using lead but will be off significantly in either weight, diameter or thickness, or some combination.  It's easy to see that kind of difference with calipers.

With tungsten the density is so close I bet it would fool the Fisch.

How about a magnet slide?
And yes, of course I made a ramp.

They are way cool.  I should probably put together a 'permanent' ramp...

[WildAboutHarry]

They are way cool.  I should probably put together a 'permanent' ramp...

I made mine from a piece of 3/16" steel plate, 3" x 14" or so.  I used a bunch of 10mm x 10mm neodymium magnets (5 across and 27 high). 

No gluing, etc.  I will probably mount it in some sort of wooden stand eventually.

The magnets are very strong and, in a group, semi-dangerous around hard drives, fingers between metal and the magnets, etc.  But real silver (and perhaps gold) coins slide very slowly.

[BearBones]

I made mine from a piece of 3/16" steel plate, 3" x 14" or so.  I used a bunch of 10mm x 10mm neodymium magnets (5 across and 27 high). 

Any way to show a pic? Where did you get the magnets?
Thanks.

[WildAboutHarry]

How is this?



Not pretty, but effective.

The magnets are straight from China via Ebay.

It really needs a wooden cradle, but that is another project.

[craigr]

The magnets are straight from China....

Oh the irony!

Maybe this fake silver thing is a marketing plan to sell more Chinese magnets?

Thanks for the pics. Cool project!

[Lone Wolf]

Sliding silver coins on a ramp of neodymium magnets can distinguish fake silver coins.  Silver is diamagnetic and generates a magnetic response to strong magnetic fields.

Gold is diamagnetic as well, but I've not tried any on the magnetic ramp.  It would be interesting to give one of the China tungsten fakes a ride on the ramp.

And yes, of course I made a ramp.

Great stuff, WildAboutHarry!  My hat's off to you for making your own, too. 

Did you have a fake coin that you used to test your ramp?

[WildAboutHarry]

Did you have a fake coin that you used to test your ramp?

A few, unfortunately.

If I can figure out how to do a short video I will try to get something posted this weekend.

[Pointedstick]

That would be awesome. I can't wait to see a demo!

[Tortoise]

Nice job on the magnetic ramp, WildAboutHarry!

Who would have thought that detecting fake gold and silver coins could be such a rich technical sub-topic within this forum offering the opportunity to geek out with fun DIY projects?

So far on this forum, if my memory serves me correctly, we've discussed the following list of clever methods of detecting fake gold and silver coins:

• Size/weight (e.g., scale and calipers or Gold Coin Balance)
• Audio properties (e.g., ring test to measure audio spectrum using free Audacity software)
• Chemical properties (e.g., acid test -- only tests the outside surface of the coin, though)
• Thermal properties (e.g., hot plate + infrared thermometer)
• Electrical properties (e.g., measuring voltage/current across the coin)
• Magnetic properties (e.g., magnetic ramp)

The list keeps getting longer!

Although this would probably be overkill, maybe certain combinations of the above methods might provide even higher levels of confidence? For example, performing the electrical, magnetic, or audio tests at both hot and cold temperature. The physical properties of metals tend to vary in a known, predictable way as a function of temperature.

[WildAboutHarry]

Thanks Tortoise.

You are right, a lot of this is a bit of overkill, since the two silver fakes I have on hand fail the weight test, the ring test, and look suspicious to boot.  But it is cool to see real silver coins resist the pull of gravity.

Apparently there is no easy way to share video short of YouTube, but here is an .mp4 file showing the slide in action.  It should play with QuickTime.  The coins are two French 10 Franc pieces from 1930s, one real, one fake.  The ramp is set at about 70-80 degrees above horizontal.

Can you guess which one is the fake

[BearBones]

Apparently there is no easy way to share video short of YouTube, but here is an .mp4 file showing the slide in action.  It should play with QuickTime.

Gonna make one, even if it is overkill. Just too cool. Let us know if this works for gold.
Thanks for sharing.

[WildAboutHarry]

Gold and silver are both diamagnetic, although I think the property is stronger in silver.  Tungsten is paramagnetic, which (I think) means that it is magnetic in the presence of a strong magnetic field.

I'm not sure (it has been a while since I took physics/chemistry), but I think if you ran a hunk of tungsten on the magnet slide it would run slower (maybe even stop?) than a same-sized piece of gold.