Is acid testing safe? What precautions should I take?

Shhh!

 

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Silver-plated copper and nickel are most commonly used. The percentage varies slightly but generally is about 15-25% off. You are correct, this method only works for smaller bars and rounds. For larger sizes, such as a 50, 100, or 1000 ounce bar, we use an XRF metal analyzer. You can use a drill but it can damage the resale value.

@Gam3rBlake you are correct also. I failed to mention you should use a magnet first. This will determine if there is any iron (most commonly used to allow to the correct weight) in the piece. This will cover just about every fake that I have encountered (although we mostly see low grade fakes here), but an XRF metal analyzer is the only way to know for sure.

 

I really, really want an XRF analyzer. But it would just be a hobby tool, and I wasn't raised to spend five figures on hobby tools.

But if they start coming down into the low four figures, I just might not be able to resist. Point at something and get a quantitative elemental analysis? How cool is that?

 

I have to admit they are pretty cool. We just got a new one since the heater on our old one started to go bad. I think it was about $25,000. Seems crazy but it pays off in man-hours and not buying fake stuff. In addition, it allows us to purchase items other shops can't, like palladium contacts from old grand pianos.

 

You can get a Sigma Metalytics machine that does basic metals testing for $800.

It can tell you if something is :999 silver or gold or .9999 or 90% like old silver coins and basically you just set it for what the coin/bullion is supposed to be and it will tell you if it’s real or not.

 

The Australian YouTube channel & bullion dealer BullionNow also has one of those top end XRF machines with an attachment that looks like a gun for portable testing.

 

Is Tungsten magnetic though? Tungsten scares me because it’s slightly heavier than gold so a counterfeiter could use Tungsten and a lighter non magnetic metal and then a gold wash to achieve the same size and weight as an authentic gold coin regardless of what type of coin it is.

An all tungsten coin with a gold wash would be a bit too heavy but replace some of the tungsten with a lighter metal that’s not metallic and counterfeiters can make coins that could fool anyone but experts & people with access to an XRF machine.

 

Tungsten is ferromagnetic meaning it is slightly attracted to a magnet like silver. If you are looking at a "gold" coin and it is at all attracted to a magnet, that's not a good sign. It cannot be used for accurate silver counterfeits because it is more dense than silver, meaning the weight will be off.

 

Not the same thing at all. Sigma machines just check a couple of electromagnetic properties. They won't tell you the composition of an item; they'll just tell you whether or not it gives a signal matching the composition you expect. And they can definitely give false positives and false negatives.

An XRF analyzer gives you an actual analysis of the elements and percentages in your sample. You don't have to tell it what to look for.

 

The XRF and Sigma machine use different principles for measuring samples. Both have positive and negative attributes.

Yeah, I would love to have one too. But a benchtop SEM would be a lot more fun, and if it had EDS capabilities, you could skip the XRF unit. Looked at a bench top Hitachi for a business application about 15 years and thought it would look nice in the garage, but didn't have a spare $75k sitting around

Also @Gam3rBlake didn't see anybody mention this, but some more basic Chem lab 101. Don't set the dropper on the counter, put the dropper back in the bottle as soon as you're done. There is acid on the outside of the dropper that can damage the counter or you could inadvertently touch the residue.

 

Tungsten isn't ferromagnetic, it's paramagnetic. I don't have direct experience, but as I understand it, the effect is way too weak to detect with an ordinary bullion-checking magnet. Have you actually been able to lift tungsten with a magnet? I know there's tungsten jewelry, and if you come across any, it would be worth trying.

The tungsten-filled fake gold I've seen (pictures, not in person) has a thick outer layer of gold around a tungsten core. You can strike up a coin from one of those blanks, but tungsten itself is too hard to strike -- that's why it would be hard to make a tungsten coin and then gold-plate it.

This technique is bad news for XRF, too, because the X-rays from the gun can't penetrate the gold deeply enough to reach the tungsten and produce a signal. As far as I know, the best ways to check for tungsten-filled gold (especially bars) are electrical or acoustic (ultrasound). I'm guessing that one of those Sigma machines might reject a gold coin with a tungsten core, but again, no direct experience.

 

I think the Sigma Machine (resistivity test) would do a good job on gold with a Tungsten core

As @-jeffB mentioned, XRF is primarily a surface measurement technique. The X-Rays will penetrate slightly below the surface up to a few hundred microns (dependent on the metal, xray energy, surface contours and other stuff), but it won't tell you what is in the center of a coin

 

Thanks for the info!

Just one more question:

What will happen if I apply this 22K testing solution to an authentic American Gold Eagle?

An AGE is 91.67% gold which just barely falls into the 22K range.

I know Gold is completely inert and unreactive and that’s why it’s called a “noble metal” but does this mean the 22K acid will not do any damage to it and will leave it in pristine condition while destroying anything that’s not gold or is less than 22 karat gold?

Or will it leave a mark on 22k & 24K Gold as well?

If so what about lesser acids like 10K testing acid?

Thanks again!

 

I haven't tried it, and I won't. But AGEs have copper alloyed in with the gold, and acids certainly do attack copper.

As I understand it, you're supposed to drag the test item across the stone, then apply acid to the streak. If the acid attacks copper in the alloy, you might not see a visible effect on the streak, but you still might see a visible effect on the coin's surface.

 

One of my favorite chemicals Gold (III) chloride , so it is not inert.

Read this before doing anything.

https://geology.com/minerals/streak-test.shtml

 

I thought that’s why there were different types of gold acid testing solution?

Like if you applied 22K acid to 14K gold there should be damage due to it not being enough gold.

But an AGE is 22K gold so the gold content should be high enough to resist damage regardless of the copper no?

 

No.

It's not a binary thing, where the alloy is either attacked or untouched. I don't know that 14K test acid would damage 22K gold, but I wouldn't try it on an otherwise undamaged coin.

 

Ah ok I gotcha.

Yeah I would never ever do it to an uncirculated coin even if it’s just an American Gold Eagle with no numismatic value.

I was just asking as a hypothetical question to know what would happen without having to do it.

 

HI. Keep this in mind. ANY acid that will react with copper will eventually environmentally damage a coin that has copper in its composition. Whether it is from a gold and silver testing kit or even PVC poly vinyl Chloride which breaks down into the chloride/chlorine acid. In one of my previous posts, I mention an ANA graded coin from the 1970's that they graded and put into a PVC heat sealed flip. When I got to it a couple years ago (after 40 years being in my safe deposit box), the PVC oils had leached onto the Proof 1937 Australian Crown. Even after many baths in Acetone, The PVC oil had microscopically attacked the copper in the sterling silver crown. Ask questions here first before you do anything. The experts on Coin Talk will steer you in the right direction. Enjoy your coin collecting.

 

What about a .9999 Gold Buffalo then?

No copper whatsoever except potentially 0.0001% which is like the size of a microbe.