Featured Counterfeit Gold Eagles w/pics of core taken out.

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Can someone recommend a good digital scale that can accurately weigh (gold) coins including those in slabs so that I can weight them correctly as an added check against counterfeits ?

I'd like to buy from Amazon.

 

I don't see how one could accurately weigh them in the slab. Slabs are held to no standard weight even when they are the same design; and they change them up quite often.

 

Could the weight of current slabs change that much from slab-to-slab ? I would doubt it. They all are made from the same materials and have the same size.

 

This is correct. The new PCGS slabs, for example, are significantly lighter than the older ones, even though they seem bulkier. Even if you had average weights of every slab generation, there's probably enough variation to render a coin weight inaccurate.

 

Every slab type has its own specific weight, no ?

I'm not talking about assigning an 'average weight' to dozens of slabs and then weighing them in total. Each individual coin and slab will be measured solo.

 

No. One has no specific weight to assign any slab.

However, what you said "Each individual coin and slab will be measured solo." would work fine.......but then the coin is not in the slab anymore and you are right back where you started.

 

David, what I am saying is that each slab type should weigh pretty much the same. They are mass-produced to the same dimensions and specifications; how much can their weight vary ?

So....if I am weighing coins in PCGS Version 5.0 slab or the slab used in 2014...or NGC's slab from 2010....then once I know what each of those slabs weighed EMPTY....I should be able to then tell what the combined weight would be for various coins, knowing what the coins weigh solo.

So if I have a Morgan in a PCGS Version 5.0 and know what a Morgan weighs, I should be able to tell what it weighs in the slab pretty accurately. Ditto for a Saint Double Eagle or other bullion coins.

 

Within the tollerance of your scale and of the Morgan's themselves... yes.

Say your scale reads to 0.01g with an accuracy of 5%. This typically means that 95% of the time, the weight shown will be within 5% of the true weight (95% CI - confidence interval).

For a Morgan $ - uncirculated, as it came from the mint (zero wear), is 26.730 grams with a tolerance of (+/-)0.097 grams. Or 26.633 to 26.827. Assuming the coin was within tollerance when issued (a decent chance, they did check samples).

And for ease of calculation the Morgan in the slab weight 100g.

So the slab + coin actually weighs between 95.00 and 105.00 grams.

Subtracting the coin weight gives you the slab weight.

95.00 - 26.827 = 68.173 but you lose the digit (limiting accuracy is the scale), so 68.17
105 - 26.633 = 78.367 or 78.37.

So your slab weight is 73.27 +/- 5.10g (for reference, a US Nickel weights 5g)

In order to improve that accuracy, you need to measure 100s of examples of the same coin, same wear state and same slab+gasket, etc. The formulas to use are left as an exercise for a reader who has taken statistics more recently than I...

Can it be done? Sure.

 

As far as I know no one has ever weighed a large number of cracked out empty slabs of each (or any specfic) generation to develop a weight tolerance range. And I would expect there to be a range of weights for any particular generation. (Not to mention a given weight and range for each denomination.)

And since the tolerances of the coin and the slab would be additive the use of a weight in the slab would still be questionable. For example a fake Morgan that is .1 grams below tolerance in a slab that is .1 grams heavy would show a total weight within tolerance.

 

A very good chance, they weighed every planchet.

 

Thanks Burton...yeah, it's just an additional check for me for coins.

Would I be doing this if a digital scale cost what they did 15 years ago ? No, I probably wouldn't invest a few hundred dollars in a quality scale to do this.

But for $25 or so, if I can catch a gross weight error, it's worth it. Someone getting the weight pretty accurately on a counterfeit to within 99% of actual weight, I probably will not catch.

 

Burton, I think your math is off:

So far, so good.....

I'm not sure about this....if the accuracy is within .01 grams, it's going to be 5% accurate +/- that 0.01, NOT the total weight of the object. It's not going to "guess" the weight of the coin+slab as between 95 - 105 grams. Not if it's accurate to within .01 grams with 5% inaccuracy.

It's going to weigh it probably as 99.8 - 100.2 (I'm approximating 2 Standard Deviations).

It won't be off 5 grams either way.

 

Your arithmetic is correct, but I think assuming only 5% accuracy for even these cheap scales is pretty harsh. I would expect absolute accuracy as shipped to be closer to 1% in the general case, and the scales can be user-calibrated to improve that greatly.

Repeatability is the more important issue. If I weigh the same coin many times, how much does the weight vary? In my experience, even the cheap scales do a pretty good job at this. This means that if you have a known good coin to compare to, you can establish with very high confidence whether an unknown coin is likely to be within tolerance.

If I get some time, I'll run some experiments on my scale and post the results over on the scales thread where we've been discussing this.

 

What is this "source" ?
Can they explain why they think it is counterfeit ?
Can you explain why you think it is counterfeit ?
Based on that picture, I am skeptical of the accuracy of the source.

 

http://www.awscales.com/support/terminology

For giggles, let's redo the same calcs at 1%AR...

Morgan $ 26.730 grams with a tolerance of (+/-)0.097 grams. Or 26.633 to 26.827. (same)

So the slab + coin actually weighs between 99.00 and 101.00 grams.

Subtracting the coin weight gives you the slab weight, 99.00 - 26.827 = 72.173 but you lose the digit (limiting accuracy is the scale), so 72.17

101 - 26.633 = 74.367 or 74.37.

So your slab weight is 73.27 +/- 1.10g

So it's just barely accurate enough to differentiate between a silver and cupro-nickel Ike $ (1.91 grams, the cupro-nickel version weighs 22.68 grams, the silver Ike dollar weighs 24.59 grams or 1.91g difference).

 

But the Silver and clad Ikes also have tolerances +/- .907 grams for the clad and.984 grams for the silver. It is almost impossibly to conclusively tell them apart by weight alone even without the slab (The clad can weigh as much as 23.58 grams and the silver as low as 23.6 grams) Put them into a slab that has a weight variance of as much as 1.1 grams and you can forget it. Your clad coin in a slab could weigh as low as 93.94 grams to as much as 97.95 grams. The silver coin could weigh as low as 95.77 grams to as much as 99.94 grams. So if your actual measured weight is between 95.77 grams and 97.96 grams it could be either one.

 

OK, I got my ET Matrix Digital Scale today....very nice product. It comes with a 100 gram calibration weight.

I weighted 2 of my coins in their slabs. I'll try and track down the weight of the empty slabs and look up the coins weights later (going out for a few hours):

(1) 2013 Reverse Proof Buffalo Gold in NGC Black Slab: Weighed it 2 times.....70.82 grams and 70.81 grams.

(2) 1884 Morgan Silver Dollar in Version 4.0 OGH PCGS Holder: Weight was 54.71 and 54.70 grams.

I'll weight them again tonight but so far a difference of 0.01 or 0.02 (it moved from there) isn't bad.

 

But if you get 94.00 grams and 99.00 grams them you could have a problem coin
There is no hurt in weighing the slab coin

 

If you get 94 grams you have a clad coin or an underweight silver one. If you have a 99 gram weight you have a silver one or an overweight clad. Now from just the weights, what do you actually have? Weighing the coin in the slab doesn't hurt, but it may not tell you anything either.

One reason this discussion started was for the possibility of detecting counterfeits by weight weighing the coins in slabs. So lets imagine two Morgan dollars a genuine and a fake that is .5 grams light (tolerance on a Morgan is .09 grams so our fake is well out of tolerance.)

The fake in a slab could weigh between 98.4 to 100.6 grams. Our genuine 98.8 to 101.2 grams. So our well out of tolerance fake could be taken as a genuine if our observed weight is between 98.8 and 100.6 grams. Weighing it in the slab will only identify it as a fake if it weighs less than 98.8 grams. (And even then it MIGHT be a slightly out of tolerance genuine coin.) Since most every weighed slabbed silver dollar will weigh in that range, weight of a coin in the slab will seldom be able to tell you if a coin is real or fake.