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I weighed a stack of 17 Libertads of varying years and found some surprising variation. Anyone else have a stack and a 0.01 gram scale to see what they get?

Reason for my concern is... do I have some counterfeits in these?

I've previously noted some measured data on variation in BU US circulating 90%, which was never intended to be a precise container for silver.

But my previous measurements in .999 bullion coin (Maples, ASEs, etc) have shown very consistent weights to the 3rd decimal place, varying only in the 4th digit.

However, I weighed these 17 LIbertads and found three groups: one I will call "nominal" at 31.10 to 31.22 grams (population of 10), 6 light (30.84 to 30.99), and 1 heavy (31.32)

Keep in mind that true nominal is a minimum value of 31.134 (1 toz/.999)

The data is below. You can see the clear breaks in groups. The overall average is 31.08 (not bad, but slightly low). But the first group of 6 averages 30.93. the second group of 10 averages 31.16 (which is what I would expect), and the last group of 1 averages 31.32. There's a nearly 0.4 gram difference between the light and heavy groups.

30.84
30.9
30.92
30.96
30.99
30.99

31.10
31.11
31.12
31.14
-------< they should typically weigh about here
31.15
31.15
31.17
31.19
31.21
31.22

31.32

Blah, blah, blah...

Too many cervezas in the QA dept?

Engineer wrote:Too many cervezas in the QA dept?

Dude, where's the curiousity?!

Could it have anything to do with the mintage year? This wiki http://en.wikipedia.org/wiki/Bullion_coin shows '91 to present as .999 and pre '91 as .900 i guess the variance you found probably isn't enough for purity to be the answer, but i thought i'd throw it out there.

EDIT: Ooooops! i was reading the gold section. The silvers have always been the same purity. Could it be your scale? Have you calibrated it recently?

dannan14 wrote:Could it have anything to do with the mintage year? This wiki http://en.wikipedia.org/wiki/Bullion_coin shows '91 to present as .999 and pre '91 as .900 i guess the variance you found probably isn't enough for purity to be the answer, but i thought i'd throw it out there.

EDIT: Ooooops! i was reading the gold section. The silvers have always been the same purity. Could it be your scale? Have you calibrated it recently?

miscalibration would not account for the bell curved results that he has found. It would be more likely to show end-liars (sp intentional ) as in the entire group being low (beyond expected variances) or high... not the even spread demonstrated.

Good thoughts, but...

Scale is calibrated with precision weights.

The Libertad is the later subcategory of the "onza", which are all 1 toz coins, but were first done in sterling from 1978-80. In 1982 the Libertad design came out as a .999 bullion coin. The older coins weighed far more, 33.625 grams nominal and are larger diameter at 42 mm vs 36 mm for the Libertad. They can't be easily mistaken.

As far as it being a issue of year within the series, there is no correlation of year and weight. The same years share both light and nominal weights (and heavy, for the one example).

In the absence of an XRF scanner, you could test them with an induction slide...but that may not be an option if you're trying to keep them in BU condition. Putting them in a 2 mil PE baggie might be an acceptable way to protect the surface from scratches if you do decide to send them down a slide.

If I had to guess, I'd say the mint was just a little sloppy on planchet thickness. With so much silver production and so many different types of silver coinage in Mexico, it's possible that they simply didn't see the need to reject overweight feedstock.

You could also try measuring the fields with a micrometer. It would vary slightly depending on the strike, but with enough data you should be able to correlate thickness vs mass vs strike.

That's what I'm thinking - hoping. On average - given enough of them, they are very close to nominal. But the individual quality control is more like what we see in US 90%, rather than the much tighter control we seem to see with ASEs or Maples.

68Camaro wrote:That's what I'm thinking - hoping. On average - given enough of them, they are very close to nominal. But the individual quality control is more like what we see in US 90%, rather than the much tighter control we seem to see with ASEs or Maples.

consider the source

beauanderos wrote:

68Camaro wrote:That's what I'm thinking - hoping. On average - given enough of them, they are very close to nominal. But the individual quality control is more like what we see in US 90%, rather than the much tighter control we seem to see with ASEs or Maples.

consider the source

Well, for anyone here that might be from or have heritage from that country, this is not a personal slam at all, but... it did cross my mind that that is not the first country one thinks of when precision comes to mind. Switzerland, Germany, Japan, yes. Mexico? Not so much.

I post this to note the observed response of a random population, both for myself as well as others. The very variation is, itself, a signature. If I bought a roll of Libertads and they were all exactly 30.9x, or all exactly 31.2x - it would now send up a red flag to me. Hmmm, unless it was a mint roll that had all come from same planchet at same time, that might be TOO precise for these to be "normal" for Libertads.

Are you seeing any variations in the design of the coin? Most fakes are flawed in some way. I agree that lax quality control is the likely problem, but I would feel better about that conclusion if there was some external confirmation; like an article in Kitco.

i have a short stack of libertads myself. while they weigh different depending on year, mine are never under 31g