Numismatic and History Discussions > Coin Photography, Conservation and Storage

Cataloging Estimated Dimensions of Slabbed Coins

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Ken W2:

Some NGC slabbed coins provide a weight, but many provide no weight or diameter. Diameter can be fairly accurately measured with a good caliper through the slab. Weight presents a harder problem. It occurs to me though that the holders may be fairly uniform in weight, and thus the weight of the coin can be estimated.  Sure there will be some variation, in part because the white insert actually holding the coin will vary based on the diameter of the coin. As a quick test, I weighed 3 NGC slabbed coins and after subtracting the stated weight of the coin the slabs all weighed within .07 grams of each other, and all 3 were nominally 40 grams. If, with a larger sample size, we could determine an NGC slab weighs X grams on average (or NGC provided the speced weight) we could derive an estimated weight to include in attributions and cataloging. So long it was stated to be an estimate, such estimate would not be deceptive and would have the value of confirming the coin is in the appropriate weight range for the issue. 
I’d welcome your opinions about the value of so estimating weights and any info you have about the standard weight of NGC slabs.

Jay GT4:
I don't remember but isn't the weight on the NGC lookup online?

Ken W2:

Unless I don’t know where to look, NGC look up only shows the slab and thus you only get the weight if weighing was included in the service selected.  I did a search online and found a thread in which others asserted the empty NGC slab weighs just under 40 grams.  That’s easy enough to confirm by weighing slabbed coins on which the weights are stated and doing the math.  But there will be some variation.  I guess what I’m really asking is whether there is any value in the attribution/cataloging process of so estimating. The only benefits I can see are confirming to coin is not out of the right weight range and having consistency in the items of info included in your attributions. 

Virgil H:
I only have two coins that were slabbed and I removed them from the cases as soon as I got them. I never thought to weigh the slabs. And the coins I had were not weighed by NCG that I know of, I weighed them myself.

Anyway, there are a couple ways to look at this. One is the weights of the cases plus the various sized holders and how accurate you can be with those. If those are known, one could get a reasonable weight for the coin. Your numbers that you have come up with so far seem reasonable and would benefit from a larger sample size.

Here is where I am going with this. The biggest question is what level of tolerance are you going for? How accurate do you need to be and at what point would being off make a difference. Many ancient coins have what I consider a large variance in weight. More than I expected when I first started collecting. So, I think that for many coins, a method of weighing the entire slab and subtracting what the estimated slab weight minus coin would be acceptable to many (most?) people.

It really depends on how accurate you want or need to be. I wouldn't do this if I were selling a coin and describing a specific weight, mainly because I am strict about tolerances for things like this. I would want to weigh the coin by itself. That said, no one calibrates scales any longer and, as an old Army calibrator who calibrated scales in commissaries, orderly rooms where people were weighed for the fat boy program, hospitals, and nuclear/conventional weapons storage sites (where weighing projectiles is done regularly to determine deterioration of the weapon), I haven't trusted a scale in years. With a coin, maybe I would say approximate weight or something, plus I may be the only person in the world who cares. Yeah, I know they say digital scales are infallible. I don't believe that. No one calibrates voltmeters anymore, either.

And although it is not really true, the inaccuracy in things weighed in grams is going to appear much more than with something weighed in kilos.

I sure don't trust my cheap China made digital scales any more than the one that weighs the meat I buy (other than I am cynical enough to believe the grocery scale is always going to be wrong in the store's favor). But, that is what we have today. If you can get a good range of weights for slabs with various sized inserts, it is probably OK, although it introduces an additional element of error. And there will always be at least some error.


Ken W2:

I have 21 NGC slabbed RSCs, but only six have the weight reported by NGC.  When the reported weights are subtracted from the total weight of the slab, the six average 40.09 grams.  BUT, when I tried to use that average weight as a predictor of coin weight, by subtracting 40.09 from the actual total weight of each slab, the estimated weights were off from the actual/reported weight of the coin by a range of .12 to a whopping .47 grams. While that range is close enough to determine whether a denarius, antoninianus, and proablty a siliqua, are within weight range tolerances, that's not accurate enough for me to include a weight in my attribution, not even as an estimate.
Sure, there will be variation across different scales, but I suspect most of this variation lies in the differing weights of the white inserts which are sized/milled to fit the particular coin and some variation in the larger clear plastic part of the holder.  After all, a 1/2 gram variation in items nominally weighing 40 grams is only a 1.25% variation.  But, if that variation leads to predicted coin weights with variations of up to 1/2 gram, in items nominally weighing 3-4 grams, the variation becomes roughly 12-16%.  Again, that's too much variance for me to accept this method of estimating weight and reporting it in an attribution.

Thanks for the responses guys.  I'd welcome the opinions of others.   


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