Weight tolerance of coins for authenticity

I'm wondering what the weight tolerance is for coins to determine its authenticity with respect to the issued weight of coins. For example, if a Peace dollar is supposed to weigh 26.73 grams, is 26.6 grams reasonable?

Is there a rule of thumb like +/- 0.1 grams, or a percent deviation tolerance? I would assume that circulated coins over time would exhibit similar weight loss due to wear, regardless of denomination. I'm sure there could be weight gain, but I am assuming that all dirt and other light debris are cleaned off the coin.

Thanks in advance.

 

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Depends on your scale, but it sounds acceptable to me, and get a scale that will handle .01 gram.

 

Thanks.

Does anyone know what +/- tolerance is unacceptable across different coin sizes?

 

I trade junk 90% silver, and buy/sell it by weight. 2-3% weight loss is typical for well-circulated junk. I bought $100 face value of beat Mercuries recently. When minted, there things weighed 2500 grams. These slickers tipped my scale at 2445g...a 2.2% weight loss.

if i were to put 100 AU Franklin halves on my scale, i would expect the weight to come in within 3-4 grams of 1250.

 

Could be due to silver and gold being used in older coins. Germany's 1873 coinage law specified a tolerance of 0.2 to 0.5 percent for the gold and silver coins. Nobody actually cared about the weight of copper pieces then.

Today's euro coins may have a 3.0 percent tolerance per piece, but a lot/bag of 100 coins for example should not have more than 1.0 percent. The recommendation of the European Commission says "between -2% and +1%", I think.

Christian

 

Coin World Almanac

Lists the weight for every US coin in grains and grams plus the tolerance range in both units. Also lists diameter, composition and Specific Gravity.

Peace dollar is 26.73 grams (412.5 grains) with a tolerance of +/- .097 grams (1.5 grains) That's .36%

If it does you have real problems because 1000 Franklin halves should weight 12,500 grams

As Doug mentioned the percentage varies by denomination and composition. The Peace dollar tolerance as I mentioned is .36%, the franklin half is 2.1% a coppernickel five cent piece is 3.88%. Gold tended to be very strict. A double eagle was .095%. The tolerances also varied at different times. The Franklin half tolerance was 2.1% (+/- .259 grams), but the Walking Liberty half was .77% (.097 grams).

 

So he did, don't know why I saw 1000.

 

Okay, so what role does Specific Gravity play in numismatics? I believe it has to do with authentication?

I see scale/specific gravity kit for sale here:
http://www.valleycoin.com/product_info.php?products_id=33034

 

I once had a local dealer tell me he thought my gold coin was fake because the weight was off something like .05 grams. I asked him what his nickel should weigh, then had him weigh it. It was off even more. So I asked him if he was selling fake nickels. He didn't like that, but some of the other customers chuckled...

 

Common use , Specific gravity of a metal or other substane, indicates its mass/vol ( density) relative to pure water @ 4 deg.C.

You need a balance which allows you to measure the mass of the object( coin) in air and in water.

If you have a balance, this setup works fine. The accuracy of your specific gravity reading will be based in the balance's ability ( resolution ) usually marked or given. (0.1gram, poor) , ( 0.1 milligram, excellent resolution)

http://www.mineralab.com/Scale.htm

 

Nice link.

So, this is what I'd like to know: There is a "bronze" (so called) variety of a certain coin that has an 88% Copper, 12% Zinc composition, and coin made the same year with a (so-called "brass") 65% Copper, 35% Zinc composition (the mint changed metal ratios due to increases in copper prices that year). Could specific gravity tell me the difference between the two varieties?

What would a person need to know about attempting to do this?

 

The 88% copper/12% zinc mix should have a sp.gr. close to 8.715 and the 65% copper/35% zinc mix should be about 8.301, and should be determinable, if the mint tolerances were the same and relatively a small% , and the scale had good resolution.

If the size of the coins ( volume by water displacement) was the same, the difference should show by accurate weighing (no sp gr. test needed), unless a very small coin and the mint tolerances statistically made it undetermined.

Because of a different sp. gr. , the 2 varieties could not be both the same design, volume and weight. If same volume/design, I would just determine by weighing accurately. If different volume/design, I would use the sp.gr. method.

 

Both are same design, same volume, just different metal ratio.

Really? Just weighing them would do it? Both are listed at 4.06g

So, which one will weigh more? The one with the higher copper ratio?

 

Yes, copper is higher than zinc. But what are the tolerances as given by the mint, ( 4.06 +/- ?? grams )if they do give it. Often when this has happened ( different ratio is used ) the country may change the ratio on a sliding decrease, as they use up old reserves to prevent any hoarding, and can use different suppliers. I am assuming this is a Euro nation coinage as the formula seems to be what is called "Nordic Gold" brass.

 

I estimate that the latter coin would weigh 3.88 grams if that helps and the assumptions about volume is correct. But if the tolerances were +/-0.1 gram, the first could weigh 3.96 and a copy of the second variety 3.98 so they would theoretically be indistinguishable ( over lapping) although there should be some color difference.

 

It would only take a slight change in thickness (about 4%) of the 65/35 coin to give you the same weight for both coins. For example if the 88/12 coin was 1.5 mm thick the 65/35 coin would only have to be 1.57 mm thick to have the same weight (assuming the same diameter) A .07 mm increase in thickness would be hard to detect visually. Especially considering the edge thickness across a struck coin will vary depending on the strength of the strike.

 

Okay. So here are the stats that I have for both varieties, 88/12 and 65/35:

The coin is the 1970 10 Won coin [KM-6 and KM-6a]. South Korea (yeah, yeah, I know... my obsession again):

Diameter: 22.86mm
Width (thickness): 1.60mm
Weight: 4.06 grams (Krause 2012 World Coin Catalogsays BOTH are 4.0600) p.1345 of 39th Edition.

The weights are listed as the same(?) to the .01 of a gram (according to the information from the published Korean source that I have).

No +/- tolerances noted. These coins were made in the late 1960s and early 70s.

+/- tolerances of a hundredth of a gram were not noted on Korean Mint-made coins until 1970 and the introduction of the 100 Won coin, and all of their subsequent coins.

The Korean Mint changed metal ratio after spikes in copper prices due to copper mine strikes in the USA in 1967-68.

When the TPGs grade these, I've "heard" that they only dope-eye the color of these 1970 10 Won coins to type up the BRONZE or BRASS variety on the slab tags. I also heard that they do NOT use specific gravity measurements.

I would like to know if I could use SG measurements to distinguish the varieties. Is this possible?