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 Replies: 8 / Views: 3,444 |
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Pillar of the Community
United States
3276 Posts |
So my question when weighing coins is how much can the weight vary from the actual weight? I know some wear will mean it will weigh less. but if you take a Peace dollar for instance which weighs 26.73 grams, how much approx would a fake weigh? would it be close or would it be several grams off? I just bought 10 Peace dollars and they weigh between 26.63 and 26.74 grams, so I assume they are all legit. generally, when weighing coins what is acceptable? like if you weigh a silver quarter, how far can the weight be off and still be authentic? |
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Bedrock of the Community
United States
10982 Posts |
This tends to vary by series but if a coin is 10% underweight, it better look like a slick or have a big hole in it! For coins in VF/Better condition, 1% weight loss maximum is a good rule of thumb. VG/Better 2% or so. When the condition falls under G04 weight loss can get dramatic. I've seen slick SLQ that weighed 5.5 grams. That's 12% underweight! Your Peace dollars sound fine. Besides weight the biggest thing is handling coins and knowing what genuine pieces look like. I use to buy a lot of raw gold pieces and if the size, weight and look was good, that satisfies for common dates. |
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Pillar of the Community
 United States
3276 Posts |
thanks for the input BH. I like the 1% max rule of thumb, well excluding very worn coins.
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Bedrock of the Community
Australia
21786 Posts |
The measurement of weight is one of a number of tools for identifying a forgery.
If a suspect coin is say, more than 10% underweight, there is a strong reason to investigate further a coin that is already suspect.
However, good forgeries of correct weight do exist. For instance, it is possible to make an alloy of copper and lead that has the same density as silver which is 10.5 g/cc, or to use tungsten instead gold (then gold plated). Both tungsten and gold have a density of 19.2 g/cc.
Experienced eyes, assisted by good magnification, then have to be relied on to a greater extent. An experienced pair of eyes can identify faults such as style, texture of the surface, and flow patterns of metal as a result of a strike or cast.
Electrotypes can be picked by a join around the edge of the coin.
Sometimes, there is a tiny difference in the sharpness of the detail. This is the method that products of dies that are cut from an electronic data base model. Such dies are manufactured by laser optic profiling and spark erosion die cutting.
Such copies can be 'spot on' for weight, if the right alloy mixture or core metal is used.
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Pillar of the Community
United States
3546 Posts |
Having the weight, thickness, and diameter of a particular coin are fine in 90 % of the cases.
But if you want to be 99.9% sure of the authenticity of a very expensive coin I would suggest having the S.G.(specific gravity) measured by a professional.
All of the other methods for determining a coin's composition seem to be cost prohibitive to engage for the individual coin collector unless something new has popped up in the last six (6) months.
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Bedrock of the Community
United States
20753 Posts |
By weight is far from any real test today. China has long since been making their forgeries with the same Silver percetage as our coins. They do that since they well know collectors think they'll catch a fake that way. And just in case your considering only buying the slabbed once, remember China is now also making those too. Almost any coin made in China today is being made for collector purposes, not spending, so they use just as high grade materials as our original coins. Weight, thickness, diameter, etc. have little meaning if the fake is made with all the same materials.
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Pillar of the Community
United States
1064 Posts |
For mdpmedia; if you went to the trouble to get the S.G. for a coin, is there a way to tell what it SHOULD be, so you'd have a value to verify against? Would you just be asking the scientist what they think is correct?
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Bedrock of the Community
Australia
21786 Posts |
If an owner of a slabbed coin is unwilling to break the slab open, the slab can hide a fake coin therein. If there is any suspicion that the slab is fake, there must be the same level of suspicion that the coin inside is fake also.
Where a fake weighs the same as a genuine coin, but it's composition is different, the coin should ring differently.
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Pillar of the Community
United States
3546 Posts |
JackB, I will only say that I agree what this gentleman says in the following article regarding reliability of S.G: http://www.numismedia.com/101/index5.shtmlFor your info. here are the S.G. figures I personally have been using for the following metals: Silver: 10.49 Sterling Silver: 10.36 90% Coin Silver: 10.31 Remember, however, that the SG for a 90% silver dime will be the same as the SG of a 90% silver dollar; size is irrelevant for SG testing assuming the samples being tested contain the same %s of metal types. But the SG of a 40% silver Kennedy half, for example, will be less than 10.31 for obvious reasons. Incidentally, I personally feel that if no ‘economical' test currently exists that produces a 100% reliable verification of a coin's metallic composition, then virtually all collectors are in the same boat in terms of the exposure to risky coins. Even if one wants to invest around $ 100k for a piece of xray equipment to ascertain the exact composition of a coin it seems to be an exercise in futility especially since the Chinese are now using the same metals and associated percentages as the US Mint. In summary my suggestion is to: 1) initially weigh and measure the diameter and thickness then 2) inspect the surface for cast irregularities (seam etc.) per the following thread that I participated in several months ago: https://goccf.com/t/72134&SearchTerms=cast3) run a S.G. test yourself. 4) do the ring (tone) test as Sel previously suggested This should keep you out of any major trouble unless the counterfeiter has gone to extreme measures for some high dollar coin, which then should be sent off to PCGS for re-certification etc. fyi, mdpmedia |
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Replies: 8 / Views: 3,444 |
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Posted 04/30/2011 03:11 am
