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<p>[QUOTE="-jeffB, post: 3738674, member: 27832"]Metal wears off the <i>surface</i> of a coin, but the coin's weight is determined by its <i>volume</i> (and density, of course). Increase a coin's diameter by X, and its surface area goes up by X <i>squared</i>, but its weight goes up by X <i>cubed</i>. Smaller coins have more surface area <i>proportional to their weight</i>, so they lose a greater <i>percentage of their weight</i> for a given amount of wear.</p><p><br /></p><p>To make this concrete: a really slick Barber dime might have lost as much as half a gram of metal, or 20% of its weight. A really slick Barber half, with around three times as much surface area, might have lost as much as a gram and a half of metal -- but that's only 12% of its weight.</p><p><br /></p><p>So, a $500 bag of those slick Barber dimes would weigh 10kg, instead of the nominal 12.5kg. A $500 bag of the slick halves would weigh 11kg.</p><p><br /></p><p>Now, you'll only see this degree of weight loss on <i>really</i> slick examples, the kind where even the date is worn away. But the same principle applies for less-worn coins; I've weighed quite a few Barber dimes (and even some Mercury) that were down by 10%, but hardly any Barber halves that were down more than 5-6% or so.</p><p><br /></p><p><a href="https://archive.org/details/annualreportofdi1902unit/page/18" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://archive.org/details/annualreportofdi1902unit/page/18" rel="nofollow">Here's a report from the Mint</a> (1902) on "uncurrent coinage" that they melted for reuse. It's got detailed breakdowns by denomination and year, but here's the top-level summary:</p><p><br /></p><p>[ATTACH=full]1002721[/ATTACH]</p><p><br /></p><p>The old coins they recycled had lost, on average:</p><p><br /></p><p>Halves -- 3.9%</p><p>Quarters -- 6.0%</p><p>Dimes -- 6.9%</p><p>20-cent pieces -- 2.2% (remember, these didn't circulate much)</p><p>Half dimes -- 13.7% (the table says 1.37%, but that appears to be a typo)</p><p>3-cent pieces -- these seem to have <i>gained</i> weight</p><p><br /></p><p>Here's a nice summary separated not only by denomination but by decade:</p><p><br /></p><p>[ATTACH=full]1002722[/ATTACH]</p><p><br /></p><p>The exact proportions vary, but in every case halves lost the lowest percentage weight, and dimes the highest.[/QUOTE]</p><p><br /></p>
[QUOTE="-jeffB, post: 3738674, member: 27832"]Metal wears off the [I]surface[/I] of a coin, but the coin's weight is determined by its [I]volume[/I] (and density, of course). Increase a coin's diameter by X, and its surface area goes up by X [I]squared[/I], but its weight goes up by X [I]cubed[/I]. Smaller coins have more surface area [I]proportional to their weight[/I], so they lose a greater [I]percentage of their weight[/I] for a given amount of wear. To make this concrete: a really slick Barber dime might have lost as much as half a gram of metal, or 20% of its weight. A really slick Barber half, with around three times as much surface area, might have lost as much as a gram and a half of metal -- but that's only 12% of its weight. So, a $500 bag of those slick Barber dimes would weigh 10kg, instead of the nominal 12.5kg. A $500 bag of the slick halves would weigh 11kg. Now, you'll only see this degree of weight loss on [I]really[/I] slick examples, the kind where even the date is worn away. But the same principle applies for less-worn coins; I've weighed quite a few Barber dimes (and even some Mercury) that were down by 10%, but hardly any Barber halves that were down more than 5-6% or so. [URL='https://archive.org/details/annualreportofdi1902unit/page/18']Here's a report from the Mint[/URL] (1902) on "uncurrent coinage" that they melted for reuse. It's got detailed breakdowns by denomination and year, but here's the top-level summary: [ATTACH=full]1002721[/ATTACH] The old coins they recycled had lost, on average: Halves -- 3.9% Quarters -- 6.0% Dimes -- 6.9% 20-cent pieces -- 2.2% (remember, these didn't circulate much) Half dimes -- 13.7% (the table says 1.37%, but that appears to be a typo) 3-cent pieces -- these seem to have [I]gained[/I] weight Here's a nice summary separated not only by denomination but by decade: [ATTACH=full]1002722[/ATTACH] The exact proportions vary, but in every case halves lost the lowest percentage weight, and dimes the highest.[/QUOTE]
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