What makes a worn coin so smooth?
Romankow
Posts: 146 ✭✭✭
This may sound like a silly question, but I can't get my head around it. What makes a worn down coin smooth? Is it the fact that all the people who have touched the coin have flaked off little bits of metal over the years? Or is it that the users have pressed the metal flat so that details of the coin are lost?
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Friction. Each time a coin is handled a minute amount of material may be lost due to friction, similar to what we see on old marble stairs where there is a depression or groove where folks have walked for years and years.
In honor of the memory of Cpl. Michael E. Thompson
option 1 mostly. slow wear. also don't forget older coins may have seen action in various types of machines, eg slots, vending,...
google "pocket piece coin"
here is a link from numismatic news http://www.numismaticnews.net/article/coin-clinic-coins-wear-in-owners-pockets
I have a pocket piece 1970-D Kennedy Half I'm carrying for someone that wants one worn down to poor condition (lowest grade possible) I received it at mid Almost Uncirculated and it has worn down to mid to high Extra Fine (a few steps down)
I also have a 1924 Peace dollar that was in the Good Grade (details - won't get a "real," straight grade due to a scratch on the reverse). Now it's down to AG and that was fast at about 2 years. "GOD" and "VST" were barely there and now it is just "OD" and "V" with a bit of the "S." This one I'm going to stop carrying soon because the area where the mint mark would be (it has none -> Philadelphia) is almost obliterated (a bit of a ray left)
I'll post pics of each in a few days when I get a chance.
Even the 14kt coins get smooth.
bad close ups from march 2014
Older coins were made of really soft metals (copper, silver and gold). These coins wore due to frictions as state above. They rubbed against each other in pockets, tills, machines, etc. Over time they just wear down to a slick.
bob
PS: some of today's coins will not show the degree of wear, that the older coins show in anyone's lifetime, due to the use of the hard metals used today.
Sliding in and out of these things creates friction and wear over time
Steve
Ok, it seems as if you're all saying that flaking off of metal is the reason for their wear. So, if that's true, then clad quarters (1965 upward) should flake off their cupronickel coating to show their inner copper core. But I've never seen a quarter in circulation that is worn down to its copper core. Is that because the cupronickel coding is so hard and will not flake off?
We are not really talking about a 'flaking'...it is more like molecular wear from abrasion. And yes, modern coins are not as soft as the copper and silver coins, so will take longer to wear......but they will... and I have seen some already that have significant wear. Cheers, RickO
Friction will occur on a coin's high points on each side, because those points are more likely to come in contact with other objects. The non-high-points are somewhat protected by the high points from such contact. Clad coins generally don't wear down to the copper core because the surface layers have considerable depth themselves.
that last op comment makes me want to pocket piece a zincoln to see what happens .
They will wear down to the zinc.
I have several that I have carried for a year or so, and that's all it takes.
today's photos
notice the loss of detail along the hair part.
So that's about 2.75 years of wear.
Weigh some old coins. They sometimes lose 20-30% of their original mass. The outer clad layer on moderns is pretty thick. Its much tougher than older silver-copper alloys too.
I have seen one quarter with copper showing through the clad.... must have been in a dryer for a few cycles - or a cartridge cleaner
.... It was a 1981.....Cheers, RickO
You need to know the hardness scale of metals and their alloys. The cupro-nickel alloy is much harder than the silver or gold alloys. When the metal is harder, it wears slower.
Think about 'sea glass' from the ocean.
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