You Vs NGC - 1855-O Half Dollar

Well I over graded it. I said AU55 in my head at first glance. Amazing coin

EFLargeCents - Dipping is an acidic process that attacks the surface of the metal, the lustre is produced from very, very tiny "flow lines" as the coin is being struck under tons of pressure, very fast, heats the coin up and displaces metal, allowing for the metal to move, or flow into all the devices cut on the die in a radial pattern. These flow lines when disturbed will change how the light reflects off them. whether it's from a tiny hit or a large ding that is why scratches show up shiny when new. The dipping or repeated dipping will eat into the flow lines and cause the coin to lose luster each time the coin is dipped. Too much will basically wear the flow lines down to flow nubs and light won't reflect at the same angles, dulling the coin.


I found this online from a reference, I think it explains it a little better than I can:

In the pre-machine age, coinage blanks (planchettes) were heated to just before their melting temperatures and struck between dies on an anvil to create the metal flow necessary to fill the die and impart the die's design. In the first half of the 17th century machines were introduced that created enough pressure, and therefore heat, to create metal flow. The collar was also introduced to prevent the planchette from expanding beyond its prescribed diameter. In 1838, the steam press was introduced in the United States, and this technology increased the striking pressure as well as the speed of minting.

The heat generated by a coin press literally melts the planchette for a fraction of a second. As the metal flows into the recesses of the dies, catalytic heat and oxygen in the air combines with the surface of the newly minted coin. A clear oxide film includes oxygen trapped from the moment of the creation of that coin. The effect of metal flow also creates tiny radial lines that emanate from the coin's center to the rim. Flow lines are essential to the presence of mint luster and are responsible for the cartwheel effect on U.S. Silver Dollars. In the absence of wear on the high spots of a coin's design, the existence of unbroken flow lines defines mint state condition.

copied from http://www.coinsite.com/content/art...s/CMO-AO.asp

Hope that helps explain what I was thinking on calling this one. I did nail it grade wise, my cleaning call was due to over dipping, I've had many Morgans body bagged because of a lack of original luster from over dipping. Took me quite awhile and several thousand dollars before I got decent at telling for sure. in hand it's not too hard once you know what you're looking for, via static photos online it's a lot harder. Metal flow is best seen as one cartwheels the coin under a lamp while looking at it, usually with no magnification what so ever.

The problem is coins are graded usually stronger on what the obverse is, going from what I have gathered from my own experience and seen