What are these lines I sometimes see in BU/proof coins?

[pendragon1998]

I've occasionally come across these lines in coins which radiate outward from the center. They're often in proof-like or proof coins. They're not cleaning or circulation hairlinesm as the coins I've seen them in haven't been cleaned or circulated. Are they some form of stress pattern in the metal from the striking process? Here's a detail from a photo Mark Goodman posted (left) and a bad photo I took of a proof-like SBA dollar (right).

 

[Amanda]

I asked in Mark G's Guess the Grade thread what they were, and Mark F. said they were flow lines.

 

I see two different kinds of 'lines' that I am not sure about.

 

First I see lines or marks that seem to radiate from the central devices to the rims, and they are all parallel to each other.

 

Then I see random thin lines in the fields that go every which way.

 

Amanda, I think you first described evidence of metal flow (flow lines) and next, die polish lines and/or hairlines.

 

-Amanda

[TomB]

From the striking process.

[bsshog40]

I actually have the same thing happening to my ben franklin proof. The pics shows how it kind of looks like a blue color but it also has the lines streaking across the front.

[bsshog40]

I have a better pic of what this problem is. What do you mean the stiking process? I've heard this is hazing and can decrease the value of a coin.

[pendragon1998]

Hazing is essentially light toning - a chemical change on the surface of the coin. What I'm talking about are lines of metal fatigue related to pressure imparted during the striking process.

[CarlWohlforth]

The lines on the SBA are what Amanda said, flow lines. They come from the minting process as Tom said. They are not haze like on that modern commen and that is a different thing.

 

The metal moves during the striking process. The fields are the low part of the coin and have the most moving metal.

 

You can see another example of flow lines on mgoodm's proof Mercury dime on another thread. I would like to buy proof Mercury dimes that have no flow lines. Proof Walkers usually have flow lines too.

[WoodenJefferson]

If I'm not mistaken, the obverse of the coin will show more prevalent flow lines than the reverse because the lower die is already raised and into position and is stationary prior to the obverse die striking the planchet. The flow lines from microscopic to the visible create the “cartwheel” affect seen on the minted coins surface.

 

Striking visible flow lines like the ones shown usually only happen in vertical presses (as used in proof minting) and does not readily occur on the horizontal presses where equal striking forces oppose one another.

 

Just an observation…could be totally off, memory fades with age.

[mgoodm3]

I think that the flow lines are a form of die deterioration related to the movement of metal during striking. More and more cartwheel luster will show up as the die ages. The mirrors get shallower at the same time.

 

Early

 

 

mid

 

 

Later

 

[MAULEMALL]

 

Damn thats a Fine coin...How much doubling is There?

[mgoodm3]

Around the lettering? That doubling is just a die prep characteristic called Longacre doubling. For whatever reason they cut a shelf around the letters. Shows up on many of Longacre's stuff.