Please explain to me something about proof coins

Jacques_Loungecoque

Probably a simpleton question for a lot of you, but can someone explain to me what exactly makes a proof coin’s fields so susceptible to even the slightest hairline scratching? What specifically allows the surface to be so vulnerable as compared to mint state coinage?

Or are they not really, but even the tiniest of scratches are just more pronounced given the canvas? Does the same vulnerability exist on proofs across the centuries, or is the striking process a basis for some and not others? Perhaps this will take a metallurgical explanation.

My daughter recently asked and even with decades in this hobby I simply could not answer her. I was stumped and never really thought about why.

derryb

mirrored fields are produced by highly polished dies and show damage to the coin's surface much, much easier.

lilolme

To try and answer your question here are two items. The first is describing the coin production (from US Mint). Note the information for how 'smooth' the Proof coins are attempted to be made.

The second is toward standard manufacturing surface smoothness. The Proof coins would be represented by a smoother surface finish versus the standard mint product. A DMPL Morgan dollar would be between them. In the figure below from the link I think one can see why a smoother surface would show a hairline easier.

https://catalog.usmint.gov/coin-differences.html

https://www.rapiddirect.com/blog/surface-roughness-chart/

sellitstore

Yes, you hit the answer with your second paragraph. The contact marks and hairlines are the same but show up much better on the smooth, mirror surfaces of a proof. Of course, the hardness of the metal and object causing the scratch/hairline are factors too, in how serious the impairment will be.

CaptHenway

Ever hear the expression: "...like a fly on a wedding cake?" It shows up. Now think of a normal coin as a piece of carrot cake with raisins. You would not notice the fly!
Yum!

coinbuf

Regular coins have flow lines, that creates the luster we see. On really worn dies those flow lines can become really extreme, but early or late strike it's easier for hairlines to hide and blend into the flow lines of a circulation coin. The polished and reflective mirrors of a proof coin give hairlines no place to hide.

Jacques_Loungecoque

@lilolme said:
To try and answer your question here are two items. The first is describing the coin production (from US Mint). Note the information for how 'smooth' the Proof coins are attempted to be made.

The second is toward standard manufacturing surface smoothness. The Proof coins would be represented by a smoother surface finish versus the standard mint product. A DMPL Morgan dollar would be between them. In the figure below from the link I think one can see why a smoother surface would show a hairline easier.

https://catalog.usmint.gov/coin-differences.html

https://www.rapiddirect.com/blog/surface-roughness-chart/

Wow. Some really interesting reading indeed. Thank you!

@sellitstore said:
Yes, you hit the answer with your second paragraph. The contact marks and hairlines are the same but show up much better on the smooth, mirror surfaces of a proof. Of course, the hardness of the metal and and object causing the scratch/hairline are factors, too, in how serious the impairment will be.

So often in life the answer to a question is so simple you don’t want to believe it could be so. Thank you!

Catbert

Not a stupid question and smart of you to post it here!

Morgan13

This thread needs an image!