Breaks in Luster: Slider vs. Bag Marks?

The minting process is over once the coin is ejected from the press. Anything that happens to the coin after that instant in time can be considered as either contact marks, wear, or damage. So the answer to your question of -

"Does the CAUSE of the breaks in luster make a difference between AU and lower MS?" - is no.

The definition of a slider is a coin that is actually AU, but many people including the TPGs will grade the coin as MS because the luster breaks are slight/minimal. That said, luster breaks do not occur at the mint. They typically occur due to light wear either from the coin actually being circulation or from mishandling by an owner of the coin.

 

No, they do not have luster breaks. It takes more than that to make a luster break. That's why you can even get coins in change from a business and those coins will still grade MS. It takes a good bit of wear to make a break in the luster. And you can think of Morgan dollars, some of them remained in bags for close to a hundred years, and yet they still grade as MS and properly so.

No struck coin will have original planchet surfaces because they cannot. This is because that metal that you see on the high points of a coin that was not fully struck is not the same metal that was on the surface of the planchet, rather it is metal that was inside the planchet and was forced up and through the original planchet surface. The original planchet surface is obliterated when a coin is struck and that metal is replaced with metal from the inside of a planchet.

For some reason people seem to think that the original planchet surface remains intact when a coin is struck and that it just lifts up as the metal underneath it tries to flow upwards or downwards to fill the recesses of the die. Nothing could be further from the truth. Because of its cohesion properties, when metal flows under high pressure the metal on the surface pretty much remains static (in its original place) and it is the underlying metal that is forced upwards and through the original layer.

No, you will not see luster on the less than fully struck high points. But that is because luster is not formed until the flowing metal meets the resistance of the die face. It is at that point that the metal then begins to flow sideways rather than upwards/downwards and it is that sideways movement that creates the luster.

 

It's takes a bit of practice and experience, but you can tell the difference between weakly struck high points that have no luster, and a break in the luster due to wear. For one thing the metal will have a different texture, and it will be a different color. Weakly struck high points wil be a bit rougher where wear will be smoother as a general rule. And wear will be a slightly darker shade than weakly struck. But both will be a darker shade than lustrous metal.