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Message:: [QUOTE="Rob Woodside, post: 3116006, member: 96187"]Thanks so much Jim. I've observed flow lines in 8 Reales pieces, but on a much larger scale that really do look like a flow, quite different than these subparallel tiny rills. These are exactly the kind of "mountains" I was expecting. So mint lustre is the sheen from the specular reflection off the flow lines. That helps a lot!!! If you drop a particle into a flowing fluid of the same density, the particle will trace out a flow line as it moves with the fluid. I suspect the actual flow of metal during striking is perpendicular to the tiny subparallel rills and these rills form like surface ocean waves due to an uneven flow. I'm rapidly coming to the conclusion that apart from coatings, including amalgamation, wear is the only way to destroy mint lustre. The abrasive lines I'm expecting with cleaning may be just too small to see with the naked eye or even 40x available to me. If that's true, how do the graders tell the difference between a "light cleaning"  and almost no wear? Do they look at coins at 400x or more where the characteristic abrasive scratches from cleaning should be obvious?[/QUOTE]