Do Twisty Caps Equal Scuffs?

[HelpingHands]

Has anybody noticed a pattern between twisty caps and marks around the edge of coins?

Looking at the £1 got me thinking.

This Falklands £1 has same cap with similar scuffs.

http://www.ebay.co.uk/itm/FALKLAND-ISLANDS-ROYAL-MINT-SILVER-PROOF-PIEDFORT-1-00-BOXED-WITH-COA-1987-UNC-/311335177791?pt=LH_DefaultDomain_3&hash=item487d05ce3f

Also some second hand Kangeroos I bought with twisty caps have black marks too. I thought it may have happened in the mint but I've never seen the same marks on coins in standard caps.

I just can't imagine caps getting unscrewed and tightened often enough to cause such marks.

[MickB]

Just picked up a couple of £1 coin silver proofs today, one being a piedfort. There's no way these twisty caps can do any damage to the coin. Afterall, they are only plastic, maybe air getting through causing toning at least.

[Pete]

As the screw threads on top & bottom have to engage they cannot come into contact with the edge of the coin so the marks are due to something entirely different.

Perhaps there is less of a seal and blackening of silver suggests some contamination, usually due to cigarette smoke in the air.

[HelpingHands]

I don't whether the RM and RAM still use these styles or if they have been phased out. If they are no longer in action there may be a reason related to the marks.