Then perhaps you could post proof of these supposed "red stickers". I'd be VERY interested in learning about them considering the fact I've never seen nor heard of (other than in jest) or received one on failed coins.
Books, you have made me do research at which time I found out that what I previously stated was pure urban legend. CAC does NOT sticker coins that it does not deem to be acceptable for the grade. I sit corrected.
Their red sticker (more like a sticky) that gets attached and often accompanied by a short note is when they flag a problem on the coin like PVC as a heads up to the submitter.
Yes, Iron has a specific gravity of around 7.8, mercury is 13.6. It would float real well. Only about half submerged.