In reference to Rev's most recent photo...above

Please, could someone explain how the crosses can go from black to white...so close on the skelp?...

what seems to be the most simple pattern, at first glance, now looks mystifying to me...

Are mixed crosses common, and I've just not noticed it before?

Rev, Thanks for the course in damascus barrels, will there be a written test? I feel like I should have paid tuition...well, sort of...