When it comes to Mokume you can keep the change...  PLEASE, before you get frustrated and think that you can't make Mokume because your coin billet has cracks consider the issue may just be the starting point.  I have made lots of coin Mokume successfully and this last couple weeks I have been using sheet metals instead and I just want to say I will never go back to coins.  to really make a nice solid reliable weld with coins there is WAY more prep work than just using sheet metals like a pro.