Are these "Lathe-Lines" on this medal??
I was looking at some archived medals this morning trying to sort out some planchet type questions and ran across an 1870 Pilgrim HK-13 which I had never seen before. The medal is quite striking in appearance but what really caught my attention are the circular lines which are clearly visible on the reverse of the medal. I've included a link to the NGC cert page to allow viewing the medal in the holder, but it doesn't appear that the lines are on the plastic. I've seen this before and have a few medals with the same appearance, raised circular lines that are part of the design and flow uniterrupted over the other design elements/lettering. If you can offer a good description of how/why this sometimes occurs, please do. Post an image if you have one.
Thanks in advance.
NGC cert page link --- https://ngccoin.com/certlookup/3740160-013/67/