Happens with Paulson bright white though.
See these two. When you see the edge spots looking like that it means there are just a few microns of insert clay left.
(Some will come out of the press with the edge spot completely gone - and usually be spotted by QC and rejected - rarely they are missed and that is how insert errors occur - if one weak spot is found the body clay can all go out through that opening and all the other spots are unaffected).
.

.