After staining a piece of poplar a series of subtle, regularly spaced cross-grain markings appeared on the factory cut faces (I've attempted to make markings more visible with the green indicators):
It was not on every board, only a few. I sanded the wood smooth first (and put down a probably-inappropriate coat of shellac), and the markings were not visible to my eyes prior to staining or when the stain was wet. They appeared as the stain dried. There are 4 markings every 1-1/8".
I tried applying a second coat but it still did not hide them.
My question is: What are these from and how can I either hide them, prep the wood before staining to eliminate them, or determine if a board will have them ahead of time so I can avoid using it?
I am assuming they are artifacts from how the board was cut at the factory. My only thought is perhaps as a rule I could trim all factory edges off all boards on the table saw ahead of time, but this seems cumbersome.