What a great observation. Thank you for bringing this up. I'll look at all my pipes with visible grain again and see if there are shadow growth rings. Pretty interesting. At a much more trivial level, I feel like some inexpensive pipes have the stain applied so that it looks like grain. When I mentioned this before, it was booed down, but I believe I've encountered that here and there, mostly in pipes I didn't buy. One or two suspects on the racks that earn their keep as choice smokers anyway.