I just got a set of Narex Richter Extra chisels and boy do they look great! However, when I've been trying to flatten the backs I am having an issue getting them flat. In particular the 1" chisel has been giving me a lot of grief trying to get it flat near the cutting edge. I've been marking it with a sharpie to see where the low points are and part of the cutting edge doesn't seem to be wearing away. Once it is worn away I re-mark it to make sure that its flat and that same section stays marked when the rest of the markings go away nearly instantly. I know that the part near the tip is the most important and I'm not trying to flatten the whole back, but I've spent 3-5 hours on this one chisel alone and it still isn't flat.
I'm was using 150 grit sandpaper on a granite slab and then stepped up a 325 grit diamond stone, but it is still giving me trouble. Is there something that I am missing? I don't think that one chisel should take this many hours to flatten.
Thanks in advance for any help!