Following the advice on the boards, I ordered a 4k/8k Norton combo with Norton Lapping plate. Fresh out of the box, I set about lapping them with the grid method in the sink. 4k side laps like a charm, 8k side gives me a devil of a time. 15 minutes to 3 sets of grids off the 4k, 2 hours to get 2 grids off the 8k.

Today while working on a sacrificial Ebay razor (no shoulders), I went to lap the stones again. 4k laps up quickly, 8k not so much. Mind you I've been using the slotted side for all the lapping. Out of curiosity, I flipped the lapping stone over so the flat side was up. Now the 8k laps as fast as the slotted 4k side.

Is there a right or wrong side to a Norton lapping stone? I don't think I saw anything in the instructions about it.