As I've mentioned before I use diamond paste on iron and/or mild steel honing plates for some sharpening, and particularly for flattening blade backs.
One issue that arises often is particle control, whether due to initial surface quality, contamination over time, or after lapping the plates. This issue recently came to a head for me when I added a new cast-iron lap (from McMaster) to my rotation, and it seriously scratched the first tools that I tried it on (thankfully not good ones).
One obvious way to deal with this is to rub the plate with an "eraser" of some sort. The ideal eraser would be softer than the plate but hard enough to hold the abrasive particles. I chose to use two in sequence:
1. White ScotchBrite pads (the kind with the least/finest added abrasive). These are commonly used to remove abrasive grit and "hairs" from ski bases, and it turns out that they work fairly effectively on lapping plates as well. They helped, but weren't sufficient to achieve scratch-free results.
2. A 1/2 hard 110 Brass bar. At Rockwell B40 this is significantly softer than either cast iron or mild 1018 steel. This appeared to remove basically all residual protruding rogue particles, leaving mild scoring as evidence of their passage (the brass begins to lap the iron/steel with the newly "captured" particles. The brass bar can then be filed to remove those before using it on another plate).
I get scratch-free lapping performance with submicron diamond compounds on plates that have been given this treatment.
Full soft 110 brass (Rockwell F40) would probably be better still, but costs significantly more. I wanted to test the concept with cheap 1/2-hard material before going overboard with it.
I'm sure somebody like George will point out that this is a common strategy among knowledgable machinists. It's obvious enough that it has to be :-).