Some of the material I cut ends up with a layer of soot on the cut edge. Some material does not.
I think it depends on the type of glue that was used to create the mdf or plywood.
I have found an unlimited free source of 2.7mm plywood (in 7"x48" pieces) and was looking forward to using it for prototyping parts. (If you are near PDX check the craigslist free section for meranti plywood, the source tries to post every week)
The problem is, this is material that leaves a layer of soot on the cut edge. When working with it soon my hands are covered in soot and there are dirty fingerprints everywhere.
I have not been pleased with the solutions Google found for me as they involve using water or too much work. Until I stumbled on a dry cleaning sponge. It looks like a sponge, but is made from rubber and is used dry. It is reported to work really well and picking up soot.
I ordered one and found that it works pretty well. Light rubbing with the sponge on the edge of the part seemed to remove about 95.3% of the soot. After cleaning and assembling my part, there is some soot on my fingers but not enough to get anything dirty.
If you are struggling with soot, you might check this out.
Theoretically, You can clean the sponge with soap and water and then once it dries out use it again.