Yesterday I was shimming up the saddle on one of my guitars by about 0.025" to raise the action a little without making a new saddle. The operation was a success as it cured the buzz I was getting on the B-string when flatpicking and mostly cured the buzz on the D-string (unless I dig in really hard with the pick). I used my usual technique of gluing a piece of ebony shim stock on the bottom of the bone saddle with CA and sanding it down to the correct height with 320-grit sandpaper...
...except this time to speed things along I used a Dremel tool sanding wheel because I was starting at 0.080" thick and wanted to get it down under 0.040" with a rough cut before switching to sandpaper on a marble cutting board. I did not anticipate how much finer and airborne the ebony dust would be from using the Dremel tool.
I have not felt well today and a couple times I've blown my nose and found clumps of something inky black, presumably ebony dust. I'm lucky not to be allergic to the ebony but just the general insult to my immune system seems to be enough to have me moving at half-speed and a sort of half-headache all day (the 100-degree temps outside didn't help late in the day).
So no more Dremel on ebony for me. I'll stick to the slow sandpaper method and even though that does not produce airborne dust I'll use a mask next time, too. Very poor judgment, that.