I just about had a heart attack when I looked at my stitching today. It had black powder on it. So far it looks like just on the unstitched part is affected. I guess I'll be washing Lady of Shalott before she's finished being stitched (and it won't all come off if past experience is an indicator, but stitching should hide it).I've had this problem before.
In 2007 I noticed black spots on the HAED I was stitching. I couldn't figure out if it was from my magnifier or the stand, though I replaced both the magifier and bolt/nut to be safe. Now I know it's the stand because I don't use the magifier anymore. My husband says the problem is that the bolt is steel, and the nut is brass and eventually gets worn away, making the black powder. I stitch a lot, so you can imagine the amount of use this bolt and nut get.
So just a PSA if you have a Gripit stand -- check your bolts. Gripit is out of business now, or you can bet I'd be complaining. I am NOT having a good day. I want to just toss the stand in the garbage and get a new one, but I can't afford it. I'll be pulling my Walmart special out of storage.