[Histonet] pigment in bone marrow clot sections

[Mike Pence]

I need to ask if anyone has seen this before? In our bone marrow clot
section that we stain H&E, I am seeing black precipitate that looks like
you were looking at anthracotic pigment.  This is at the same level as
the section on the slide. It is not debris it is only on the stained
section (the rest of the glass looks clean) and we fix in 10% NBF.  It
is not zinc, like we use to see in B-5 fixed tissues. We only see it in
very bloody specimens like bone marrows or blood clots.  Has any one
else see this or know what it is or how to get rid of it?
 
Thanks in advance,
Mike