My contribution to black spots.
A MSc student project on AgNORs.  Filter the sliver nitrate gelatin 
solution (in the dark).  Use a syringe filter.  Press hard to get the 
soln. thru' the filter. Filter comes off syringe.  Student face and 
hands, bechntop, wall tiles, photo dishes, reagent bottles, etc., 
etc. covered.
Question: is there such a condition as melanotic measles?  If so, a 
pretty student had it for about three weeks!
Russ Allison, Wales