If you are using Scott's tap water sunstitute to "blue" your
smears/sections after haematoxylin, it may not be fully rinsed
away, especially from the back of your slides.  Make sure of a
good water rinse before and after "blueing" agents, otherwise you
may well have this fairly tenacious precipitate on your slides.


(I wonder if the word "precipitate" will stir any controversy!)


Russ Allison,
Dental School
Cardiff
Wales