Hi Dr. Grabsch,
What you are seeing might be hematoxylin precipitate.  When it (hematoxylin)
begins to break down, it leaves dark precipitate sort of like you describe as
little trees.  Try some new hematoxylin.  Hope this helps.
Shirley Powell
Mercer University School of Medicine
Macon, GA

Heike Grabsch wrote:

> I am a learning-by-doing-histotechnologist (I am a resident (medical
> doctor) in pathology and now have to do my research work by myself,
> because my technician is pregnant)and I need some advice:
>
> what can I use instead of hot running tap water for blueing the tissue
> sections after Mayer's hematoxylin? Our hot tap water is really ugly
> brown and it takes "hours" until it is clean.
> Today I tried 0.5% lithium carbonate for 30 sec. The colour is very nice,
> however I have got a lot of "arbored" precipitates (like small trees, if
> you understand what I mean) on top of the tissue, I washed and washed
> with buffer, with dist. water, with dist. water and Triton X, but I could
> not get rid of this precipitates. What is the problem with lithium
> carbonate as a blueing solution? Or may be it is the concentration?
> Any suggestions what to use instead?
>
> thank you for your help,
>
> Dr. Heike Grabsch
> Dept of Pathology
> University of Duesseldorf
> Germany