[Histonet] (no subject)

[Nat Nunut]

Hi everybody!
 
I'm interested in making a Prussian Blue (Potassium ferrocyanide) staining to highlight micro vascular infarctus in human brains.
In the protocol I have, it's written that a nitric acid pre-treatment is necessary.
 
I would like to know: 
1) What nitric acid is used for in histological staining?
2) What is its function in histological staining?
 
I hope you can help me.
Thanks
 
Natalia