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Colloidal Iron: Chemistry

The Colloidal Iron staining technique uses an acid-base reaction whereby ferric cations in a colloidal ferric oxide solution are attracted and bound to acidic mucins. The ferric ions bound to the mucins are then treated with potassium ferrocyanide, leaving bright blue specks of ferric ferrocyanide, also known as a Prussian Blue reaction.

This staining technique is sometimes coupled with the PAS staining procedure so that neutral mucins and glycogen can be demonstrated in the same tissue sample. When used in this manner, acid mucins are stained bright blue by the Colloidal Iron stain process, while  glycogen and neutral mucins are stained magenta by the PAS method.