The Congo Red stain is a special stain used in histology to aid in the diagnosis of amyloidosis. A polarizing filter will highlight amyloid an “green apple” color. This is modified version of the stain I developed for use in our laboratory:
Counterstain the slides in Harris hematoxylin for 15 minutes, dip in acid alcohol 1 to 2 times, rise in tap water. Blue in 0.3% ammonium hydroxide. Rinse in tap water. Incubate slides in Congo Red at room temperature for 30 to 60 minutes. Rinse in tap water, then dip the slides in 80% alkaline alcohol 1 to 2 dips. Dehydrate, clear, and coverslip.