In the examination of tissue for amyloid the most reliable technique is detection of the characteristic birefringence in polarised light exhibited by sections stained with Congo red or Sirius red.

When stained with Congo red and observed under polarized light, the amyloid has a characteristic "apple green" birefringence as seen here in a deposit around an artery in the heart.

Under the UV-light, effects of oxidants and metal ions on the photochemical reaction of congo red were studied by static method.