Amyloid is an extracellular eosinophilic substance with no fixed shape, which can be found in different tissues and organs, resulting in a disease called amyloidosis. Amyloid is mainly composed of proteins, most of which are arranged in a reverse β-folded layer structure, and amyloid is arranged as protofibrils in electron microscopy, with a large number of extracellular unbranched filaments, mostly randomly arranged in the case material. The histological methods used to identify amyloid are methyl violet staining, Congo red staining, polarized light microscope observation, etc. Current research has found that the traditional methyl violet staining method is low in sensitivity and poor in specificity, and the classic and effective method is Congo red staining. In 1922, Bennhold found that Congo red could be used for the identification of amyloid in vivo, and it was applied to the tissue sections, and later improved by later improved by Highman, the staining effect is better.

The amyloid staining solution (modified Stores Congo red method) mainly consists of Stores Congo red staining solution and hematoxylin staining solution. Stores Congo red staining has no differentiation step, but the preservation time is shorter.