Basement membrane hexamine-silver staining, also known as PASM staining (Periodic Acid-Silver Methenamine) is a classic method of showing basement membrane mucopolysaccharides.The tissue is oxidized by iodic acid, exposing the aldehyde groups of the mucopolysaccharides within the basement membrane.The aldehyde groups reduce the hexamine-silver to the black metallic silver, and the gold chloride transforms the metallic silver into the more stable metallic gold while making the background clearer.The sea-wave fixes and washes away the unreduced silver ions, and the sea-wave washes away the unreduced silver ions. clearer, and the sea wave immobilizes and washes away the unreduced silver ions.

Basement membrane hexamine silver staining solution (PASM) can clearly show the basement membrane, which is most commonly used in renal lesions, and is often used to observe the morphologic changes of glomerular capillary basement membrane in inflammatory injuries such as fracture, hyperplasia, folding and other changes.