Leather is tanned by cross-linking collagen with tris(hydroxymethyl)phosphine or a condensate of a tetrakis(hydroxymethyl)phosphonium salt with an amide or amine in a main tannage or retannage.

O couro tanned pelo collagen do cross-linking com tris(hydroxymethyl)phosphine ou por um condensate de um sal do tetrakis(hydroxymethyl)phosphonium com um amido ou um amine em um tannage ou em um retannage principal.