2921.42.55.00 - Fast color bases

This HTS classification, "Fast color bases," encompasses a specific group of aromatic amine derivatives used primarily as intermediates in the production of dyes and pigments. These compounds are characterized by their ability to readily couple with diazonium salts to form azo dyes, which exhibit excellent fastness properties (resistance to fading from light, washing, etc.). The "fast color" designation highlights their utility in applications where color stability is paramount, such as in textiles, inks, and plastics.

As a subcategory within "Aniline derivatives and their salts," this heading specifically isolates those compounds whose principal application and chemical structure lend themselves to the formation of fast-dying agents. While other aniline derivatives might exist with different functional groups or intended uses, "fast color bases" are defined by their reactivity in azo coupling and their contribution to dye fastness. The "Other" designation at this level indicates that this category is for fast color bases not otherwise specifically enumerated in preceding subheadings.

Given that this is a leaf node, there are no further subdivisions. Classification within this heading relies on confirming that the chemical substance is indeed an aniline derivative designed for use as a fast color base, often determined by its chemical structure, CAS number, and documented industrial application.