A pure inorganic tanning substance, such as basic chromium sulfate, is classified on its own chemical identity. A tanning preparation is a formulated mixture — for example, chromium salts blended with masking agents, buffers, or auxiliaries — designed for direct use in a tannery process. The formulated nature of a preparation typically requires more detailed composition documentation at entry.

Enzymatic preparations used in bating and soaking are functionally part of the pre-tanning workflow, conditioning hides before the actual tanning stage. Trade classification groups them here based on their end-use purpose in leather manufacture rather than their biochemical nature, which means importers sourcing both enzyme products and inorganic salts for a tannery may find them consolidated under the same SITC heading for statistical reporting purposes.