Basic chromium sulfate and other chromium-based tanning salts are inorganic tanning substances and fall under subheading 320290 when put up as tanning preparations. However, pure chromium sulfate as a defined chemical compound may be more specifically classified in Chapter 28. The determining factor is whether the product is presented as a tanning preparation or as a pure chemical; importers should review the Chapter 28 and 32 notes and consider a binding ruling for borderline products.

Enzymatic preparations used specifically for pre-tanning hides are classified in heading 3202 (subheading 320290) by virtue of their specific use in the tanning process. General-purpose enzyme preparations not put up for tanning use fall under Chapter 35. The intended use and presentation of the product — including labeling and commercial documentation indicating a tanning application — are the key classification factors.