Wet blue production (so called because the semi-finished hide is given a chrome bath which imparts a blusih tint).

This process involves removing unwanted substances (salt, flesh, hair, and grease) from a rawhide (by soaking in a bath of lime and sodium sulfide to dissolve hair and flesh), trimming it, treating it to impart the desired grain and stretch, and finally soaking it in a chrome bath to prevent decomposition.

This step is far more polluting than finishing, generating 90% of the water pollution associated with leather tanning.
Finishing – Finishing involves splitting, shaving, re-tanning, and dying the wet blue.