Ammonium Thioglycolate

Ammonium thioglycolate is the active ingredient in color-change wheel cleaners (SONAX Full Effect, Iron-X, etc.). It reacts with iron oxide (brake dust) to form a purple iron-thioglycolate complex — giving you visible feedback that the product is working. The distinctive sulfur smell is unavoidable — it's the same chemistry used in hair perms. Wear nitrile gloves (it's a skin irritant) and avoid spraying into the wind. The purple runoff should go to a sanitary drain, not a storm drain — the compound is moderately aquatic-toxic before it breaks down.