Compounds with a phenol group will form a blue, violet, purple, green, or red-brown color upon addition of aqueous ferric chloride. This reaction can be used as a test for phenol groups. Mix several ...

Metals with extremely low rates of allergic patch-test reactions included zinc, ferric chloride, and tin. Reaction rates varied depending on metal salt, concentration, and timing of readings.

Ferric chloride works as well ... making up etching solution from powdered ferric chloride. But the meat of the video below is the head-to-head test of three different masking methods.