Getting ochre off

On what episode of Star Trek did Captain Kirk and his crew have
yellow ochre problems? Maybe they used it when they did some repair
work on the metal shell of the Enterprize. I know gold would have
made a good heat shield for zooming in and out of various atmospheric
conditions. Are you Trekkies hoarding all those dilithium crystals?
Speaking of the wonders of technology, have you silver casters with
the black cast problems used the antifirescale silver casting grain
yet? I just love it. I wonder if anyone out there knows the secret
ingredients in Magic Cast used in casting scrap 14K. I’ve used it too
and it works, but what’s in there? Net