You can wrap the frizzen in old scrap leather and coat it into clay/dirt and throw it in a fire over night. fish it out in the am when it cooled.
Use Kasenit, as suggested. faster
send it off
half sole it. basically, you add a piece of higher quality steel to the face of the frizzen. I have done it with a few TC frizzens over the years. You need a piece of clock spring, or wind up toy spring the width and height of the frizzen. roughen the surface of the frizzen with real coarse sand paper (40 grit) and also the back side of the clock spring. then epoxy the two rough edges together and clamp it tight for 24 hours. Slowly grind the edges of the spring back to match the edges of the frizzen face, being careful not to heat up the spring. After nearly twenty five years, my brother still hunts with a TC hawkens that I half soled that way back then. Clock spring is usually only about 1/64th inch thick and is a much better steel for sparking than the steel used by TC then for frizzens.