I am thinking that the FM 1794 has a mix of Halogen added to the Xenon. Am I wrong here?
I think you are right Bill. The 1794 has a Halogen fill point, but Its not 100% pure halogen. I think you may be right about the mix. There is enough halogen to prevent blackening of the bulb, which is why halogen is used.
Metal burning off the filament redeposits itself on the filament, not the glass walls of the bulb. Making the bulb last longer, and stay bright white for its lifetime, unlike Xenon only.