Steven clearly meant metals here because he talks about an alloy, not a compound. Metallic coatings are sometimes used but not as AR coatings; mirror coatings are the obvious use. Dan pointed that out by mentioning magnesium fluoride as the tradiitional AR coating material.
Actually, Steven meant no such thing.
Steven was merely being careless, because, being new to the forum, Steven wasn't quite prepared for how intricately every post is picked apart for errors such as these!
Steven has since wised up
Most modern techniques involve evapourating the metal *halide* in a vacuum. Not the metal. And yes I did confuse the method with coating a mirror as I had been involved with a problem involving damaged front silvered mirrors that week...
...but, point was, there are several types of lens coating. Magnesium flouride is usually used for all modern camera lenses. Years ago manufacturers, especially in the US (MgF2 was an exclusively German technology in WW2, wasn't it?) used other techniques, including chemical glass etching and soft coatings.
Soft coatings are still used today for spectacles and consist of dunking the lenses in coloured goos and cooking them onto the surface. Some WW2 vintage Kodak lenses were coated in this way.
Soft coatings are going to be faily easy to remove, I suspect.
Hard coatings are going to be extremely difficult.
Etched glass is probably impossible, since it isn't really a coating...
So, knowing what type of coating you have would seem to be essential before attempting any of the suggested techniques for removal, I think.
Steve