What are HR and AR coatings made of?

[Blackwolf]

Wikipedia had a pretty good explanation. I was wondering about the exact makeup and how to change what wavelengths it works on

 

[Bionic-Badger]

They're usually chemical depositions of specific thicknesses. You'd have a hard time changing them without access to the chemicals, a lab, and the necessary expertise. You can read more about them on here and other optics sites.