UV light is attenuated by ozone and water vapour in the air and by normal glass. In the case of glass, attenuation is determined by composition and thickness so some varieties are better at blocking UV than others. As the UV is only attenuated it could mean that damaging levels may still pass through so don't think of glass as an impenitrable shield. Just remember the masks that arc welders use !
Quartz optics are used, as opposed to glass, in vacuum when working with UV in laboratories to minimize this attenuation.
Black matt paint should absorb UV light with minimal reflection.