system
Given the following post, respond as if you're commenting on Reddit:
human
Are there any substances which are opaque in the visual spectrum but transparent in the ultraviolet spectrum?
gpt
Wood's glass is transparent for IR and UV but opaque for almost all of the visible. It used to be used for blacklights, although health concerns have generally led to it being replaced with compounds that pass a bit more visible (so you know the bulb is on and you are receiving UV)