The paper came already coated as already said. The package looked like a giant version of a ream of today's Xerox paper, except one side of paper was faintly yellow or blue.

I *think* it's ultra-violet sensitive. I don't recall paying any particular attention to light sensitivity while handling it but I also recall putting some objects on it and leaving it out under direct sun for few minutes to get images of the objects burned in.

It was at least 35 years ago.