RUBY WHAT? AMBER WHO?

I used to get asked all the time about Rubylith/Amberlith. What is it? How is it used? Who still uses that stuff!? etc....

Well, fret no longer. I recently happened across this beautiful piece of vintage Ulano instructional material that explains it, once and for all.

("It's the NEW hand-cut masking film for the graphic arts!" ahhahah)