Ultra Scarce 1940s Glenn Colorule for Testing Color Vision dansk international I believe these two date

I believe these two date to the late 19th century or very early 20th century

Beginning in the 1950s

There is a clarity and boldness to watercolor drawings in this manner that I find as good and satisfying as just about anything

which stains and etches easily

Craven (there is some debate about it from what I've read

Ultra Scarce 1940s Glenn Colorule for Testing Color Vision dansk international I believe these two dateI have found a bunch of academic papers and studies discussing the use of the Glenn Colorule, but can't find even a picture of another out there anywhere. There are records of in a few academic libraries, so I know it was produced by s explained on the box text, it was made to be used to test the color vision of observers, to test the quality of light sources, and or to demonstrate disagreement caused by "pseudo," or false, color matches. There's a