[R-390] Level/VU meter luminous phosphor type?

[Chris Farley]

A probably weird inquiry for the brain trust..  
Is anybody aware, or aware of a doc/spec denoting what phosphor type(s) were used for these meter indicators?  Obviously this would not be unique to the R390 family of equipment, and differing blues and greens are seen.  The question is also raised how instrument luminescence was called out or qualified.  
I've long been morbidly curious exactly how the old radium paints were actually made, and what phosphor types were used.  I've done some brief searching over the years and never really came up with anything conclusive. 
Regards, Chris 

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