[Idiom] BLOWN IN THE GLASS CLINCHER : what does it mean ?

[Ron Wolpa]

From the noir movie Nightmare Alley (1947) , I heard the expression : BLOWN IN THE GLASS CLINCHER.
What exactly does it mean ?
Thanks.

 

[JMurray]

not a teacher

blown-in-the-glass = genuine, authentic, trustworthy.
blown-in-the-glass : Green's Dictionary of Slang Oxford Reference

clincher = a fact, argument or event that is decisive or settles a matter.
clincher - definition. American English definition of clincher by Macmillan Dictionary

a blown-in-the-glass clincher = something that is genuinely decisive and settles a matter, for example an argument or contest of some sort, or ensures a success.