The back of a napkin

Am new to etymology and trying to find the history of the phrase "back of a napkin" Anyone know it or can give me a process for discovery?

Regarding my own process regarding finding the origin of a phrase, I mostly depend on a small library of reference books, online sources (including this site) and my own recollections. I don't know about scholarly research. Looks like that involves interviewing people and recording information about when they heard the phrase and where, etc., and searching/scanning old newspapers, letters and books for references to phrases.

May we safely assume that you understand what is usually understood by the phrase, "back of a napkin"? If so, you are asking, who first used the phrase, to which there is undoubtedly an answer, but one that will be hard to find, if not impossible.
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