Green’s Dictionary of Slang

unadulterated, esp. of drinks.

1861		Roscommon & Leitrim Gaz. 30 Nov. 4/1: Well I'm blest if ever I could ‘diskiver’ what was the fancy of drowning good hot hollands with water; give me the stuff stark naked with the jacked off, that’s my religion.
1877		Pittsburg Post-Gaz. (PA) 31 Mar. 2/2: It is stark naked, unadulerated rascality.
1921		(con. WWI) E. Lynch Somme Mud 112: Real stark-naked bullock-driver abuse it is.
1936		Western Mail 14 May 9/7: Every sapeech in support of the report was a stark naked confession of personal vendetta and malice against the Recorder.
1950		Philadelphia Inquirer (PA) 13 Jan. 5/4: ‘It ought not to be hard to get the stark naked, unadulterated facts’.