"Among the variety of Klansman costumes in the film, there appeared a new one: the one-piece, full-face-masking, pointed white hood with eyeholes, which would come to represent the modern Klan. Maybe it was Griffith who brought those pieces of fabric together in their soon-to-be iconic form; after all, his mother had sewn costumes for his Klansman father. Or, given the heterogeneity of Reconstruction Klan costumes, maybe Griffith got the idea from another source altogether: Freemason regalia. Or maybe it wasn't Griffith's idea at all, but that of Paris-trained, Costume Designer Guild's Hall-of-Famer Clare West, who worked on the film: maybe she had witnessed confraternal processions in the streets of Europe, or just made it up.
"What we do know is that the blockbuster popularity of The Birth of a Nation gave free advertising to a traveling fraternal order organizer, former Methodist minister, and garter salesman, William J. Simmons. Simmons didn't just organize fraternities; he’d joined fifteen of them, including the Knights Templar and the Masons. The 1915 lynching of Leo Frank had inspired Simmons to form a new anti-Semitic, nativist fraternity. One week before The Birth of a Nation's Atlanta premiere, Simmons received his state charter for 'The Invisible Empire, Knights of the Ku Klux Klan, Incorporated.' He sold hoods and robes ($6.50) sewn in a local shop, wrote a handbook—the Kloran—and, in 1920, hired publicists Edward Y. Clarke and Elizabeth Tyler to launch a massive campaign that attracted 100,000 new members in 16 months."
The New Republic publishes excerpts of Alison Kinney's Hood.