He wanted real snow – not the painted corn flakes Hollywood was accustomed to passing off as the white stuff – to blanket his setting, the town of Bedford Falls, reports Life.com in its special feature with never-before-seen on-set photos from the holiday classic.
To achieve his goal, Capra – who trained as an engineer as a student at Cal Tech before becoming the talkies' first true stylist, as an Oscar-winning director for Columbia Pictures – collaborated with RKO studio's special effects expert Russell Sherman.
Together they created a product that quelled the crunch of cornflakes and replaced it with their own gentle falling (and sounding) snow to cover the fictional town where James Stewart's George Bailey helped affect the lives of everyone around him.
Their recipe? Mixing Foamite, a material used in fire extinguishers, with sugar and water – or, say some accounts, with soap flakes.
Martha Holmes / Time & Life Pictures / Getty
Most surprising of all, the snow scenes were shot on a series of 90-degree days in June and July 1946.
Still when It's a Wonderful Life first opened, it didn't set the box office on fire, or even warm the hearts of critics. Subsequent TV showings made it the hit with audiences it is today.
As Capra, who died in 1991, said about the picture in his 1971 autobiography, just as the reputation of his movie was being revived: "I didn't give a film-clip whether critics hailed or hooted Wonderful Life. I thought it was the greatest film I had ever made. Better yet, I thought it was greatest film anybody ever made … my kind of film for my kind of people."