It's the blistering summer of 1946 and the 90-degree heat isn't exactly fitting for a wintry scene. You need to cover the fictional town of Bedford Falls - which happens to be one of the longest sets ever made for an American movie - in cheap fake snow that makes too much sound for you to record dialogue.

These are the challenging circumstances director Frank Capra found himself in when he was making what would become one of the most treasured Christmas films of all time, It’s a Wonderful Life.

The industry standard 'snow' at the time was simply cornflakes painted white

Within the narrative the snow acts as a pivotal plot device: Jimmy Stewart's character George passes through a snowstorm as he returns to reality after his whirlwind journey with Clarence, his guardian angel. But the snow used in the production has its very own story to tell.

The industry standard 'snow' at the time was simply cornflakes painted white. This made loud crunching noises as actors moved across it, meaning that dialogue would have to be dubbed in at a later date.

But Capra wanted to record the dialogue live - and the solution he concocted with his head of special effects, Russell Sherman, would go on to win a Technical Award from the Motion Picture Academy, and allow filmmakers to produce a realistic onscreen snowfall for the first time ever.

Sherman's team mixed foamite (the material used in fire extinguishers) with sugar, water and soap flakes. This solution was then pumped at high pressure through a wind machine to create the look of freshly fallen snow on trees, streets and in drifts against buildings.

In all, it took 6,000 gallons of this new pseudo-snow to cover the four-acre Bedford Falls set. This included 75 stores and buildings, a tree-lined centre parkway with 20 fully grown oak trees, a 300-yard main street, a factory district and residential areas.

Just in case the foamite ran out, Capra and his team had a backup plan, as notes from the set point out: "Dolomite [a translucent mineral] and asbestos were other old standbys used to dress the set." Health and safety has come a long way since then.

It’s a Wonderful Life was the first and only film Frank Capra had produced, financed, directed and co-written - and the ingenious fake snow was just part of the magic that made it a Christmas classic.