"My experience in shooting 'Scott of the Antarctic' proved highly valuable when it came to shooting many of the scenes staged in the snow and snow storms," said Cardiff. "I'd become familiar enough with various snow scenes to be able to recreate the effects I wanted. But sometimes I was just lucky with the location. When we shot on the banks of the Arno river, for instance, there was a slight fog which offered wonderful pictorial possibilities. But we also had to create snow and winter aspects for some of the scenes. Actually, a large proportion of the film was shot during the height of the Italian summer, when almost every Roman desserts the capital to escape the relentless heat. To photograph an important winter scene at this time, it became necessary to scatter powdered plaster over a square-mile location site to give it the appearance of frost."
"In August," Cardiff continued, "we couldn't get the Cine Cita stage space we wanted, as Metro-Goldwyn Mayer had booked it for its production of 'Ben Hur,' which had not yet even been started. So we were obliged to take space in a tiny studio across the road. It was so small that our one set came to within a foot of the walls on every side. Luckily, fire restrictions in Rome are less severe than in Britain."
"By this time we'd lit this set, the temperature was practically bursting the thermometer. And on top of this, the interiors we were shooting were supposed to be mid-winter scenes in which members of the cast had to wear fur coats and appear to shiver in the cold! The floor was literally soaked with perspiration before we began rehearsals."
In all the 'exterior' snow scenes which were actually shot in the studio, Cardiff used a panel of glass, sprayed white, plus a pale green filter before the lens in order to impart a slight mist effect to the scenes. One sequence in the picture, which has attracted much praise for its photographic excellence, is the action of the duel in the snow. Many expert photographers have unqualifiedly declared these scenes actual exteriors. The fact is however that they were shot on Stage 5 at Rome's Cine Citta studio. To achieve the very real effect of dusk on a wintry night, Cardiff used a glass before the camera with sky painted on the upper portion, as the wide-angle lens used in covering the great sweep of the set took in too much vertically.
Though this is a technique which Cardiff has used before, it was new to the Italian technicians, who were rather dubious about the outcome. For a sun effect in the same sequence, Cardiff employed an original trick of directing a lamp onto the sky area of the painted glass mounted before the camera lens. A combination of colored filters plus a fog filter gave Cardiff the effect he sought, and resulted in one of the most talked about scenes in the film.
Jack Cardiff: Fake Snow
From the article, Jack Cardiff's VistaVision Venture by Derek Hill, American Cinematographer, December 1956