The infrared photos were taken using an Infrared Ektachrome film. Colour infrared transparency films have three sensitized layers that, because of the way the dyes are coupled to these layers, reproduce infrared as red, red as green, and green as blue. All three layers are sensitive to blue so the film must be used with a yellow filter, since this will block blue light but allow the remaining colors to reach the film.
As an interesting side note, the film was originally produced to detect camouflage and first appeared in 1942.
Mosse’s images are not only visually stunning, but are hugely impressive from a technical perspective. Mosse was worked in medium format, using stock cut down from the 70mm Aerochrome rolls, resulting in a sharpness you rarely get from the 35mm Ektachrome.