This Anglo-Mexican co-production was shot in Pathécolor, a system similar to Eastmancolor that joined the three basic colour emulsions in a single negative. The process was quite expensive when it came to making copies, the quality of which was not always guaranteed. This led to both producers insisting on having an original negative and as the only way to have two originals was to shoot every scene twice, that is what happened. Comparing the two originals shows the differences between the Mexican and English versions of the film.

Ferrán Alberich