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I have thought of writing a brief note to clarify what types of photographic film in black and white were commonly used in the '30s and '40s, as there seems to be a lot of confusion about the subject: black and white films of the time were basically of three types , although the boundaries between these types were not always entirely clear-cut in practice: - Ordinary or common film ( color-blind ) was sensitive to light in the blue spectrum, violet and ultraviolet, and besides being cheaper, it only required yellow -green or red light in the darkroom. Using this film the red and yellow tones in the final print looked very dark and the clouds of a blue sky tended to become invisible, blending into the background unless a filter was used. - Orthochromatic films themselves, sensitive to the spectra blue, violet, ultraviolet, but also green and yellow in varying degrees depending on the quality and type. These films require dark red light in the development phase and while the yellow tones can be lighter in print than using colour-blind film, their hue varies depending on the quality of the emulsion and the processing, while red tones still appear dark, seen that the film is not sensitive to red light. They were often the preferred choice for portraits because of the good rendering of contrast. - Panchromatic film, sensitive to blue, violet, ultraviolet, green, yellow and red, while translating the colors into shades of gray closer to the experience of the human eye, remained also variable in the results because of its quality, conservation status and the skill of those who developed it, and it required total darkness in the darkroom. This films, however, offered a reduced contrast compared to common and orthochromatic . With all of these kinds of film the use of filters was very common: yellow and amber, in particular, often intended to diminish - with variable results - the effect of ultraviolet light, invisible to the eye but very visible on film, or to correct contrast and brightness of the final result . At the time the use of these filters was an integral part of the art of the photographer, and they were used very often. The above is an extreme simplification of the technology available at the time, and there were in fact emulsions which came "halfway" between the types described, despite being advertised and sold as orthochromatic or panchromatic. The subject would deserve much more research and I am sure I have just scratched the surface of what we could find. I hope that this may help a better understanding of how difficult – and indeed treacherous – the interpretation of colours from B/W prints can be. This difficulty also partly affects colour emulsions of the time but I must confess I have not got around to finding out what the exact differences between – say - American and German film were. Any corrections or additions to what I have written here are very welcome. Flavio