Notches
Sheet films have notches cut into one short side. This makes it simple to determine which side is the emulsion, when the film is hidden from sight (in the darkroom, or inside a changing bag). When holding the sheet in "portrait" orientation (short side up), with the notches in the upper right, the emulsion side is facing the photographer. The notch patterns vary in size and layout; each type of film has its own distinct pattern, commonly referred to as a notch code, to enable film type identification.
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