Complex sentence: In wet-plate photography, chemicals had to be stored, transported to the field, and mixed and poured onto the plate minutes before exposure--in the dark, requiring a portable darkoom wagon or tent.
Split into simpler sentences: In wet-plate photography, chemicals had to be stored, transported to the field, and mixed and poured onto the plate minutes before exposure. And it had to be in the dark, requiring a portable darkoom wagon or tent.