I want to know the answer to the following question:
Exposure to what natural element was necessary for early photographic plates?
All the background I'm provided with is that "Many hours of exposure in the camera were required, making bitumen impractical for ordinary photography, but from the 1850s to the 1920s it was in common use as a photoresist in the production of printing plates for various photomechanical printing processes.[not in citation given]". Is that enough to answer the question?
Answer: no