What was the primary feature of the calotype process?

The primary feature of the calotype process is that it utilized paper coated in silver iodide. This innovative technique was developed by William Henry Fox Talbot in the 1830s and marked a significant advancement in the history of photography. The use of paper allowed for the creation of negative images, which could then be used to make multiple positive copies on paper. This was a revolutionary step away from earlier processes that relied on direct positive images, thereby establishing the groundwork for modern photographic practices.

Other options reference older or different processes. For example, the use of metal plates is more characteristic of the daguerreotype process, which produced unique images directly on a polished metal surface, rather than a negative-positive system. Development in bright light isn't a defining attribute of the calotype; in fact, the process required a darkroom to develop images properly. The mention of glass plates pertains more to the wet plate collodion process, which came after the calotype and further advanced photographic technology. Thus, the calotype's reliance on paper coated with silver iodide is what set it apart and made it historically significant.