Early cameras were cumbersome, costly, and often required specialist knowledge of the devices and developing chemicals to use them correctly. Early film development processes, like tintypes and daguerreotypes, relied on potentially dangerous chemical interactions that were best handled in a controlled environment. For daguerreotype images, popular between 1840 and 1860, the photographer put a sheet of copper, coated with silver and exposed to iodine vapor, into the camera. Once the sheet was exposed to light during the taking of the picture, the photographer used a mercury vapor to bring out the image, and then set it with salt.