How Photographic Film Works

­Color negatives are not very satisfying to look at. They are small, and the colors are strange to say the least. In order to make a color print, the negatives must be used to expose the color print paper.

Color print paper is a high-quality paper that is specially made for this application. It is made waterproof by extruding plastic layers on both sides. The face side is then coated with light-sensitive silver-halide grains that are spectrally sensitized to red, green and blue light. Since the exposure conditions for a color print paper are carefully controlled, the paper's layer structure is much simpler than that of the color negative film. Once again, gelatin plays a key part as the primary binder that holds the image-forming grains and the color-forming components (couplers) together in very thin, individual layers on the paper surface.

Let's start with a black-and-white negative and make a print. You have the choice of an enlargement or a direct-contact print. If you want a larger size print than the original negative, you will need an enlarger, which is basically a projector with a lens for focusing the image and a controlled light source. The negative is placed in the enlarger, and it is projected onto a flat surface that holds the paper. The image is carefully examined to ensure that it is in focus. If not, adjustment can be made to the lens and projection length. Once the size of the image and its focus are satisfactory, all the lights are shut off, and the black-and-white paper is placed onto the flat surface. The paper is exposed for a specified amount of time using the light from the enlarger. A latent image is formed in the exposed silver grains. This time, the densest areas of the negative receive the least amount of light, and therefore become the brightest and most reflective parts of the prints. The development process is much the same as for the black-and-white negative film, except the paper is much larger than the film, and agitation of the processing chemicals becomes more critical and more difficult. The final image is actually developed silver, and by carefully washing the prints to remove all the unwanted materials, these prints can last a very long time.