Film Developing by Nathan Jones

The following three part article by Author and Photographer Nathan Jones is tailor made for the do it yourself from home photographer.

Developing B&W Film at Home (Part 1)

“Fall Tedium” (Rolleiflex 6006, 80 mm f/2.8, Fuji Acros 100)
Introduction
If you’re reading this, you know the truth: film is back, baby!
The first step in developing your own B&W film at home is not to be intimidated. The procedure is fun, rewarding, inexpensive, and a lot easier than you think. In doing it, you move one step closer to taking responsibility for your entire picture-making process, from pressing the shutter release button to having a glossy print in your hands.
You could go ahead and develop film without any understanding of how the process works and get great results nonetheless. However, I feel that it’s more satisfying to know a little about what you’re doing and why. A basic knowledge of how film-based photography works is therefore quite useful.
Photographic film is coated by an emulsion that contains microscopic particles of silver halide — basically a silver-containing salt, which is very sensitive to light. When you press the shutter release button, light passes through the open aperture of your camera and is focussed by the lens onto the film. When a ray of light strikes a particle, a small proportion of the silver halide is reduced to metallic silver. This forms the “latent image,” which is much too faint to see, and must be enhanced by developing.
Let’s imagine that you’re photographing starry skies at night. The figure below illustrates in carton fashion what happens on the film when you press the shutter release button. In this series of images, the aquamarine colour indicates silver halide, and the pale grey denotes traces of metallic silver in the latent image.

When you add “developer,” metallic silver in the latent image catalyzes, or accelerates, the production of more silver by reduction of silver halide in the immediate surroundings. Thus, areas of the film that have been exposed to light (bright parts of the scene) are amplified (i.e., more and more silver deposits there, making them black — you’re making a negative, remember?), while the areas that have not been exposed, are unaffected and remain as silver halide. This developing process can only occur in an alkaline environment; it is arrested by making the system acidic. Developing is typically halted by the addition of dilute acetic acid, also known as the “stop.”
We have now amplified the trace silver to visible metallic silver, thus:

At this point, the film is still sensitive to light as it contains islands of “developed” silver surrounded by seas of undeveloped silver halide. In order to render the final negative, these seas must be washed away. To do this, we use a chemical known as the “fix.” The fix contains an agent that solubilizes the silver halide, but leaves metallic silver intact. Once the fix has done its work, all we have left on the film is silver metal. This silver will be deposited only in areas of the film that have been exposed to light (rendering them black); those areas that have not been exposed to light will be colourless.
We now have the final negative, which is no longer sensitive to light:

Thus, the process consists of three basic steps:
(1) Develop — amplify the latent image by converting exposed areas of silver halide to silver metal.
(2) Stop — bring an end to the developing process.
(3) Fix — wash away all remaining silver halide to render the final negative, which is now insensitive to light.
In the next installment, we talk about the equipment and chemicals you’ll need. Go ahead and read Part 2, Preparation.