First, I advise against developing the rolls from your trip. Beginners face numerous pitfalls, and what can go wrong will go wrong. Having said that, it’s lots of fun to develop film, so go for it -- just select sacrificial rolls until you get past the learning curve.

Now about developers: All developers are reducing agents, they reduce (split apart) the light sensitive salts of silver that are the goodies that make film work. Film consists of a transparent plastic base, over coated with a gelatin layer. The gelatin acts like a glue; it holds the light sensitive goodies in place. These goodies are crystals of silver plus a halogen (Swedish for salt maker). The halogens used are bromine, chlorine and iodine.

The silver halogen crystal is relatively stable if care is taken to prevent it from seeing light energy. When the shutter of the camera clicks, an image of the outside world is projected onto the surface of photographic film. Light energy bombards the film. The brightness of this light and shadow image is proportional to the vista being recorded. Thus, the silver halogen crystals receive photon hits and each hit weakens the bond that binds the silver to the halogen. The camera exposure is insufficient to fracture the crystal, however the tying bond is weakened.

When the film is submerged in a developer solution, the silver halogen crystal is tested. If the bond is weak, the developer reduces (separates) the crystal into metallic sliver and a halogen. The halogen is water soluble; it dissolves into the developer, which is mainly water. It is the liberated metallic sliver that comprises the image, as this metal is opaque, as such it appears black. When the developing step is completed, an image has been formed. The metallic silver is present in proportion to the brightness of the vista.

There are countless different developing agents available to do this task. The developer you select will likely be comprised of combination of metol and hydroquinone. Either can be used however most developer formulas contain these two in various combinations. Metol yields images with softer contrast whereas hydroquinone yields higher contrast. Most fine-grain developers (allow superior ability to enlarge) contain solvents or other means to reduce the size of the metallic silver fluff that make up time image. Again there are countless combinations, each has advantages and disadvantages.