Monday, June 22, 2009

"Real" Darkroom Photography (Part One)

When I was a kid, I used to watch a TV show called Mission Impossible. Inevitably, one of the main characters would spend time in the darkroom developing film to incriminate the criminal-du-jour. Have you ever wondered how that process works? Well, in this first segment, I'll explain how a latent image is captured on film and how the developing process works.

Many years ago, I was fortunate enough to have a class in darkroom photography when I was in school. After that, I set up my own darkroom in a spare room that used to be the garage. The process was so fascinating to me. Now, in the age of digital cameras, that knowledge is getting a bit scarce.

There's Jello inside?
Inside the metal canister is a roll of plastic which is coated with various layers. One of these layers is a special form of gelatin (the exact same chemical you can eat at desert!) Suspended in this dry gelatin are microscopic with silver-halide crystals. These crystals act as light detectors and change chemically when hit by photons. Areas of the film that were hit by bright light will contain large numbers of activated silver halide coating. Other areas which have not been exposed to bright light will not contain many activated crystals. Its important to note that the film contains only a latent image at this point. That is to say that the activated areas look exactly the same as the un-activated areas but their chemically different. The silver-halide crystals are amazingly stable and can hold their state (activated or not) for a long time. To render the image, we need the next step.

The Developer
The developer is a fluid that replaces the exposed silver halide crystals with pure silver. This chemical reaction takes place in a light-tight canister in which the film has been placed on a spiral spool. The spool is needed to keep the film surfaces separated to the developing agent can do its work. The film sits in the tank for about 12 minutes depending on the temperature. The higher the amount of activated crystals, the more silver you get in that spot, and the darker the spot will appear in the end.

Whoa! Stop
If left in the developer for too long, the remaining unexposed silver-halide crystals would start to be affected. To prevent this you add something called the "Stop Bath". This chemical would stop the developing process before it began to eat up the rest of the latent image on the film. 30 seconds is all the time it takes for the stop bath to do its job.

The Fixer:
In order to make the image light durable, we need to remove the unexposed crystals using something called fixer. Generally this liquid dissolves away those crystals that have not become silver metal so that subsequent exposure to light doesn't activate them. The film soaks in the fixer for about 3 minutes. Now the image can be viewed. The image on film will appear as a negative of the image that was shot because bright spots = lots of exposed crystals = lots of silver = a dark area on the developed film.

Sticky Stuff
Remember that the film has coating of gelatin on it? This stuff is pretty sticky when it's wet and needs to be dried thoroughly before it can be handled. I used to have a clothes line strung out with a clothes pin on the top and bottom to keep the film from curling back up. Once dry, the film can be handled, but can still be scratched fairly easily.

There's some great further reading from Illford on the whole process

That's it for now. In the next segment we'll take a look at how the negative gets printed.

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