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Expose your plate - the ISO of the plate will depend on your chemical mixture, but start thinking from about ISO 2 or 3
To develop the wet plate you do not need a lot of developer. For a 5x7 plate roughly 14 ml will do the job.
Like coating a plate, developing is also done in 1 fluid motion, and anywhere the fluid halts, you will get differences in tone and contrast.
Developer is a mixture of the following:100 ml distilled water4 grams ferrous sulfate6 ml glacial acetic acid4 ml grain alcohol
Pour on the solution and make sure it get all over the plate. You are not using a lot so pouring off excess should not be needed. Count to 15, at 10, you should be able to see an image appear, at 15 you should pour regular water over the plate to halt development.
The hardest part here is trusting yourself to have taken the image correctly and NOT let it develop any longer (unless you diluted the developer) - any longer development will result in loss of contrast and increase of grain in the image. If you absolutely feel like you have to develop longer to get a decent image, perhaps you need to increase your exposure time or widen your aperture instead.
Fix the plate with Hypo or Sodium Thiosulfate or, alternatively, with Potassium Cyanide. Beware however that this last chemical is extremely dangerous and every and all precautions should be taken to use this in a safe manner - stay clear if you are a novice as a small amount getting into your system will be enough to kill you. As for myself, I will stick to the less hazardous chemicals.
100 grams Sodium Thiosulfate (crystals)500 ml distilled water
Dissolve sodium thiosulfate crystals completely in water
Measure the time it takes for the plate to clear, and then leave the plate in the fixer for the same amount of time.
Longer fixing times result in loss of contrast.
After this, rinse the plate with ALOT of water. If you are in the field, it might work to bring a sturdy bucket/ bin to leave plates to soak in and give them a proper rinse when you get back to your studio/ home.
Set the plates to dry, keeping your fingers crossed the collodion layer won't just shrivel and peel off in the process...(which means you didn't clean your plate well enough)