Potassium Bromide development restrainer

Potassium Bromide development restrainer

Why does the title of this post sound so technical?

I’ve been making my own B&W film developer from scratch lately because I like being hands-on as well as geeky science stuff 🙂  It produces extremely dense negatives that are gritty and foggy.  I like the artistic effect, but also want to develop clean, “proper” negatives too (like commercial developers give you.)  I did some research and decided to move beyond the basics.  I found that potassium bromide (KBr) acts as a restrainer in B&W film developers.  This helps reduce the development of unexposed silver crystals in the film thus reducing fog and reducing the harsh grain that the formula I am using produces in higher speed films.  By pure luck I found a store that sold some unusual chemicals used in photography and was able to buy potassium bromide!  This is really hard to get in some countries from what I hear.  I was able to buy 500 grams of it for just under 800 yen ($9.50)!

I shot a few still-life shots of some sea shells as a test.  I developed only 1/3rd of the roll in the new KBr formula.  I’ll test the rest of the film in some other variants.

The results are good – much less grain and fog than I was getting.  I shot this with a reverse-mounted Sigma 70-300mm  lens.  My Sigma 70-300mm is complete junk, it actually takes better pictures when put on the camera backwards (using a reversal ring!)  Even then it’s clarity is quite poor, but this was just an experiment and it gave me the magnification I wanted for this particular shot.  .

2 thoughts on “Potassium Bromide development restrainer

  1. hi! can i ask how you figured how many grams of the powder of the potassium bromide should be added to the developer you were using? how did you dilute it, and what not?

    1. I used a recipe found at http://caffenol.blogspot.com/

      I used my own mixing method where I dissolved the coffee in 1/3 of the water, the washing soda (Calcium Carbonate, NOT baking soda which is Calcium Bicarbonate), in 1/3 of the water, and the vitamin C in 1/3 of the water. Then I would mix all three of these together and add 1 gram (which was little more than a pinch) of Potassium Bromide. It worked well for me.

      I suspect that more than the mixing method, the brand of coffee and Vitamine C tablets will affect the results. I lived in Japan at the time and just used what I found at the local grocery store.

      I personally preferred the results without KBr because it gave a really coarse grain and vintage look. But if you are looking for quality KBr gave a look more like a commercial developer.

      I hope this helps.

      -William Milberry

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