a new chapter of Caffenol development is ready to be published. I was not satisfied with Caffenol/C and high speed films and I didn't recommend it. Too much fog, flat in contrast, poor usable speed, ugly grain. but I constantly thought of trying to modify Caffenol-C-M for these films. Potassium bromide (KBr) is well known as an anti-fogging agent, but I thought it would mess up the concept of great shadow rendering. I was wrong. So good and bad news: KBr works well with Caffenol, but it is not available in regular supermarkets. In Germany a pharmacy in my neighborhood was able to deliver it within a couple of hours, 100 gramms for 15 Eur. Quite expensive compared to the other ingredients, but it will be good for 100 litres of developer and some hundred films. So the additional coast will be about 4 - 8 Euro-Cent per development. Potassium bromide is not toxic and doesn't spoil the environmental friendly coffee soup.I don't know how easy potassium bromide is available in other countries, reports are welcome. The german name is Kaliumbromid, or you may ask for the scientific latin name "kalium bromatum" in pharmacies.
How to: I made a stock solution of 10 gramms KBr in 300 ml destilled water, stored in a glass bottle. It will last almost forever. 1 ml contains 0,033 gramms KBr. 250 ml developer need 7.6 or easier 8 ml of the stock solution. This equals 1 gramm per litre KBr. Simply add the 8 ml to the ready mixed 250 ml Caffenol-C-M and voila: Caffenol-C-H. Be sure to do the math right! I'm sorry.
Edit: if still too much fog, use 2 g/l of potassium bromide.
So far I used HP5+ and Neopan1600, both with excellent results. 1gram per liter KBr was added to the Caffenol-C-M recipe, no other changes. Developing time was 15 minutes like before, or 30 minutes stand development with agitation first 30 seconds and 3 minutes presoak in tap water.
Thank you very much Caro and Chris for allowing me to publish the images. Finally an example of the Acros100 in Caffenol-C-H, also works perfectly. But for 100 ASA films I still recommend the simple Caffenol-C-M because the KBr isn't really needed.
Best regards - Reinhold