Shelf life of potassium bromide/iodide
For my final work at artschool I have begun making emulsions, I must say it is like a fresh of breath air to take the reigns (of a horse i do not yet fully understand) and get involved with the formation of light sensitive substances. It is a long road ahead of me and this body of work is just the beginning.
I was so very excited to find an old forgotten cabinet full of misc chemicals, collecting dust with its potential greatly overlooked by the not-so-younger digital generation.
So I have followed Mark Osterman's recipe in the wonderful book of "alternative" processes by Christopher James.
My emulsion seems to be something like ISO 0.15 when developed in dektol 1:1 for 2 minutes. I am wondering whether the dusty old halides are up to the task, I assume they were packaged in the 80's judging by the containers - they are about the same age as me!
I want to make an emulsion that will be appropriate for pinhole photographs so am trying to get as much speed as possible but as I am a novice I am trying to keep things simple.
The silver nitrate is fresh as is the gelatin. I am using a magnetic stirring stove so I've been able to follow the recipe fairly closely, after a pretty messy and pretty much disastrous first attempt, for my second batch I did the precipitation at a rate or roughly 20mls per minute and tried ripening the emulsion at around 60 degrees celsius for 10 minutes, before adding the reserve and then digested it for 15 minutes at 50. furthermore 20 minutes ripening at 60 degrees celsius after I washed it. I was hoping I would end up with something rated between 12 and 25 ISO but alas it definately is not!
Any thoughts would be greatly appreciated.
Last edited by The Stone; 08-27-2014 at 09:55 AM. Click to view previous post history.
I have Potassium Bromide bottled in the 1960's it's fine and the Potassium Iodide I bought in the 80's is OK as well.
Speed is more about the gelatin and how it's sensitised.
We have found that 6 - 12 minutes development in Dektol is best for this emulsion. It should yield about ISO 1 - 2 depending on the chemicals you use and the methods you use for washing.
If your potassium iodide is white, not yellowed I don't see a problem.