Longevity of a Bleach Solution

[StevenPituch]

Hi All,
I am in the midst of doing some tests of David Kachel's SLIMT method of contrast reduction for film. I am using a working stock solution of 10 gm of potassium ferricyanide and 3.3 gm of potassium bromide in distilled water to make 1000 ml. I take 10 to 20 ml of this working stock solution to make the bleaching solution that I use when I develop film. I was just wondering how long this working stock solution will keep in a partially filled brown glass bottle in darkness at room temperature. I just don't want to chance ruining a film with a bad solution.
Sincerely,
Steve Pituch

 

[Doremus Scudder]

Steve,

I've been using SLIMT techniques for negative contractions for years. I always make up two stock solutions, a "Solution A," which is a 10% potassium ferricyanide solution and a "Solution B," which is ~3.3% potassium bromide. These solutions last for years; I made a liter of each up about five years ago and I'm still using them. To use, I mix equal parts of A and B, which gives the same ration as you seem to be using.

I've never made up a stock solution with both ingredients, so I'm not sure how long it would last. I think it would be good as long as there were no color change.

My working solution dilutions range from 0.005% to 0.04% of the ferricyanide (the bromide content is 1/3 of this, of course); times for the SLIMT bath range from 2-4 minutes.

I use small syringes to measure out the volumes as follows:

2ml A:2ml B per 500ml = 0.04% ferricyanide
1ml A:1ml B per 500ml = 0.02%
0.5ml A:0.5ml B per 500ml = 0.01%
0.5ml A:0.5ml B per 1000ml = 0.005%

The nice thing about having stock solutions of single chemicals is that I can use them in different proportions for different purposes. The ferricyanide and bromide get mixed in a stronger solution for print bleaching, I use the bromide as a print developer additive at times too. I've got BTZ, sodium carbonate and a few other chemicals in readily-available stock solutions as well.

Hope this helps,

Doremus

 

[StevenPituch]

Thanks so much, Doremus,
It looks like my potassium ferricyanide dilution where I got nice results so far is .02% but with longer bleach time than you. This is very encouraging news. I still need to digest all your information, but will likely make my working solution directly from the stock solutions in the future.
I am attaching a preliminary plot.

Sincerely,
Steve