Longevity of a Bleach Solution

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

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