rehalogenating bleach - stock shelf life?

[pdeeh]

A few months ago I mixed a stock solution of 200ml rehalogenating bleach using a ratio of 7.5g/l each of Potassium ferricyanide & Potassium bromide. I used deionized water for this.
It worked exactly as desired at the time, using a dilution of 1+10.

It was stored in a dark amber glass bottle at room temperature. I dug it out today and was surprised to find it a dark chocolate colour. Testing it on a scrap negative, it didn't appear to bleach the image at all, even at full strength.

I'd been under the impression that the stock mix would keep well - not indefinitely, but for a year or two.

One faint possibility, I suppose, is that I stored the working strength solution and disposed of the stock last time I used it, although the bottle I opened was clearly marked as stock.

Any comments? Have I simply misunderstood the keeping quality of these bleaches?

 

[Marco Buonocore]

I use a bleach of similar strength (22g ferri, 25g potassium bromide in 1000ml water). I use it full strength, and store it in an amber bottle out of the light. My current batch has lasted more than a year, and in my eyes still performs as intended. I've seen a batch take on a greenish tint, at which point it was tossed. I've never seen a chocolate colour, like you've mentioned. Something is wrong there.

Perhaps the other option you could do is make 10% solutions of both Potassium Bromide and Potassium ferricyanide, then mix the bleach up from that. They may last longer divided.

 

[Ian Grant]

In a good bottle stock solution years from experience, I had 20+ year old bleach that was still fine. it keeps less well when dilute.

Ian

 

[Marco Buonocore]

20 years! Amazing!

I'm interested in comparing the end results from using a fresh bleach to an aged bleach. For example, bleaching back a paper all the way in full strength bleach and redeveloping in sepia toner. Will the old and new bleach produce different colour in the finished print? I'm out of bromide at the moment, but I suppose I'll try it with my relatively young 1 year old batch once I get some more.

 

[pdeeh]

thank you Marco, Ian.

I had thought it should last longer. Perhaps I contaminated it in some way.