using just potassium ferricyanide as a bleach for reversal images

[removed account4]

i have read plenty of recipes about reversal images from photo paper.
i have an aversion to using sufuric acid though. i do have some potassium ferricyanide
that i use for making cyanotypes ... is it possible to do the bleaching step with that, instead of battery acid?

i know one is probably just as bad as the other, but i have ferri on hand ...

thanks for your suggestions and advice !
john

 

[pdeeh]

you can't use only ferri as a reversal bleach.
the actual chemistry is beyond me to explain
(perhaps Gerald or PE will chip in)

There are formulae using Sodium bisulfate instead of Sulfuric acid - perhaps a bit less worrysome to handle for you?

 

[removed account4]

you can't use only ferri as a reversal bleach.
the actual chemistry is beyond me to explain
(perhaps Gerald or PE will chip in)

There are formulae using Sodium bisulfate instead of Sulfuric acid - perhaps a bit less worrysome to handle for you?

thanks pdeeh !

yeah i was just trying to use what i had on hand .. looks like i will be waiting a while before
attempting reversal fun that way .. unless i can do it with cream, sugar and coffee

- john

 

[Athiril]

Strong mineral acids cause potassium ferricyanide to release deadly hydrogen cyanide gas. You know the acid to in the bleach to help form soluble silver sulphate. Although iirc, ECN-2 uses diluted sulphuric acid to adjust pH of the ferricyanide based bleach, so perhaps diluted sulphuric acid is fine.


You can always make up a stock solution of weak sulphuric acid for easy handling for bleach making. You could also use sodium bisulphate.

 

[Photo Engineer]

Look guys, the reversal B&W bleach relies on forming Silver Sulfate from the NEGATIVE Silver image. This dissolves in the bleach leaving POSITIVE Silver halide. The second developer develops the positive image.

This keeps coming up over and over. The chemistry of bleaching B&W and color is totally different and it is only sometimes that the bleaches can be crossed over. But that is another story.

PE

 

[Gerald C Koch]

When I was doing lab work and working with concentrated acids I learned three things.

o When you get concentrated nitric acid on your skin you will not know until the next day when you notice a new yellow callous on your skin.

o When you get concentrated sulfuric acid on your skin the oil on it protects you while you walk to the sink to wash it off. However any clothes will not be so lucky and will become rags.

o When you get concentrated hydrochloric acid on your skin it starts to painfully bite immediately and you run to the sink to wash it off.

In a dichromate or permanganate bleach sodium bisulfate is a safe alternative to sulfuric acid.