Great stuff, Ed and Niranjan. That all makes perfect sense.
I was thinking of trying some phosphoric acid (I have some 35% on hand for making acid phosphate old fashioned beverage "phosphate soda" additive) to replace the citric. I read that the acid in a non-halogenating simple bleach needs to be non-organic, which rules out acetic acid, but phosphoric is a mineral acid, like sulfuric. Would the reduction reaction with phosphoric acid form a fixable or washable silver compound?
Best,
Don
just a quick update, I've been working on the portraits I had initially hoped to use this process for and despite some early success my attempts seem to have slipped back to the grey/blacks of my initial tests.
My process is the same as when successful except that I had to mix new bleach (and variable first exposure) and since then they've been a bit hit and miss. I realise the 2 spoons of citric acid is hardly a definitive measure and there must be some slight difference in each batch of bleach, but the image is still bleaching to completely white in about 3 minutes.
And but despite this, 3 of the 5 images I developed today where grey/white and show a lot of mottling.
So now I have a series of stupid questions, and if anyone has any ideas..
How would over/underexposing the initial exposure effect the final image?
Can bleaching be incomplete, even if the paper is like totally white?
Does initial exposure effect how much 2nd exposure you need?
And finally, should the second exposure be the same no matter what, and the final effect will look over/underexposed like a normal neg/print?
thanks, and I've been following along with general discussion - lots of interesting information!
Dafydd
So I just had the opportunity to take and process another image, and I think it illustrates well what I mentioned in my previous post ref the first exposure.
The first image, which is grey and black (and no whites) looks to be the better exposed, maybe just a little over, however the second image is the one with white highlights*.
Both were processed in the same bleach to completely white and re-exposed for 2 minutes with the enlarger.
Unfortunately I'm unable to scan them at the moment, so had to snap them with my digital camera, but I think the difference is visible.
View attachment 188674 View attachment 188675
*it looks a little more white in person, especially the lettering, but the lighting has added a little bit of a yellow cast
Joe & Don,
A little extra info, I'm rating the paper at iso 1.5, and metering the same way as always. Unfortunately, the light is a little variable because I'm using natural light.
So that's what I was initially thinking too, but looking at the prints today, now dry, the 2 worst (as in most grey) look to be exposed better that the one that could have been said to have worked. There's much better detail in the shadows and overall it looks fine, except that the highlights are grey (looks like a ambrotype again) and not white.
Could it be that overexposing on the first exposure leads to grey highlights? or that overexposing the first exposure and then under/overexposing the second makes it grey?
And just to comment on volumes, I think you're under using your bleach Joe. I'm using 300ml (12%) with 2 tsps and after 5 8x10 prints yesterday they're still bleaching to completely white in 3 minutes.
I think the first has a good in-camera exposure, but was overexposed some during the second exposure. Try 1 minute. Highlights (background) look dark.
The second seems slightly underexposed in-camera and also overexposed on second exposure.
Just my impression based upon my own trials....
Don
I think there is more going on than we are accounting for
Something is not quite right about our thinking. In my opinion we've made a model of how this process works that is too simple. I think there is more going on than we are accounting for. ( I mean the H2O2 process.. I think the dichromate process IS more like the simple model ).
In the 2nd exposure, if all the remaining silver halides are exposed, how is it that:
* joe gets different results by using a limited re-exposure than processing in full room light
* I get VC contrast control in my second exposure
* Don says an overexposed negative can be compensated for by increasing the 2nd exposure
All of these things argue that there is still some "wiggle room" with unexposed halides during the 2nd exposure. Otherwise, the end result would be completely determined after the bleach step, but none of us are finding that to be true.
I don't think I understand the process well enough to answer Dafydd's questions yet... but they're good questions
there must be a lot of "wiggle room" at each stage of the process, otherwise how could we all be having different problems at/or from different stages?
obviously there isn't uniformity across all our processes, but the variety of results seems to suggest that not only is there possible variation at each stage, but that also the previous stage influences (and introduces new variations) the next stage so much that there can't be a standard correct - exposure = Y bleach dilution = X re-exposure - for the process.
and so, if this is the case, could it be that the number of variables is too large to really get a handle on, and that we're just chasing ourselves in circles until we have a large enough sample size to have exhausted all possible combinations (if that's possible)?
I wonder if you do experimentation first in the darkroom with the use of a step wedge, like that made by Stouffer
Don, is the paper wet during the second exposure? Has the front and/or back sides been superficially dried via squeegee? Just curious.
I did not squeegee, but I see what your getting at! I have softened water, so it sheeted off pretty well after the post-bleach rinse. These are probably the worst results I have gotten. Wildly uneven bleaching!
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