Reversal print processing video..new approach

[NedL]

I think you are right if you are talking about dichromate bleaching. In H2O2 bleaching, I think we end up with a combination of the original AgBr which is very light sensitive, and something else that is much less light sensitive. It's quite possible that the 2nd exposure could be enough to make the original AgBr max black before the "other stuff" starts to get tone, or at least much tone. But I haven't seen a pure bright white yet, so maybe I haven't found the right exposure yet or maybe it's impossible. IDK! I haven't finished figuring out the re-exposure yet... I'm still getting some blocked up shadows but the midtones are separating out really nicely. I think contrast control is very important, especially with paper negatives, if we get control, it's a good thing

In my tests, the remaining AgBr keeps its VC qualities ( responds differently to blue and green re-exposure ). I know for sure that the "other stuff" is sensitive all the way down to green, because in some early tests I fogged the highlights with only green light, but I don't know any more than that.

I wonder if there's much "overhead" on paper. What I mean is, in some places there may be more AgBr than is necessary to reach black... if that's true ( I have no idea if it is ) then in your example it might be possible to bring out a little more detail with additional 2nd exposure. With H2O2 I don't think there could be any advantage that way... extra re-exposure will just add tone to the highlights, not bring out detail better than with dichromate. At least that's my guess!

 

[DavidJRobertson]

In the bleaching step it appears that atmospheric oxygen is somehow involved. I had a piece of paper sitting in a H202/CA bleach mixture, with part of it out in free air (though it had been coated with a small amount of the bleach). I was surprised to find that the submerged part had barely bleached at all by the time the part in open air was white.

 

[removed account4]

you guys are blowing my mind

 

[NedL]

In the bleaching step it appears that atmospheric oxygen is somehow involved. I had a piece of paper sitting in a H202/CA bleach mixture, with part of it out in free air (though it had been coated with a small amount of the bleach). I was surprised to find that the submerged part had barely bleached at all by the time the part in open air was white.

Yes absolutely - but only if you add enough CA. I've observed the same thing. If you stick a strip of black developed and washed paper in and let it sit, it will quickly form a pure white strip along the waterline where air is available while the part in the liquid will stay black. If you take it out and let it sit on your desk, it will turn white when it dries as air becomes available. This only happens if there is a large amount of CA. It will bleach a very little at first because there's a little dissolved air, but it will get used up and then proceed only as fast as air is introduced ( faster if agitated ). By the way, this proves that the silver is not dissolved in the liquid but is left on the paper in a "white" form... the one sitting on your desk had the liquid evaporate and no liquid to carry off the silver which is still there. The white silver "salt" that remains is quite light sensitive, but it's not rehalogenated ( or at least it doesn't redevelop into the original image ).

The process Joe and Don and Himself have been using uses less CA and high concentration of H2O2 and is driven more by the the decomposition of the H2O2. I think one of the reasons we're having inconsistent results is that it's a mixture of these two different reactions, and the amount of light sensitivity depends on how much of each reaction takes place. But for sure, if you use a consistent amount of CA:H2O2 and process consistently you get repeatable results with the same amount of light sensitivity each time.

 

[DonF]

I wonder if there's much "overhead" on paper. What I mean is, in some places there may be more AgBr than is necessary to reach black... if that's true ( I have no idea if it is ) then in your example it might be possible to bring out a little more detail with additional 2nd exposure. With H2O2 I don't think there could be any advantage that way... extra re-exposure will just add tone to the highlights, not bring out detail better than with dichromate. At least that's my guess!

My observation is that excess AgBr (meaning development was not to completion) manifests as very dark streaks and mottled patches throughout the highlight areas, both with peroxide and dichromate bleaches. The patches seem to get darker with longer secondary exposure, of course. Perhaps there might be some extra detail in the desired image, but the splotches pretty much make it impractical.

I think the excess AgBr issue is the reason film reversal processing often calls for a silver solvent like hypo in the first developer as a means of controlling contrast. That would make it easier for the development to go to completion without extreme contrast. I have not tried that, though, but it would be worth an experiment. You would need two developer baths, as hypo would not be good to have in the second developer.

Regards,

Don

Dichromate:

Peroxide:

 

[DonF]

you guys are blowing my mind

It's a mind-blowing topic to get your head around! It's fun to formulate and try to test various theories, though.

Don

 

[Joe VanCleave]

Yes absolutely - but only if you add enough CA. I've observed the same thing. If you stick a strip of black developed and washed paper in and let it sit, it will quickly form a pure white strip along the waterline where air is available while the part in the liquid will stay black. If you take it out and let it sit on your desk, it will turn white when it dries as air becomes available. This only happens if there is a large amount of CA. It will bleach a very little at first because there's a little dissolved air, but it will get used up and then proceed only as fast as air is introduced ( faster if agitated ). By the way, this proves that the silver is not dissolved in the liquid but is left on the paper in a "white" form... the one sitting on your desk had the liquid evaporate and no liquid to carry off the silver which is still there. The white silver "salt" that remains is quite light sensitive, but it's not rehalogenated ( or at least it doesn't redevelop into the original image ).

The process Joe and Don and Himself have been using uses less CA and high concentration of H2O2 and is driven more by the the decomposition of the H2O2. I think one of the reasons we're having inconsistent results is that it's a mixture of these two different reactions, and the amount of light sensitivity depends on how much of each reaction takes place. But for sure, if you use a consistent amount of CA:H2O2 and process consistently you get repeatable results with the same amount of light sensitivity each time.

So, as an alternative bleaching idea, hows about just a CA bath, wet the paper then let it sit in the air to oxidize? Maybe dip and repeat if needed? Hmm...

~Joe

 

[DavidJRobertson]

Yeah, I had waaay too much citric acid. Oops.

9% hydrogen peroxide without any citric acid bleached some test strips I had lying about. It seems that citric acid just slows the process (depending on how much is added). Which isn't terribly surprising given that chelating agents are used as stabilizers for hydrogen peroxide.

edit: actually, I use a citric acid stop bath so perhaps a tiny amount got carried over...

 

[DavidJRobertson]

Yes, it does seem to be practical to use 9% hydrogen peroxide without any citric acid at all. It does bubble quite a lot and the bubbles have a tendency to cling to the emulsion, creating a mottled effect as the areas where a bubble of oxygen gas sticks are bleached less. This can be solved by adding a wetting agent. I use tween 20, but I imagine commercial film wetting agents like photo-flo would do the same job. With an appropriate amount of tween 20, the oxygen comes off as a constant stream of extremely fine bubbles, and produces a fine foam on the surface of the liquid.

Having said that, addition of a very tiny amount of citric acid does seem to speed the bleaching itself quite significantly, but reduces the visible bubbling.

 

[NedL]

I think if you wash your test strip really well, maybe needing distilled water ( I've been using RO-filtered water ), you can get it to sit there bubbling away without any bleaching at all. The silver is catalyzing the H2O2 decomposition. If there is even a tiny amount of CA ( like carry over ) it will bleach, just like you said, with unbleached spots under the bubbles. There's a really cool "middle" range of CA, where the bubbles are being made, but then you can see them get sucked back onto the paper and disappear at a new bleach spot -- the O2 in the bubble is being used!.

Joe's idea is the logical extension of more & more CA -- very clever! I have no idea if that would work! Maybe it will work or maybe a tiny amount of H2O2 is needed to do something to the CA and make it possible...

 

[DavidJRobertson]

I was able to get a test strip which had been developed and rinsed in tap water (no citric acid stop bath or anything else) to bleach in H202, albeit slowly.

 

[NedL]

huh. I wondered if tap water has enough chlorine in it to enable bleaching, but I don't have a way to test that. H2O2 and salt will bleach very quickly, but will redevelop to the original image. Also carryover from developer ( bromide ) can do the same... you have to wash pretty well to completely eliminate it from the gelatin. But I don't mean to say you're wrong... I haven't tried anything except 3% H2O2 so I don't know what can happen at higher concentrations.

 

[DavidJRobertson]

I think it must have been something in the developer. My rinsing probably wasn't thorough enough to get rid of all of it. Whatever it was though, it did reverse, sort of. The shadows were black as expected, but the brightest highlights were not even close to white - they were a fairly dark brown. Not a particularly useful result.

 

[DavidJRobertson]

I checked the MSDS for the paper developer I used (Adox neutol eco) - apparently it contains EDTA. That would explain the bleaching.

 

[himself]

the conversation seems to have left me behind a little, so I'm going to have to read back a bit more thoroughly than I have time for at the moment.

but for the moment I just wanted to add to confirm something Don mentions in post #205. I can definitely agree that if the image hasn't developed to completion then the final print will look mottled and uneven in the highlights.

and on that note, I just have a quick question, has anyone noticed that the process seems to exhaust their developer quicker than usual? I realise each sheet gets developed twice, but it seems to need changing more often than usual.

 

[NedL]

I'm falling behind too... I am still meaning to think more carefully about Don's post #205 and haven't had time to do it yet. I think H2O2 ( and also CA! ) will really be bad for developer, so wash very carefully after bleaching and before 2nd development!

I checked the MSDS for the paper developer I used (Adox neutol eco) - apparently it contains EDTA. That would explain the bleaching.

And also there will be bromide ( from the action of the developer on the paper! ).

This is the "standard" that I've been using for testing. It's got varying amounts of blue and green exposure in steps, from no exposure at all in the lower right corner to full max black in the upper left corner. This is what it looks like after the 1st development.

Here's one I made when I was trying to simplify the process. After 1st development, I let it soak in 0.5% CA for 4 minutes and then put it directly into 3% H2O2. ( I skipped washing at all ) I was hoping that the carryover CA would be enough to complete the process, but there was enough carryover of developer into the CA to rehalogenate instead of bleaching to something nonactinic:

( I use replenished developer that probably has a lot of bromide built up in it... I've been using the same bottle for years! )

 

[himself]

I made some fresh developer yesterday and suddenly the gold cast came back. Could this be because of carry over from the newer developer then?

The bleach had also been used quite a bit by then, and seemed to be bleaching quicker and more aggressively. So I then switched back to an older bleach that had been sat in it's bottle for about a week - just to test - and that bleached much slower and the final print didn't have any colour cast.

So a couple of observations, could it be that as the bleach gets used up the CA no longer holds back the peroxide, but once the peroxide (a batch that used to cause yellow discolouring) has broken down enough for the ratio of the 2 to even out it works better again? and does that also mean then that the peroxide can be replenished with more CA?

I'm a bit iffy on the science of all this, but does that make any sense? It's only a theory I have from observing what's happened with my bleach, so I'm happy to be told it's nonsense : )

 

[NedL]

wow, I don't know! There are a lot of "moving parts" that matter. Your fresh developer might also have developed more silver for the H2O2 to work on? It makes sense to me that your bleach will change over time, whether it's driven by CA getting used up or H2O2 decomposing, I don't know!

I made two more photos yesterday and while I was waiting for them to bleach I did two little experiments:

1) straight 20% CA does not bleach, if you let it dry in air.. I have a test sitting on my desk that I've let dry repeatedly, each time putting another drop of CA on it, and there's no indication of bleaching after a day.
2) H2O2 + disodium EDTA does bleach, relatively slowly the way I made it ( 3% H2O2 w/ a couple eyedropper squirts of 2% EDTA )... it bleaches differently: starting in the least dense areas and then working to the most dense. I didn't test if it could be used for reversal -- no idea if it leaves the undeveloped AgBr alone or not. I'll try that eventually....

About 1st development "to completion". Many of the step tests I've done have a point somewhere up in the highlights where the tone is neutral ( but not bright white - it has a little tone ), with the higher highlights having increasing amounts of coppery or gold or cream cast. I don't think it's so much about "to completion" as it's about the maximum density of silver on your negative. If a scene does not have bright white in it, or it does but you don't develop to completion, then the highest highlight will be sort of unpredictable on that scale. So "developing to completion" has the advantage that it puts all the "things that can change" all into the 1st exposure. So from that perspective, it makes it easier to think about or simpler or maybe "more reliable". I don't think that every good print has to have pure bright paper white in it -- but it's common to want that in a print!

I'm using weak pot-ferri and hypo on almost every one of my prints, and the coppery or cream color cast is particularly easy to remove and turn into bright white without affecting the rest of the print much at all. But if the highest highlight ends up neutral, but with more tone than you want, it's much harder to reduce the final print without affecting the deep shadows. So I'm aiming my version of this process to have just a little cream or copper tone in the highest highs.... in other words, if there's a little of that coppery color cast, then I'm thinking of it as a good thing.

 

[himself]

I think "moving parts" is an apt description of the process.

I haven't done any prints for a few days, but I've been wondering if we're all overthinking this slightly (something which is to be expected when you're using a one-off process like this I guess), and but maybe trying to intellectualise ourselves out of a maze that just needs walking through - like for instance, I have (and you have) a working process that more often than not works. Sometimes the odd print of mine comes out with a slight colour cast, but I know that making up some new bleach or developer will solve that problem and I can say "so what" and carry on..

but we can't.

And at the moment I don't have anything constructive to really add, except to say that I'm not sure if it's a highest highlight, but a "highest" highlight - which is to say, I've noticed that I can get a colour cast in what wouldn't normally considered highlights. Oh, I just had a thought - as we've both noticed it's the highlights that start to bleach first (and therefore longest) could it then mean the colour cast is due to these areas being bleached the most/longest/most-aggressive, and would that then mean that if you pulled the same image sooner the highlights might not be copper coloured? or, or if you were to bleach the lightest areas of the negative for the same amount of time, they would be cooper coloured (if your original image was over exposed enough for them to be light enough in the print to show a colour cast)?

 

[NedL]

First of all, yes and I'm probably the most guilty of "overthinking" or "intellectualizing" at the expense of just getting to a practical working process!
I'm a scientist and I can get caught up in exploring how everything works...which is fun and interesting in its own way, but sometimes doesn't make progress toward practical results. ( I spent a lot of hours rehalogenating test strips and seeing what kind of tones they redeveloped into.. which has nothing to do with reversal but really got my curiosity flowing. ) I agree getting to a process that works and is repeatable is the goal, even if we don't understand everything about it!

I haven't done any tests pulling the paper from the bleach before it's all white. But you could be onto something there, and it makes sense. Maybe a set amount of time in the bleach would lead to more consistent results ( and less copper cast? ) than always bleaching to "all white" like I've been doing.

 

[himself]

While I'm not a scientist by profession or schooling, the desire to know exactly how the process is working and worse, the frustration of not knowing why it's not can get overwhelming, but then, if we didn't have that curiosity we'd have all probably given up at the first failure : )

And speaking of failures, I was able to make a couple more prints today with a new batch of bleach, the first 2 images came out with a colour cast while the second 2 came out fine. All 4 were processed the same way and so the only difference could have been the strength of the bleach - assuming the bleach gets weaker each print put through it.

The other, and maybe significant difference was that the first 2 images are a little brighter and the whitest parts are a couple zones higher where the colour cast shows. But this does go a little against what I've observed previously.

A final observation, the first 2 images didn't bleach completely white in 3 minutes, but the only parts that were still visible were midtones but these areas don't show any colour cast on the final print.

Could you give me details of how you're clearing the colour cast again please, I can't seem to find it in the thread. thanks!

 

[NedL]

I'm making a 0.3% solution of potassium ferricyanide:

0.3g pot ferri in 100ml water.

and a weak solution of sodium thiosulfate ( also known as "hypo" ):

~5g hypo in 100ml water.

The hypo is really just 3 "rounded 1/4 teaspoons"..I'm not weighing it and I don't think it matters.

Put the print into the pot ferri for 30 seconds, agitating constantly.
Then put the print into the hypo, where you will see the bleaching take place. It will be done in less than 30 seconds.

This is usually enough to remove the color cast without affecting the rest of the print much at all. If it hasn't gone far enough, just repeat the process and put the print back into the pot ferri for another 30 seconds, then into the hypo again. You can repeat as many times as needed, and it can "open up" the midtones too, but eventually it will start lightening up the shadows if you go too far. It's good to do all this with good lighting so you can see the changes.

When you're done, wash the print again in water then dry as usual.

Once the pot ferri has any hypo in it ( from carryover ), it will start to go off, so I've been making up fresh for each print.

I read somewhere that Alfred Stieglitz would put his prints into weak pot ferri straight out of the fixer. Enough fixer was carried over on the print so that mild reducing could take place and brighten the highlights. I haven't tried that yet with these, but it would be convenient if it worked... just pop the print out of the fixer, into the pot ferri and then wash! I've been meaning to try it!

 

[himself]

that's great thanks!
I just have one possibly stupid questions tho', is there a limit on how long after the fix I can try this, or is now days later ok?

 

[NedL]

I don't think it matters at all. I've got three prints that I processed a few days ago waiting to be reduced. I wet them first with water but have no idea if that's
actually necessary. Have fun! I'm about to go out and make a couple more negatives myself!

 

[himself]

ok great, but just one more : )
is it ok if I've already fixed them?

have fun!!