BnW reversal attempts

Raghu Kuvempunagar · Apr 18, 2021

YoIaMoNwater said:
What’s the advantage of copper sulphate bleach?

Copper sulphate bleach offers no real advantage over dichromate bleach as it is slow and is a two step process. But it doesn't cause emulsion damage like permanganate bleach and has a good shelf-life and capacity. However, for Adox CMS 20 ii, copper sulphate bleach works better than dichromate bleach due to some idiosyncrasies of the emulsion.

relistan · Apr 19, 2021

Raghu Kuvempunagar said:
Emulsion damage aside, the tint in the slides in the recent video is ugly for my tastes.

YoIaMoNwater said:
What’s the advantage of copper sulphate bleach? Btw the video @relistan posted showed the guy didn’t scan correctly. The video thumbnail of the slide looks more like what it is.

Yeah, the color from the close-ups is from his scanning. If you look while he's holding the slides, they look quite good, none of that weird yellow/brown tint.

AFAIK the good thing about copper sulfate is that it's less problematic than dichromate for your health and the environment, and copper sulfate is easily obtainable, while dichromate is becoming pretty hard to get ahold of in parts of the world for said health/environmental reasons. You do have to use a second bath of ammonia and I think the bleach itself is slower than pemanganate. I am sure Raghu can explain the details better.

Raghu Kuvempunagar · Apr 19, 2021

There's a thread by @Athiril which gives complete details of copper sulphate bleach for reversal processing. I've followed @Athiril's method and found it to be working satisfactorily on a variety of films. My only complaint is it is slow.

YoIaMoNwater · Apr 21, 2021

relistan said:
Yeah, the color from the close-ups is from his scanning. If you look while he's holding the slides, they look quite good, none of that weird yellow/brown tint.

AFAIK the good thing about copper sulfate is that it's less problematic than dichromate for your health and the environment, and copper sulfate is easily obtainable, while dichromate is becoming pretty hard to get ahold of in parts of the world for said health/environmental reasons. You do have to use a second bath of ammonia and I think the bleach itself is slower than pemanganate. I am sure Raghu can explain the details better.

Interesting, I didn't know about that. Potassium permanganate is what I prefer for toxicity reasons and can be made fresh with diluted sulfuric acid.

Raghu Kuvempunagar said:
There's a thread by @Athiril which gives complete details of copper sulphate bleach for reversal processing. I've followed @Athiril's method and found it to be working satisfactorily on a variety of films. My only complaint is it is slow.

I feel like with the already long time for reversal processing, a slow bleach wouldn't be ideal. Thanks for the link though, it's nice to learn something new everyday. So we got permanganate, dichromate, hydrogen peroxide, and now copper sulfate as bleach.

Raghu Kuvempunagar · Apr 22, 2021

YoIaMoNwater said:
I feel like with the already long time for reversal processing, a slow bleach wouldn't be ideal.

Exactly what I also feel. It might be possible to accelerate copper sulphate bleach with a suitable accelerator but I didn't explore that path.

relistan · Apr 22, 2021

@YoIaMoNwater yeah I haven't tried copper sulfate. Only read about it.

Raghu Kuvempunagar said:
Exactly what I also feel. It might be possible to accelerate copper sulphate bleach with a suitable accelerator but I didn't explore that path.

I have half a mind to try it out with citric acid and EDTA... I have a hammer and that sure looks like a nail . Of course EDTA might just bind up with copper and make it even slower.

YoIaMoNwater · Jun 8, 2021

HP5+ @400 with 12 min bleach:

relistan · Jun 21, 2021

I have a little update here. @YoIaMoNwater mailed me a bunch of his films and I did some measurements with my densitometer (X-Rite 331). No H&D curves, but these numbers are looking very good:

Agfa Scala @ 200 — Dmax 2.71, Dmin 0.06
Rollei Retro 400S @ 200 — Dmax 2.92, Dmin 0.03
TMax 100 @ 100 — Dmax 3.63, Dmin 0.16
HP5+ @ 400 — Dmax 2.27, Dmin 0.23
TMax 400 @ 400 — Dmax 2.95, Dmin 0.17

These go along with the previous details he has already posted in this thread for each of those films.

Anon Ymous · Jun 21, 2021

@relistan Are these all 135 films?

relistan · Jun 21, 2021

Anon Ymous said:
@relistan Are these all 135 films?

Yes, and as far as I know they are all the ones he showed earlier in this thread, along with his dev info.

Snowfire · Jun 23, 2021

This thread brings back memories. When I was young, I attempted something like this with paper (not film.) I believe I used dilute nitric acid as a bleach, for what it is worth and it seemed to work. But I never mastered the developer part, and results were a bit muddy. I don't know if HNO3 would work on film, but it is cheap and does not have a lot of gross toxicity.

Donald Qualls · Jun 23, 2021

Well, silver nitrate is soluble, so if the NHO3 actually reacts with the image silver, the result should dissolve. Beyond that, it should not react with the insoluble halides in the undeveloped parts of the emulsion. The main bad news is it's hazardous to handle (though the hazard is more immediate than potassium dichromate), and not terrifically easy for ordinary folks to obtain (these days, however, you can probably buy it from Amazon sellers). Buying nitric acid is likely to get you on a "list" (because it's so useful for making explosives) but if you have no criminal record it shouldn't be a big problem.

I'd be cautious using nitric acid on fiber paper, however -- there were those incidents in San Francisco back in the 1840s where people's collars caught fire after being whitened with nitric acid at the laundry...

Raghu Kuvempunagar · Jun 23, 2021

@Snowfire: I guess your Nitric Acid bleach probably also had Potassium Permanganate in it. Are you sure it had only Nitric Acid?

Snowfire · Jun 23, 2021

Raghu Kuvempunagar said:
@Snowfire: I guess your Nitric Acid bleach probably also had Potassium Permanganate in it. Are you sure it had only Nitric Acid?

No, at the time I did not even know that KMnO4 would work. It was literally just dilute nitric acid. And as diluted as it was (about 1M as I recall,) it wasn't that bad to handle--not like the concentrated acid. You wouldn't have wanted to go out of your way to put it on your skin, but if you accidentally got a bit on yourself, as long as you rinsed it off promptly there were no dire consequences. It is possible that even more dilute solutions might have worked--I did not investigate that..

I also discovered that if you mixed it with some hydrochloric acid (aqua regia,) it behaved as an antideveloper: you could put a print in it out of the developer and it would actually erase the image (sort of) and return the paper to an unexposed, photosensitive state. Why I thought this was a good idea, who knows; nothing really useful came out of those experiments.

Donald Qualls · Jun 24, 2021

Yep, with chloride ion it'll rehalogenate (though most enlarging papers are mostly bromide, chloride is really slow and normally used for specialty contact printing papers like Azo and Lodima). I think the halide created is in an exposed state, though.

I checked, Amazon sellers almost don't list nitric acid at all, there was only one listing and it was "out of stock". That means having to find it from chemical suppliers, who are often reluctant to deal with the public.

Snowfire · Jun 24, 2021

Donald Qualls said:
.
I checked, Amazon sellers almost don't list nitric acid at all, there was only one listing and it was "out of stock". That means having to find it from chemical suppliers, who are often reluctant to deal with the public.

Ah, the paranoid times we live in. Back in the 1970s, society was more innocent and less terror-centric than it has become lately. I remember my high-school teacher demonstrating a nitration reaction with nitric/sulfuric acid and it was just another demonstration to us.

If you really want nitric acid, it can be synthesized by bubbling NO2 through water or by various metathesis reactions such as phosphoric acid/copper nitrate (and I wonder if copper nitrate would have any value by itself as a bleach?)

Raghu Kuvempunagar · Jun 24, 2021

Snowfire said:
No, at the time I did not even know that KMnO4 would work. It was literally just dilute nitric acid.

Oh Ok! I asked because Haist describes a Permanganate + Sulphuric Acid reducer in his book and says that Sulphuric Acid can be replaced by Nitric Acid. There's no mention of a Nitric Acid only reducer/bleach in the book. But if it worked for you, why not.

Donald Qualls · Jun 24, 2021

The way most "home users" get nitration solution these days is by mixing stump remover with sulfuric acid drain cleaner. Yep, get it all a Home Depot. Unfortunately, that produces a mixed acid (as far as I know), so probably not very helpful for our needs. Nile Red on YouTube would probably distill the sulfuric first, recrystallize the stump remover to "clean" it, and use an excess of it to push the equilibrium toward nitric acid -- and then come up with a way to separate them.

For my darkroom, if I can't buy it in a correctly marked bottle, I don't think I want to mess with it.

Anon Ymous · Jun 24, 2021

@Donald Qualls There's also the possibility to acquire nitric acid from agricultural supplies stores. Not available from any of these stores, but some may stock it, among other fertigation supplies.

Donald Qualls · Jun 24, 2021

That's worth checking. We don't need high concentration, after all...

Snowfire · Jun 24, 2021

Evidently the mining hobbyist community uses it, too:
https://www.walmart.com/ip/10-Liter...ning-Metal-Recovery-Platinum-Silver/378055868

Donald Qualls · Jun 25, 2021

Since the rule I recall from Chem 101 (1978) was that nearly all nitrates are soluble, this makes good sense for recovering the last traces of metals like gold, silver, and platinum from ore (though you need to add hydrochloric to get a reaction with gold and have to heat the resulting aqua regia for platinum).

Of course, if I have to get it from Walmart, it may as well not exist...

I'm rather surprised, however, to see Walmart offering 67.2% strength on their web site, but Amazon not having it at all, in any strength.

YoIaMoNwater · Jul 10, 2021

Fomapan 400 @ 400: I tried reversing this film with both the leader strip and the whole roll. Bleach cleared the leader strip at 11 min but I extended to 15 min for the whole roll. This was a terrible mistake because after putting in the 2nd developer for a few min, I could see black pieces of emulsion floating around the developing tank. Next trial with this film probably need to limit bleaching to 11 min or less. Contrast seems fine; however, there's a noticeable reduction to Dmax as the blacks are not black.

TMax 100 @ 100: I also attempted this film again but this time bleached for only 5 min. Previous attempt for TMax 100 also resulted in emulsion damage when it was bleached for 8 min. I have to say that although the densitometer readings for Dmax and Dmin look good, this film does not reverse well in my process. Unless you're shooting contrasty scenes, the reversed film will look quite flat. One thing to note is that for the bleach step, I normally agitate continuously for 1 min then 10 s for every 30; however, I think if I had continuously agitated for the entire 5 min then the result wouldn't be as dark. If anyone else want to try to optimize this, feel free to go ahead.

Raghu Kuvempunagar · Jul 10, 2021

YoIaMoNwater said:
although the densitometer readings for Dmax and Dmin look good, this film does not reverse well in my process. Unless you're shooting contrasty scenes, the reversed film will look quite flat.

Where exactly in the film strip did you take a reading for DMax and DMin? Can you mark those points on the film strip?

YoIaMoNwater · Jul 10, 2021

Raghu Kuvempunagar said:
Where exactly in the film strip did you take a reading for DMax and DMin? Can you mark those points on the film strip?

You'll have to ask @relistan about it as he did the readings.

BnW reversal attempts

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