Do as you oughta, add acid to watta.

It can also boil if water is added to acid, since the dissociation can be highly exothermic. I'm not a chemist (physicist by training) but I would stay away from potassium dichromate unless you are comfortable with handling chemicals, it is acutely toxic, carcinogenic, and reproductively toxic whereas the main danger from sulphuric acid is acid burns and burning (which is moderately unlikely), it is apparently also carcinogenic (but I believe less so). Ilford suggests "For solution B add 10ml of concentrated sulphuric acid to 490ml water. You can use a 10% solution of diluted sulphuric acid if you can't find it concentrated. In this case, add 100ml to 400ml of water to make the part B bleach solution." I would consider 10% sulphuric acid to not be very dangerous. Don't drink it, don't get it in your eyes, but if you get it on your skin you can wash it off with water and will probably not have any real damage (other than some pain, irritation, discolouration). 10% sulphuric acid can be handled by children in school. I would still wear sensible PPE, eyewear, gloves, apron or better a lab coat, whatever the msds says. If you get it on your clothes, take them off as soon as practical. If you get it on your skin wash it off as soon as practical. Only operate near either water than you can run (a tap) or a large amount of standing water that is not contaminated with other chemicals, so you can wash yourself off if needed. The 1% solution that you'd actually use for the chemistry I would consider to be basically safe. Don't drink it, don't put your hands in it, wash it off if it gets on you, but don't panic. Make the dilution, put away the concentrated chemicals, and then work with the dilution. Carefully label everything so you know how concentrated everything is, labels like 'ACID' are useless. Labels like '1% dilution of sulphuric acid - mildly corrosive, don't get in eyes' and '10% dilution of sulphuric acid - corrosive, don't get in eyes or skin - wear goggles' is more useful.

Klaus, thank you. My fixation on chemical safety has something to do with my professional life.

Thank you for the reminder about lab safety.

Did you try it? And if so, was it successful?

@@g-r-a-e-m-e- Haven't tried it yet.

@@utekopka7920 Ok thanks for replying 🙂. I am definitely interested too.

I've thought about it for certain, could be an inexpensive source of negatives for contact prints.

I haven't used this process with film, but using the same concentrations is a good starting point. You may want to refer to the APUG discussion thread on the topic, perhaps others there with more experience can provide guidance. Link: www.photrio.com/forum/threads/reversal-print-processing-video-new-approach.153447/ Regarding the fixing after the second development, you may be right about that, but I figured it's best to be safe and fix out whatever remaining silver halides might be present.

There's probably some gas given off, maybe hydrogen? Not certain what kind. A daylight tank is vented, so just use it in a well-ventilated space and it should be fine. As I remember, the lower concentrations had issues with mottling and it took a lot longer to do the reversal. But this process demands experimentation. Good luck.

Thank you for your insight. Keep us informed of your results.

The traditional reversal process using chromate bleaches were used to make b/w slides, so yes, this should work also with film.

Mike B. of "A Year of Film" blog used a similar process on regular BW film and some Kodahrome (no color)

I don't yet have a gram scale, so this is as precise as I can get right now.

Joe Van Cleave any way to private message me your details (mailing address or PayPal)? I'll order one for you or send you the funds to do so.

I have the money, just haven't gotten around to ordering one!

Joe Van Cleave I'm not saying that you don't have the funds so I apologise if it sounded that way and I meant no offense, just wanted to help support the channel and the work that you do.

I appreciate your support! Thank you. I do understand it would be more helpful for viewers, who want to delve into this, to have dry measurements in units of weight instead of volume. I'll work on this!

With proper exposure and development the negative should appear very dark, prior to bleaching white. I recommend you try non-caffeine-based developers that are more chemically active.

Yes, the paper is not red sensitive, you can load it under safe lights. It's ISO (or exposure index) varies, depending on the amount of blue/UV light in the scene, but my experience suggests it varies from ISO2 to around ISO4-6.

@@Joe_VanCleave thanks!

Neat idea.

develop>fix>bleach>paint emulsion side black. should end up with something similar to wet plate or tintype.

Vanish could be a good starter of the chemical process together with the H2O2, like in Retrobright.

I'd recommend making test strips to determine the optimal exposure time, just like you'd do when printing a negative.

@@Joe_VanCleave thank you for the reply! I should clarify that I meant moreso the developing times in the various chemicals and re-exposure. For example, would it be reasonable for me to assume double the time in bleach vs the rc paper? I would also imagine that time's affect for re-exposure would remain constant and not change between the various papers. I just want to make sure there's nothing I would have forgotten to account for.

I haven't had the process work with 3% peroxide, hence why I use stronger.

Joe Van Cleave I tried an 18% solution just as you described but some of the dark areas from the first Dev never bleached out all the way. Is this normal? After 5 minutes(I dumped and used new bleach a few times) these parts were still grayish and I just decided to turn the lights on, fog it, then develop anyway. This resulted in a pretty dark overall image with a few highlights. My solutions were to take a less contrasty picture and maybe to use a stronger solution for the bleaching agent(20%+). Any tips?

@@JRichardctr I will do up to 4 or 5 passes through the peroxide and acid to ensure good bleaching.

If the paper goes completely white in the peroxide then the bleaching is adequate, otherwise keep it longer in the citric acid and peroxide. Also make sure you use a fully saturated citric acid solution, meaning excess undissolved powder is okay. If it goes black in the second developer it sounds like the initial exposure in-camera was too little. That initial exposure should use on average about half of the halides in the emulsion, which then get etched away in the peroxide, leaving about a similar amount of halides to form the positive image after re-exposure and the second developer. Too dark of a final print means too many unexposed halides were left in the emulsion after the first exposure and bleaching. This is assuming the second, flashing exposure is uncontrolled in intensity and duration, like we’ve been doing, and hence exposes all of the remaining halides in the paper. It could be that fiber paper has more silver than RC, so you need more initial exposure, and also more bleaching to clear it to white. Another strategy would be to control the second exposure intensity and time, instead of merely fogging the paper with an uncontrolled amount of light, treating it like a darkroom print exposure, then develop for a good positive image, then stop and fix out the remaining silver halides. I personally like using RC paper for this process because it permits making prints in the field, on the street, where you don’t have time for archival washing that fiber paper requires. But for studio work I can see the appeal. Good luck!

@@Joe_VanCleave Thank you for your quick reply! I'm going to try some more careful exposures, I've been doing these at ISO 3-4, which I normally do for paper neg on RC paper. I see a lot of the resources are saying around 1.5 ISO so I will try that. This would make sense of the prints going black in the second developer, but any way to explain why they don't bleach out in the H.P.? I've left it in about 10 min at most and barely see any black bleach out.

@@ianlewandowski352 As I said earlier, make sure the citric acid is strong. Go a full 3-4 minutes in the acid before the peroxide. And go straight from citric acid to peroxide, don’t rinse the paper in between. I’ve also seen where under exposed images don’t bleach as well as properly exposed.

@@Joe_VanCleave Sorry, I'm confused, there's a solution of only citric acid before the peroxide + citric acid solution? So far I've just been developing, rinsing, then bleaching.

@@ianlewandowski352 Yes, the citric acid after the developer acts as a stop bath and also prepares the developed metallic silver to be etched by the peroxide. Make a strong solution of citric acid from powder, enough so extra powder won’t dissolve in the tray, and you know it’s strong enough. 3-4 minutes in the citric acid, then directly into the peroxide. The print should start fizzing and immediately begin to turn white.

Not yet! I'll find out today or tomorrow, when I attempt to reuse that brown glass bottle of bleaching agent.

Any update on this?

Short. When just stored hydrogen peroxide is not stable and it easily decomposes into oxygen and regular water. Keep it in tight closed squeezed plastic bottle without air inside (only liquid). When used for bleaching hydrogen peroxide is being reduced actively during the washing - this is how it works. The weaker solution you use - the shorter life it has (or even it may be not sufficient to do job at all).

I have not yet, mainly because Harman Direct Positive Paper is fiber-based and the process is faster and more convenient, using conventional chemistry. But I have little doubt this process would also work with fiber paper.

Reduced to elemental silver, which then naturally oxidizes.