Large format direct positives B&W

[koraks]

Yeah, I agree and see your point. I'd approach it in a similar way. I could have moved all my negative intensification to permanganate instead of dichromate by now. But given the minimal amount of dichromate involved on a yearly basis, and the fact that it's discharged in the form of plain old Cr(III)...

 

[P C Headland]

Photo Engineer felt that dichromates were safer than permanganate. He felt that the risks of dichromates were easily mitigated while he worried about how strong an oxidizer permanganate is. He was also very worried about accidental combinations with other common darkroom materials. He didn’t mind having dichromate in his house but said he wouldn’t have permanganate in it.

Safety is a difficult thing to quantify. Clearly all three of the chemicals being discussed need to be handled with care. I haven’t tried B&W reversal processing myself but I am interested. Reading the different discussions here makes it seem like good results are certainly possible but it does take quite a bit of testing to nail the process as compared to negative development. If (when?) I try my hand at it I will most likely do it with the hydrogen peroxide/EDTA bleach that has been discussed.

A Better Black and White Reversal Bleach with Hydrogen Peroxide

In a previous post, I described how to develop your own black and white slides using a simple bleach based on hydrogen peroxide and vinegar. This post is about an improved bleach that has a number of advantages over that one. There are a lot of patents out there from the 1970s through the late...

imager.ie

If I couldn‘t get that to work I’d just go the dichromate route with a reducing agent like citric acid to least make the waste less toxic.

I've tried a few times using hydrogen peroxide with 35mm and 9x12cm sheet film, the results were quite positive (...) I started down that track having watched some 8mm movie film home processing videos, very similar to what is described here: https://imager.ie/black-and-white-reversal-with-hydrogen-peroxide.

The last roll I tried:
35mm Fomapan 100 at 100
1. Develop in PC-TEA 1+30 @25c for 12 minutes
2. Bleach for 20 minutes @30c
3. Re-expose to light (bright bulb) 2-3 minutes
4. Re-develop PC-TEA 1+30 @25c for 12 minutes
5. Rinse

Bleach: 250ml Hydrogen Peroxide 3% + 15ml White Vinegar

 

[tykos]

I looked at Adox's B&W reversal kit information, and it seems not containing any of the above hazardous chemicals in its bleach. Just curious if Adox has a secret formula that is much safer?

in the SDS there's permanganate and some hazard pictograms https://www.fotoimpex.com/shop/images/products/media/66896_4_MSDS_EN.pdf

 

[Donald Qualls]

in the SDS there's permanganate

Most or all of the European reversal kits have gone to permanganate because of a near-complete ban on hexavalent chromium in the EU. NOT because it's a better or (for this purpose) safer chemical, necessariy, but it has less environmental effects.

 

[blee1996]

I've tried a few times using hydrogen peroxide with 35mm and 9x12cm sheet film, the results were quite positive (...) I started down that track having watched some 8mm movie film home processing videos, very similar to what is described here: https://imager.ie/black-and-white-reversal-with-hydrogen-peroxide.

The last roll I tried:
35mm Fomapan 100 at 100
1. Develop in PC-TEA 1+30 @25c for 12 minutes
2. Bleach for 20 minutes @30c
3. Re-expose to light (bright bulb) 2-3 minutes
4. Re-develop PC-TEA 1+30 @25c for 12 minutes
5. Rinse

Bleach: 250ml Hydrogen Peroxide 3% + 15ml White Vinegar

Hi, Thank you for sharing the recipe. I do have Hydrogen Peroxide 3% at home for lens fungus removal.

One more question: have you tried any other developers? Thanks!

 

[P C Headland]

Hi, Thank you for sharing the recipe. I do have Hydrogen Peroxide 3% at home for lens fungus removal.

One more question: have you tried any other developers? Thanks!

I also tried Rollei Retro 400s (135) at EI200:
1. Develop in Rodinal 1+25 @23c for 15 minutes
2. Rinse / soak 10 minutes at 25c
3. Bleach @30c for 15 minutes
4. Re-expose 2-3 minutes
5. Re-develop in Rodinal 1+25 15 minutes
6. Rinse

After the first development, I rinsed the film in 25C water before the bleach at 30C, just to help avoid any temperature shocks.

Also, 9x12cm Classic Pan 200, developed in Rodinal 1+20 for 10 minutes, then 20 minutes bleach, re-exposure then 10 minutes in the second Rodinal 1+20 developer. Same temperatures as above.

I prefered the results I got with PC-TEA, but that may have been due to that being the third attempt.

Let us know how you get on.

 

[blee1996]

I also tried Rollei Retro 400s (135) at EI200:
1. Develop in Rodinal 1+25 @23c for 15 minutes
2. Rinse / soak 10 minutes at 25c
3. Bleach @30c for 15 minutes
4. Re-expose 2-3 minutes
5. Re-develop in Rodinal 1+25 15 minutes
6. Rinse

After the first development, I rinsed the film in 25C water before the bleach at 30C, just to help avoid any temperature shocks.

Also, 9x12cm Classic Pan 200, developed in Rodinal 1+20 for 10 minutes, then 20 minutes bleach, re-exposure then 10 minutes in the second Rodinal 1+20 developer. Same temperatures as above.

I prefered the results I got with PC-TEA, but that may have been due to that being the third attempt.

Let us know how you get on.

Thank you again! I have a roll of Rollei 80s that could be used for such experiments.

 

[YoIaMoNwater]

Thank you again! I have a roll of Rollei 80s that could be used for such experiments.

I've gotten very good results with 1:6 rodinal as first developer for Rollei Retro 80s and Superpan 200/Retro 400S: https://www.photrio.com/forum/threads/bnw-reversal-attempts.179724/post-2386335

1. 1:6 rodinal 15 min
2. wash 3x
3. permanganate bleach (0.12% w/v KMnO4 in 2% sulfuric acid) 8 min
4. wash 3x
5. sodium metabisulfite clear (0.4% w/v) 2 min
6. wash 3x
7. re-exposure under 100W tungsten lamp 1.5 min/side under water in a white bowl
8. 1:6 HC-110 15 min
9. wash 3x
10. fixer/hardener 5 min
11. wash 8x
12. dry

 

[George Collier]

Thanks for all the replies - you've given my friend a good starting point.