Color cast problem with DIY color negative chemistry

koraks · Mar 11, 2025

lamerko said:
Since you are doing a "DSLR scan", you need to lock in the camera settings - color balance (neutral profile), ISO, aperture, speed.

That, and chuck NLP out of the window.

originalwinslow · Mar 11, 2025

koraks said:
That, and chuck NLP out of the window.

Do you think that NLP is in general an inaccurate conversion tool? I have had some weird experiences that left me confused over the years but it's effective for streamlining the whole process. I get MOSTLY consistent results, and after probably 20,000 conversions I've certainly put it through its paces.

Most seem to agree that NLP is the best conversion software. Overall I've been satisfied. I have yet to try the new Smartconvert program but seems like it has less tools.

What is your workflow?

koraks · Mar 11, 2025

originalwinslow said:
Do you think that NLP is in general an inaccurate conversion tool?

Inaccurate: yes, very much so. But accuracy is in general not necessarily the best criterion for usefulness. So by all means, use it. But when it comes to trying to figure out how different test negatives relate to each other in a more objective way, NLP is a liability and should be avoided.

originalwinslow said:
What is your workflow?

Flipping the movie – Color negative inversion process video – Koraks tinkers

tinker.koraks.nl

To each their own, though.

Please note that my comment about ditching NLP is really limited to the technical troubleshooting of negatives. I imagine it works well for getting pleasing images in your normal workflow.

originalwinslow · Mar 11, 2025

Each layer of this discussion seems to uncover further points of inaccuracy in my process. Thanks for helping me hone it in. I'm working towards getting everything as accurate as possible while maintaining speed and efficiency.

I just took a brief look at your video and wow yes I do see how that workflow is likely much more accurate than the automatic conversion via NLP. I will give it a shot one of these days. I have never used GIMP so there will be a learning curve.

I've been playing a bit with those test images. Sometimes NLP needs some coaxing to get it where it needs to go. It's certainly an estimation rather than a 1:1 representation. The bleach bypass looks much cleaner and I don't know why. I'm seeing a lot of digital (?) noise in the regular dev conversion.

One thing at a time, though.

koraks · Mar 12, 2025

originalwinslow said:
The bleach bypass looks much cleaner and I don't know why. I'm seeing a lot of digital (?) noise in the regular dev conversion.

Rescan and invert manually as I've shown; I think things will become a little easier to interpret at that point. The images may not be as pleasing as the NLP-converted ones you've got so far, but it'll help you better understand the differences, and ultimately the processing problems you're running into - which still puzzle me, btw.

lamerko · Mar 12, 2025

I have a really smeared film during processing - I never understood how it happened. Strange blue casts and... noise. No retained silver.
What you think of as digital noise may not be digital noise at all - it is likely to be artifacts of the film itself. Set the camera to ISO 100 - the slightly longer shutter speeds of this camera will not reproduce visible noise. Also, in the new versions of Lightroom and Photoshop there is an integrated algorithm for cleaning noise before RAW conversion - this has nothing to do with smearing artifacts - a very powerful tool. However, it will only work on the actual digital noise, not on the captured artifacts from the film itself.

originalwinslow · Mar 15, 2025

Occam's razor - the simplest solution is usually the correct one.

After developing 18 rolls yesterday (12 c-41, 6 ECN-2) I can conclude that the issue with developer/bleach crossover causing staining to be entirely resolved. At least as far as I can perceive it.

The culprit? Probably just insufficient washing. The only variable I changed yesterday was to add a 5th wash cycle after developer/bleach and up the stop bath to 250ml 5% white vinegar/750 water (1.25%).

There may have been a chemical issue also at play here, but I think that the most simple answer is likely the correct one.

Just wash more!!!

I also ignored the sodium sulfite clearing bath post bleach. Using 40g of SS each dev seemed like overkill. Additionally, I should mention a liter of TF-5 cleared 18 rolls of CN satisfactorily @6min fix.

Now I can focus on the other (various!) inaccuracies and undesirable imperfections in my processing. Thanks for the help, this has all been very informative.

koraks · Mar 15, 2025

originalwinslow said:
sodium sulfite clearing bath post bleach

That should have been before the bleach anyway, not after it. You could reuse the sodium sulfite for a while, although it'll oxidize over time.

Anyway...so good that you've been able to solve the issue! Let's hope it stays away, too.

originalwinslow · Mar 15, 2025

I still used 20g in the one-shot stop bath before the bleach. I thought someone said 20g/L in a clearing bath after bleach as well? Perhaps I misunderstood.

If I use a sulfuric acid stop (reusable) I can dump 20g of sodium sulfite in there and that will keep for a while?

lamerko · Mar 15, 2025

For a long time I used ferricyanide bleach for ECN-2 films. My process was basically as described by Kodak - stop bath with sulfuric acid, no sulfite, BUT with a long wash after the stop bath. Since temperature control is not so important afterwards, I just took a short break during the wash. The same after the bleach - this is mainly to protect my fixer. For a while I tested an additional bath with sulfite to shorten the time for intermediate washes - it worked perfectly with 20g/liter. Eventually, I found a supplier of C-41 bleach for minilabs - I now use only it and my process is much faster.

koraks · Mar 15, 2025

originalwinslow said:
If I use a sulfuric acid stop (reusable) I can dump 20g of sodium sulfite in there

You'll get a potentially dangerous amount of sulfur dioxide gas. If not dangerous, it'll at least be very uncomfortable and it won't achieve what you're looking for.

originalwinslow · Mar 15, 2025

koraks said:
You'll get a potentially dangerous amount of sulfur dioxide gas. If not dangerous, it'll at least be very uncomfortable and it won't achieve what you're looking for.

Good to know! I will not try that then.

lamerko said:
For a long time I used ferricyanide bleach for ECN-2 films. My process was basically as described by Kodak - stop bath with sulfuric acid, no sulfite, BUT with a long wash after the stop bath. Since temperature control is not so important afterwards, I just took a short break during the wash. The same after the bleach - this is mainly to protect my fixer. For a while I tested an additional bath with sulfite to shorten the time for intermediate washes - it worked perfectly with 20g/liter. Eventually, I found a supplier of C-41 bleach for minilabs - I now use only it and my process is much faster.

How long of a wash?

After transitioning to this new workflow I'm only managing one dev cycle an hour including spooling and hanging. If I mix 1500ml of chemicals that's 5 rolls in my big Paterson tank, but 5 rolls require even more wash time. Probably 1/3 of developing time is now spent washing, and that could be mostly eliminated by using standard c-41 bleach. I'm working on that, but as I mentioned sourcing those chemicals in powder form and in reasonable quantities is still on the to-do. I can order kilograms of PDTA from India but that would only make sense for me if I was going to mix bulk quantities of bleach to potentially distribute to other photographers in the community here. That's all a ways off.

At least ferri bleach has the upshot of 3~ minute soup time and long usable lifespan. I have considered collecting/filtering rainwater to reduce my water usage now that all this additional washing is required...it's about 4 gallons per cycle.

yonsama · Saturday at 8:37 PM

originalwinslow said:
안녕하세요 여러분.

최근 홈브루(Homebrew) 작업을 시작했는데, 제가 직접 만든 페리시안화 표백제를 코닥의 "대체 표백제"인 페리시안화칼륨 40g과 브롬화나트륨 25g을 혼합한 혼합물에 섞어 포뮬러리 TF-5 고정제로 고정하기 시작했습니다. 이 조합으로 ECN-2 현상액(ECN-2)을 현상해도 아무런 문제가 없었습니다. 하지만 첫 번째 C-41 현상액에서 일부 프레임에 네거티브의 저노출 부분에 미세한 얼룩이 생겼고, 스캔 결과 녹색으로 나타났습니다. 4일 후 두 번째 현상액을 현상했는데, 안타깝게도 네거티브에 훨씬 심한 빨간색/보라색 얼룩이 선명하게 나타났습니다. 포지티브 필름의 녹색이 더 뚜렷했지만, 네거티브의 노출 부족 부분에서도 대부분 눈에 띄었습니다. 다시 표백하고 고정했지만 네거티브 필름에는 눈에 띄는 변화가 없었습니다. 이 얼룩의 근본 원인을 찾기 위해 노력하고 있는데, 세척이 불완전했거나 정지액의 산성도가 충분하지 않았기 때문일 수 있습니다. 표백제와 고정제 혼합물 2L에 20롤 이상을 넣어 세척한 결과 이미지가 완전히 선명해진 것을 알려드립니다.

RPC와 "사진 기술" 문서는 C-41 페리시안화물 표백제에 페리시안화칼륨 80g에 브롬화칼륨 20g을 사용할 것을 권장합니다. "사진 기술" 문서는 이 더 강한 혼합물의 pH가 5.7이어야 한다고 명시하고 있는데, 이는 제가 사용한 40/25 ECN-2 페리 표백제의 pH 6.5보다 더 산성이어야 한다는 의미입니다. RPC는 표백 시간을 2.5분으로 명시했는데, 이는 pH가 낮아 더 강한 표백제가 생성되기 때문일 것입니다. 또한 그는 이 표백제를 두 번 사용하고 버린다고 하는데, 제가 사용한 "약한" 혼합물은 20롤 이상(물론 2L의 작동 용액을 사용했음에도 불구하고)을 완전히 세척할 수 있었던 것으로 보아 이는 낭비라고 생각합니다. FPP는 키트에 페리 표백제를 사용하며 20롤용으로 평가합니다.

이러한 요소들을 고려했을 때, 이 얼룩의 원인은 무엇일까요? 표백제가 미량의 현상액과 반응하여 시안화수소를 생성했을까요? 정착제가 미량의 표백제와 반응하여 프러시안 블루를 생성했을까요? 각 단계 사이에 3~4번씩 헹구고 있습니다. 식초 정지액(물 875ml에 5% 식초 125ml)이 너무 약했을까요? 정지액을 씻어낸 후 물에서 평소보다 파란색이 더 많이 보였습니다. 프러시안 블루를 연상시키는 것 같았지만, 네거티브 필름에서 어떻게 보일지, 그리고 표백제/고정액과 접촉했을 때 어떤 현상이 일어날지 설명하는 시각적 자료는 찾을 수 없었습니다. 또한 순수한 CD-4가 물과 섞였을 때 생성되는 짙은 파란색처럼 보였지만... 그것도 말이 되지 않습니다.

첫 번째 단계는 모든 새 화학 약품을 혼합하고 더 철저히 헹군 후 문제가 지속되는지 확인하는 것입니다. Psfred는 표백제의 pH도 얼룩을 유발할 수 있다고 언급하며 이 문제에 또 다른 의혹을 제기했습니다. 붕사로 완충하여 수명을 연장할 수 있지만, 표백제의 이상적인 pH 범위는 얼마일까요? 40/25 혼합액은 6.5 ± 0.5, 80/20 혼합액은 5.7 ± 0.5입니다. 제 2L 40/25 용액은 20번 이상 롤오버한 후 5.8로 떨어졌지만... 처음부터 얼룩이 생겼기 때문에 그게 원인이라고 생각하지 않습니다. pH 편차가 얼마나 되면 얼룩이 생길까요? 다시 한번 말씀드리지만, ECN-2에도 이와 동일한 방법을 사용했고 아무 문제 없었습니다.

긴 글 죄송합니다. 도움 주시면 감사하겠습니다. 저는 푸에르토리코에 살고 있는데, 비용 효율이 낮고 종종 품절되는 1L 파우더 키트에서 벗어날 방법을 찾고 있습니다. 액상 화학 제품은 여기로 배송되지 않습니다. EDTA/PDTA를 구하는 대로 원글님 말씀대로 블릭스를 섞어 사용할 계획입니다.

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Color cast problem with DIY color negative chemistry

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Flipping the movie – Color negative inversion process video – Koraks tinkers

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Color cast problem with DIY color negative chemistry

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