Developing B&W films to positive without second exposure

[wootsk]

Hi, I am asking if anyone here can guide me on developing B&W films to positive films without second exposure. I used to see some B&W films (Neopan 400 if I am not wrong) being developed as sepia looking positive before and was told that it can be done without having the need for a second exposure. But I am not sure of the chemical needed and the process.

Thanks a lot for those that reply.

 

[holmburgers]

Sodium Sulfide.

Here's (there was a url link here which no longer exists) explaining its use, from (there was a url link here which no longer exists).

I think this is what you're referring to, right?

 

[wootsk]

Thanks alot, I will read it up and try to understand.

 

[holmburgers]

My pleasure!

Their is some good information after the post I linked to, explaining his procedure in more detail. Someone else can probably give a better explanation, but the sodium sulfide "fogs" every silver-halide that remains (just like light) and at the same time develops it to a lovely brown color.

 

[Relayer]

sepia bw-slide step by step:
1) developing
2) stop
3) sepia fogging developer 3min:
Thiourea 5g
NaOH 10g
Water 1l
4) bleach 3-5min in:
Potassium dichromate 12g
Sulfuric acid 10ml
Water 1l
5) clearing bath 2min:
Sodium sulfite 30g
Water 1l
6) wash

 

[mrred]

Shouldn't step 3 be the last? You need 4 & 5 to be done before the fog.

 

[trexx]

Shouldn't step 3 be the last? You need 4 & 5 to be done before the fog.

No, the Thiourea bonds with the undeveloped silver, not the converted silver. Now there is a Black and Sepia piece of film. The bleach does not effect the sepia portion but removes the silver. A very clean process.

 

[Jeff Bannow]

Doesn't it need to be fixed somewhere in that process?

 

[wootsk]

Doesn't it need to be fixed somewhere in that process?

Ya, I also wonder why it doesn't need to fix or harden after an acid run. Won't emulsion be soft?

Thanks to those who reply. I also found some solution online. It seems that the formula is quite the same as the one above except the process step is different, but I doubt there will be any difference since the bleach only remove processed silver by normal B&W developer (Correct me if I am wrong). Also, it seems that you can sub Sulphuric Acid with Sodium Bisulphate. Correct me if I am wrong, but powdered chemical are easier to find in smaller quantity than liquid. I can get 5kg of it from a local pool equipment supplier than taking the trouble to filter used car battery.

 

[Relayer]

Doesn't it need to be fixed somewhere in that process?

fix isn't required in this process

No, the Thiourea bonds with the undeveloped silver, not the converted silver. Now there is a Black and Sepia piece of film. The bleach does not effect the sepia portion but removes the silver. A very clean process.

trexx, you right. really you can change sequence fogdev-bleach-clear-wash to bleach-clear-wash-fogdev with same result. but interesting that bleach as final step allow to process C41 color negative film as bw-slide and decrease density of orange mask. for process C41 film I'm recommended change bleach to more concentrate:
Potassium dichromate 50g
Sulfuric acid 30ml
Water 1l
process 5min

 

[Jeff Bannow]

fix isn't required in this process

Very interesting. Thanks.

 

[holmburgers]

FWIW, fixing is recommended by Haist and other authors too I'm sure. It shouldn't matter in theory since you've removed the negative silver image and developed the positive silver image, leaving no substantial amount of silver-halide.

But, there are always a small number of silver-halide grains that are orders of magnitude less sensitive (if at all) to light, and thus don't develop. Haist recommends fixing, and the hardening aspect is an added (if not needed) bonus.

 

[Relayer]

all silver halides that rest in emulsion after 1st developing sepia bath convert to Ag2S. nothing to fix

 

[anikin]

sepia bw-slide step by step:
1) developing
2) stop
3) sepia fogging developer 3min:
Thiourea 5g
NaOH 10g
Water 1l
4) bleach 3-5min in:
Potassium dichromate 12g
Sulfuric acid 10ml
Water 1l
5) clearing bath 2min:
Sodium sulfite 30g
Water 1l
6) wash

What concentration of sulfuric acid should be used here?

 

[holmburgers]

1% sulfuric acid final solution is standard I believe; so usually when it's listed without a % you can assume they mean concentrated (96+%) unless otherwise stated.

Relayer, you're probably right, and maybe more so given the sepia treatment, but there was more to Haist's push for fixing than I can't remember at the moment.

 

[Relayer]

in all formulas used concentrated sulfuric acid

 

[anikin]

Got it. Thanks! This looks like the easiest way to make positive b/w. Thank you guys for posting this. Are there any downsides for using this method to make enlarged negatives for alt processes? Also, does this method require exposure adjustment?

 

[holmburgers]

Personally I don't think that the 2nd exposure or 2nd development is too difficult, but I don't have any sodium sulfide on hand.

With Delta 100 & TXP320 I found that +1/2 or +1/3 EI worked best.

 

[mrred]

Personaly I use traditional selenium tone (1:3) after fix and wash. It works great. I looked at a fogging dev, but it really isn't that big of a deal for me. It also allows me to bail earlier when things don't work out.