Developing B&W films to positive without second exposure

[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.