FP4 pre-soaking (dye?) - 120

Hi there,

Curious question.

Normally I pre-soak 35mm FP4 in water at a similar temperature to the dev/fix for about five minutes - just done this usual procedure with 120 FP4 and the watr was dark coloured when I poured it out. Is it a dye?

I have never had this with 35mm, what is it? Why on 120 and not 35mm? Should 120 not be pre-soaked but 35mm ok to pre-soak?

Any thoughts or preferably answers welcomed!

Cheers,
Sim2.

You have just stepped into a subject matter that is argued on both sides with religious fervor. We have on one side the pre-soakers; on the other side we have the non-soakers. Stand back and watch the fur fly.

Steve

Don't worry, its just the anti-halation layer being washed off.

Thanks, guessed it was like a dye thing - anti-halation eh?

What is the purpose of tha layer? Any reason for keeping it by not pre-soaking? Any reason why it's not evident on 35mm FP4 film?

The anti-halation layer keeps light from passing all the way through the negative and then reflecting off the pressure plate and back onto the film (exposing it a second time -- especially in the highlights.) Instead, the layer sort of absorbs the light. Kodak's infra red film had no anti-halation layer -- thus the highlights tended to glow from the extra exposure.

Different bases perhaps are used for 35mm and 120? so the anti-halation layer is handled differently?

Vaughn

A technical learning curve here - cheers for the input, that makes sense as I think 35mm is coated onto a layer which isn't on 120 ewhich needs the paper backing to replicate this. Perhaps?

Still learning. :munch:

The only films which may not have the anti-halation layer is the LF films. Some have the layer and some do not.

Steve

Sirius Glass said:

You have just stepped into a subject matter that is argued on both sides with religious fervor. We have on one side the pre-soakers; on the other side we have the non-soakers. Stand back and watch the fur fly.

Steve

Click to expand...

True, but consistency is the important thing here. If you pre-soak, always pre-soak. Include it into your film development test, because it affects development. Don't test with it and develop without it or visa versa, and you'll be fine.

I agree with the consistency. Just a bit scary to see "dark" water coming out when it is not expected - especially as it has not been seen before on other formats.

Have heard that newer films such as delta should not be pre-soaked as the dye is "used" by the dev. Fishmongers tales or gospel truth?

Do not be alarmed. It has to come out some time. It if doesn't come out in the initial rinse water, it comes out in the developer. If you do not pre soak, you see this same thing when you pour out your developer.

If you don't pre-soak, you might not see it come out with the developer, but rest assured that the AH dye has been removed. I don't know why exactly that these AH dyes are bleached in the developer, but they are in most cases. The most egregious example that I've seen of the dye not being bleached occurs with 35 mm APX 100 developed in Rodinal with no presoak. I suspect that the sodium sulfite contained in many developers is responsible for the bleaching action, and since a working dilution of Rodinal has very little sulfite, no bleaching occurs. At least that's my line of reasoning on the subject.

In any case it doesn't really matter. I'm in the camp that doesn't pre-soak unless I'm processing sheet film in trays. But hey, whatever works for you is fine. I temper my tank in the same water bath that I use to temper my chemistry, so the tank and the developer are the same temperature and stable when I start the process. Plastic tanks want to float, and that's ok. I just weight it down with a 1/2 brick, then use that brick as a base for the tank in the tempering bath to raise it up high enough out of the water so it won't float when it's partially filled with developer. Easy - no muss, no fuss, and temperature is tightly controlled.

I can't recall a MF film that doesn't do it. Some are green, some are blue, some are purple. I'm in the camp of pre-soaking my MF film and don't do it with 35mm.