Another thing to point out... you could improve the Dmax by adding potassium bromide as well. I have not spent much time on that in this process yet, but if you get all the other variables right that's another you can tune.
BnW reversal attempts
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Thiosulphate is a halide solvent and it is used to remove some but not all unexposed halides. In your case, thiosulphate has removed all the unexposed halides leaving nothing for the second developer to produce a positive image. Ilford's recommendation of 8g/l is for a specific Ilford film and doesn't generalize to all films. One needs to test and figure out the optimum concentration of thiosulphate for each film. In the specific case of Scala 160, you'll probably not need so much thiosulphate. Start with small amount, say 1g/l, extend the development time if needed, see what you get and take it forward from there. For the purpose of testing, use only a short strip of film instead of an entire roll and expose some normal contrast scenes on it.
Thanks for the advice Raghu. I will certainly cut back the thio! I am curious though why you suspect that Scala 160 won't need much.
I will keep the addition of potassium bromide in my back pocket for once I've optimised my current recipe. Could you give me a rough idea of how much to use and whether other aspects of FD need to change?
Thanks!
Thanks!
I have checked MSDS of Scala reversal kit which is Adox's recommended processing kit for Scala films. There's no mention of either thiocyanate or thiosulphate. If the film needed 8g/liter of thiosulphate then the kit would have had 16g which would have found a mention in MSDS.
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Got it! I am only just starting to learn about film chemistry not to mention reversal! I was assuming that the thiosulphate was only needed for reversal development. Now I realise it is found in many commercial developers. Seems I can learn a lot looking at MSDS sheets! Thanks for your help..
Sodium thiosulfate is fixer, if that makes it clearer what is happening. It's not "rapid" fixer, that's ammonium thiosulfate, but it has the same effect as your normal fixer, just at a slower rate. It's not normally in developers except in reversal.
Thanks for the clarification! I now understand where Raghu was coming from referring to the MSDS fro Scala's own reversal process.
I can see that jumping into reversal processing without understanding regular B&W processing is a bit like walking in half way through a movie. I am that annoying guy asking 'who's that character?' 'why did she do that?' etc. ;-).
To save you further pain can anyone recommend a resource (online or in print) that describes what is in film processing chemicals and what each component does? I have googled the topic but just come up with very basic articles. Thanks!
To save you further pain can anyone recommend a resource (online or in print) that describes what is in film processing chemicals and what each component does? I have googled the topic but just come up with very basic articles. Thanks!
I'll DM you
Generally I recommend the Film Developing Cookbook by Anchell and Troop as a good starting point here. Steven Anchell's The Darkroom Cookbook is another good place to start.
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Thanks for the tip! I am pleasantly surprised to see that Film Developing Cookbook got a 2nd edition in 2019 so I can buy new. It does look very good from the Amazon preview
I followed your lead...I tried PQU 1+5 with 3g/l sodium thiosulphate on a roll exposed at ASA 160. I cut the strip in two and tried 9 mins and then 10 mins FD. The results for 9 mins were too dark and lacking on contrast. It was a gloomy afternoon though. The second half of the film was shot on quite a sunny afternoon and 10 minutes FD. These were much better and a very subjective 7/10. Thanks for the tip! The blacks aren't bad but it's the highlights that are lacking most I think. And by the way, the processed film has a yellowy tint. I won't mess with that just yet but I suppose a longer or more aggressive clear bath is required.
I am now musing on what to try next More or less sodium thiosulphate? A bit longer FD? Neither of the above? I am reluctant to introduce another element in the mix like potassium bromide without being sureI have got the most out of what I am already using. Any thoughts?
More thiosulfate and/or longer first development will lighten the slide, and the former will clear the highlights relatively more than the shadows.
What kind of bleach are you using? The PQ developer should have accessed all the silver halides so if your highlights aren't clear then it could be a bleaching issue. Also what/how much are you using for the clear bath?
One thing to keep your eyes on is the film border (i.e. where they have the film brand name and frame number). If that portion is not completely clear then it's either a developer or bleach issue (though I doubt it's the developer in this case).
@Eddypolak I agree with what @YoIaMoNwater said. Here's a photo of that roll of Scala 160/Silvermax 100 that I discussed above. This is after bleach, just before re-exposure. Was yours this clear? Note the leader at the very top and wrapped around the spool: totally clear. You can see the white highlights here as well, for comparison.
@Eddypolak: I surely don't want to discourage you from experimenting, but for Scala 160 film there's a simple solution to the problems you're facing: scala reversal kit. It is expected to be back in stock in the second half of this month and is probably worth the wait. If one has not seen well made slides, then clear highlights, contrast, deep blacks, mid tone contrast etc are all mumbo jumbo. Scala reversal kit reportedly gives you a painless way to get good slides. You can always experiment with your own chemistry later and you'll have a good benchmark to compare your results against.
Thank you all for being very helpful and informative! The back story here is I bought a bunch of Scala 160 and then found I couldn't get the kit! So coronawhile I thought I might as well pick up where I left off with the Ilford process and Pan FPlus during the first lockdown 
I will surely buy the kit once I can and indeed get a true benchmark set of results but I like experimenting and using my brain (and those of others!) so I will carry on with this a little bit longer. It is very true that I have struggled with the language of describing the results with this benchmark. Who will/would be stocking the Scala kit in the UK?
I've only looked at my film once it's been through the clear. It looks a creamy white but I haven't examined it in any detail. The final film has a perfectly transparent leader with a slight yellow tint I naturally see in highlights. If 'film border' is the same as where the sprocket holes are that is perfectly black which is I would have expected since it's not been exposed so I am confused that it should be clear.
My bleach and clear are as per the Ilford method. So that is Bleach A potassium permanganate 4gm/l Bleach B 10% sulphuric acid diluted 1+4.which I mix at the time of processing. The only doubt is percentage concentrations are no long used but I have calculated that 1M acid is equivalent to 10%. The clear is 25gm/ l sodium metabisulphate.
So given the faint tint do you think that is a bleach or clear issue?
I will surely buy the kit once I can and indeed get a true benchmark set of results but I like experimenting and using my brain (and those of others!) so I will carry on with this a little bit longer. It is very true that I have struggled with the language of describing the results with this benchmark. Who will/would be stocking the Scala kit in the UK?I've only looked at my film once it's been through the clear. It looks a creamy white but I haven't examined it in any detail. The final film has a perfectly transparent leader with a slight yellow tint I naturally see in highlights. If 'film border' is the same as where the sprocket holes are that is perfectly black which is I would have expected since it's not been exposed so I am confused that it should be clear.
My bleach and clear are as per the Ilford method. So that is Bleach A potassium permanganate 4gm/l Bleach B 10% sulphuric acid diluted 1+4.which I mix at the time of processing. The only doubt is percentage concentrations are no long used but I have calculated that 1M acid is equivalent to 10%. The clear is 25gm/ l sodium metabisulphate.
So given the faint tint do you think that is a bleach or clear issue?
I have answered my own question re UK dealers....
It could be residual silver from the first development due to insufficient bleaching. Or it could be silver formed by second development due to rehalogenation in the bleach. There's also a third possibility where some of the silver removed by the bleach doesn't diffuse out fully and gets trapped in the gelatin mesh. This happens when the bleach is not properly formulated or has been reused several times.
Extend the time in bleach by a minute and see if the tint goes away.
Rehalogenation can happen when bleaching if there are halide impurities in the bleach. Some silver in the negative image gets converted to silver halide which is redeveloped by the second developer. Use distilled/RO water for mixing the bleach.
To avoid the third possibility, mix the permanganate bleach afresh every time and don't reuse it.
BTW if you still have the leader with you, try bleaching it again with lights on, clear and redevelop to see if the stain goes away.
Thanks again for more great info! Nothing s ever simple is it? I do mix the bleach fresh every time so that's one less possibility. I do have the leader so I will try what you suggest. If it clears then that means longer bleaching needed in the process right?
Plausibly.
When I say film border I meant the letterings/numberings along side edges of the film. This part should be relativity clear, in this case Scala 160 should be the same clearness as the film leader portion. Can you post some pictures of the film leader region and some shots where you think the highlights aren't as clear?
Will shots of some pics on a light box work? To be clear (no pun intended!) there are two issues. One is a yellowish tint which appears throughout the film where like the leader it is close to transparent. The other issue is that highlights are light grey when projected and not white on screen. Language is tricky isn't it? I guess the posting pics is a lot better!
Yea it's prob best to show these on a lightbox.
I'm afraid that I can't produce a useful image using my phone and slide on a lightbox. I have looked closely at the frame numbers in the border and they are not perfectly clear. Time for me to reflect a little on what avenue to follow next. Thanks again for you help!
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