Black spots when reversal processing

First off, I just want to say thank you so much to all of you great people here on APUG, in particular Alessandro Serrao, Jordan W, amuderick (also Julio1fer and ImageMaker from photo.net). I successfully reversal processed some b&w films for the first time. Very rewarding and fun experience!

My process was:
Dektol 2+1 develop 10mins (to completion)
Wash
Potassium permanganate bleach (acidified with sodium bisulfate) 5mins (to completion)
Wash
Potassium metabisulfite clearing bath 2mins (to completion)
Wash
Clear highlights by inspection sodium thiosulfate 25g/L
Wash
Exposure to light
Dektol 2+1 Redevelop 5mins (to completion)
Wash
Photoflo rinse

I processed three rolls of PanF+ -- one exposed at each 25, 50 and 100 ISO. Time spent in the hypo bath was slightly different: 2m15s, 2m:30s, 3m45s respectively.

I like this process (suggested by ImageMaker) as it reduces everything to one variable -- the length of time in the highlight-clearing hypo bath.

I did however identify one shortcoming somewhere in my process. Many of the frames have pinpoint black dots on them. (I have verified they appear on the film and not only the scans I uploaded) There are very small, and are not of much concern to me, however, I thought I'd check to see if anyone has some suggestions on how to eliminate them.

APUG is really something special, I can't tell you how much I've learned from the archives. Thanks so much for this space and all you great folks.

I made test with Aviphot Pan 400 S PE 1 processed as slide b&w.
https://www.flickr.com/photos/21121448@N06/16195263396/
https://www.flickr.com/photos/21121448@N06/11964580136/
I also had problems with black spots that appear on the emulsion.
They come from black on deposit support (graphite).
Agfa recommend washing before developing.
I used a prebath with sodium carbonate and washing before developing.
There are still a few black spots.

George

georgegrosu said:

They come from black on deposit support (graphite).
Agfa recommend washing before developing.
I used a prebath with sodium carbonate and washing before developing.
There are still a few black spots.

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I did some medium format PanF yesterday and also had this problem with spots. I will definitely add a pre-wash to my process.

Alessandro Serrao said:

Probably a manganese dioxide leftover from the bleach. Check out if there's precipitate in the mixed bleach. Or check the strenght of the clearing bath.

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There was some amount of brown preciptiate (MnO2) in the bleach. What can I do to avoid this? I used distilled water and only mixed the acid and the pot perm ~30 seconds before using.

I know most folks use a sodium metabisulfite as a clearing bath. Do you know if there is any difference between sodium metabisulfite and potassium metabisulfite? Ilford says either of them work, and suggests the same dilution (25g/L), which doesn't make total sense as the potassium version has 115% the molecular mass of the sodium variety. I may try a stronger clearing bath, or more time. I can't find their solubility product constants anywhere on the web.

Thanks for your help.

Alessandro Serrao said:

The difference between sodium and potassium salts is mainly solubility in water.
To circumvent the bleach problem you should use permanganate that is reagent grade, the purest. That goes also for the bisulfate (I'm assuming you're using the ph down thing).
You can however filter the permanganate concentrate (the salt, not the acid) with a coffee filter for the time being. But really you should use reagent grade permanganate. And use all bath as one shot, never ever reuse anything.

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Do you mean filter the permanganate solution (ie: after mixing it in water)?

Alessandro Serrao said:

And use all bath as one shot, never ever reuse anything.

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Yeah, I didn't reuse the permanganate as it oxidizes easily, but I did reuse the clearing bath. I won't reuse it anymore.

Great, thanks.