DBI; Desensitizer

Steve Hamley · Dec 30, 2005

Folks,

I was chatting with a long time commercial photog recently, and he told me that he used to do B&W development-by-inspection under a regular red safelight after using a desensitizing solution which was a potassium permanganate solution, 1 percent he believes. He also said Kodak used to sell such a product, which he stated looked like potassium permanganate. Anybody done anything like this?

This fellow is a really interesting person to talk with. he's been a commercial photographer for 66 years and started off when people were still using flash powder. He currently uses 4x5, MF, and digital. He'll be 84 years old in February and still gets excited about photography, working about half time.

Steve

htmlguru4242 · Dec 30, 2005

I've never done this, though I've heard if it being done. There is a desensitizing dye out there that I believe is still sold by one company. It's calles phensofranine or something along those lines. There was a post here on it a while back, I'll check to see If I can find a link ...

htmlguru4242 · Dec 30, 2005

Ah, here we go ... here's the thread I mentioned in my last post...

(there was a url link here which no longer exists)

Steve Hamley · Dec 30, 2005

Thanks, D-Tec sounds like potassium permanganate (staining, possible irritation).

Steve

htmlguru4242 · Dec 30, 2005

Actually, from looking around online, it seems to be a dye called Pinakryptol. The D-Tec seciton on the manufacturer's web site says that it is a synthetic dye, which seems to rule out potassium permanganate. I'm not 100% sure, though.

I believe you can buy it as D-Tech or from Photo. Formulary.

Charles Webb · Dec 30, 2005

Did he mention Orthochromatic or Panchromatic film. I would be interested to know if this was or could be done with Pan film. I know when Pan replaced Ortho, we also switched our red safe lights for green ones. Never a problem with Ansco, Gevaert, Royal Pan or Royal X Pan using a dark green safe light several feet from the tanks after the developing was past half it's regular developing time. Sure would like to know more about what he was doing.

Charlie.......................

eumenius · Dec 30, 2005

My own experience with desensitizing dyes was using Safranin T dye, the one used in light microscopy staining of specimens. I presoaked the Fomapan 100 film in its weak solution (well, about the color of cranberry vodka, you know ), then switched the sodium lamp on, and developed it with visual control with no problems. No fogging, none at all. The main thing was this all-penetrating red colour, my hands and trays were red - and it was a trouble to wash it completely from the emulsion. It took a soaking in 2% acetic acid and long wash to complete. I didn't try to soak it in ammonia solution, maybe that would have made it faster. But frankly, I can't see any application of desensitization of Pan films for me, so I quit doing it after satisfying my interest.

Ole · Dec 30, 2005

I have a gram of Pinakryptol which I bought for desensitising.

I haven't used it - DBI works fine without it.

Helen B · Dec 30, 2005

The desensitisers that I'm aware of are:

phenosafranin(e) (red-violet) - used from 1 : 2 000 to 1 : 10 000, forebath or developer additive, doesn't work with hydroquinone, reduces the activity of pyro and amidol, OK for ortho, may not work with pan

phenosafranin + chrysoidin (in equal parts to give basic scarlet N, red) - used at 1 : 5 000, forebath only

pinacryptol green - used at 1 : 5 000, as a forebath only, works in the red sensitivity region so it is suitable for pan film, totally stops development in a dev containing pot. thiocyanate (eg DK-20)

pinacryptol yellow - used at 1 : 1 000 or 2 000, as a forebath only, more effective than green especially for pan emulsions

pinacryptol white - used in the developer

These are dyes that adsorb to silver halide and decrease its sensitivity to light. The colour of the dye is not important: its ability to adsorb strongly onto the silver halide is. They appear to affect the sensitisation by other dyes more than they affect the silver halide itself, so the inherent sensitivity of the silver halide to blue light remains.

It strikes me that potassium permanganate on its own could attack the latent image as well as the sensitivity nuclei. Potassium iodide works, if it is in the presence of pot. thiocyanate and sodium sulphite to prevent destruction of the latent image, but the dyes work better.

Best,
Helen

Ole · Dec 30, 2005

Thanks for that summary, Helen - I'll keep that one!

Potassium permanganate is a strong oxidising agent, and not something I'd think would be useful in a reducing solution - which is what a developer is?

vet173 · Dec 30, 2005

If you develop in pyrocat-hd, the developer acts as a desensitiser. Nothing need be added for DBI.

Steve Hamley · Dec 31, 2005

Try inspecting DBI with a green light on HP4+ in Pyrocat for more than a second or so. You will be underwhelmed.

Steve

Photo Engineer · Dec 31, 2005

Potassium Permanganate is indeed a strong oxidant.

Use in a developer will immediately destroy the developer making it useless.

Use as a prebath will oxidize the latent image back to silver oxides destroying the image, and if any is carried into the developer, the developer will be destroyed as well, rendering the developer useless for other films to follow.

PE

fhovie · Dec 31, 2005

sodium permanganate as a presoak will add one stop. - been there - done that - it works

Add 166ml of 3% peroxide to water to make 500ml solution - add 5g Sodium Metaborate - Presoak the film for one minute in this solution before development

Helen B · Jan 1, 2006

fhovie said:
sodium permanganate as a presoak will add one stop. - been there - done that - it works

Add 166ml of 3% peroxide to water to make 500ml solution - add 5g Sodium Metaborate - Presoak the film for one minute in this solution before development

Permanganate? Where's the manganese? I think that you mean perborate. You've described perborate latensification.

Best,
Helen

Photo Engineer · Jan 1, 2006

Helen B said:
Permanganate? Where's the manganese? I think that you mean perborate. You've described perborate latensification.

Best,
Helen

fhovie, what she said!

Don't make that error for real. Permanganate is bright blue-purple, and is a powerful bleach. It is used to bleach silver images and was once used in color processes. Perborate is colorless.

Permanganate, upon heating, can cause fires and even explosions under the right (wrong - depending on POV) conditions.

PE

DBI; Desensitizer

Steve Hamley

htmlguru4242

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Steve Hamley

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Charles Webb

eumenius

Ole

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Helen B

Ole

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vet173

Steve Hamley

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fhovie

Helen B

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DBI; Desensitizer

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