Simple question, hard answer?

[nsouto]

Polaroid: how come they can develop AND fix with a single exposure to a single chemical bath and with traditional film we can't?
What's the secret?

TIA for any insights.

 

[keithwms]

There are monobath developers for 'normal' film...

 

[Alex Bishop-Thorpe]

In a word, monobath - a very well designed and effective monobath. From what I understand, the problem with monobaths and conventional film is that the chemistry has to be carefully fine tuned for each emulsion. I was reccomended the Monobath Manual, by Grant Haist, if you're interested in the topic.

 

[nickandre]

I don't believe the instant film "fixes" the image. I think it develops the negative image and the remaining dyes/silver move to the positive sheet. Peeling or a timing layer stops the process. Fuji has a PDF with their instant packfilms.

 

[Alex Bishop-Thorpe]

Peeling doesn't stop the process, you can try it for yourself. The development time labelled on the film is the minimum time. Take two photos of the same scene, peel one at the suggested time, and the other at 15 minutes, and there wont be a noticeable difference between them.

 

[Anscojohn]

Polaroid: how come they can develop AND fix with a single exposure to a single chemical bath and with traditional film we can't?
What's the secret?

TIA for any insights.

********
We can. Unibath developer/fixers have been around for a long time.

 

[Vaughn]

I don't believe the instant film "fixes" the image. I think it develops the negative image and the remaining dyes/silver move to the positive sheet. Peeling or a timing layer stops the process. Fuji has a PDF with their instant packfilms.

Would not explain Type 55. Both positive and neg are fixed.

 

[cmacd123]

The peel appart Poloroids are a process called "difusion Transfer Reversal" all the silver ends up in the negative or the print so their is little for a fixer to do. In the most common case the print only gets the image silver. The Type 55 did need an extra step to stabilize the neg. Most of the films also had a coater to stabilize the print.

 

[nsouto]

I do recall at some stage Polaroid had an "instant" slide film, with its own processor box. Mid 80s? A very simplified process, IIRC.

I'm just curious towards all this. After all: doing my own development of b&w, I'm only too familiar with the issues of timing, developer concentration, agitation, fixing, washing, and what not.

Yet the folks at Polaroid managed to get around all those problems in one single step. Amazing!

And the quality was quite acceptable, IIRC. At least in B&W, if not colour as well. May be not in slides, I don't think the instant version was that popular?

Still: an amazing state of affairs and one that baffles me to this day. How come no one seems to experiment with these Unibath processes and refine them? Or am I looking in the wrong places?


Like I said, not a major subject: just decided to "shoot the breeze" on this one. Thanks for all the interesting information.

 

[Steve Smith]

Yet the folks at Polaroid managed to get around all those problems in one single step. Amazing!

I have the Edwin Land biography 'Insisting on the Impossible'. In that book, there is an explanation of how the black and white diffusion process works which I can just about understand. Then it goes on about colour and I am lost!


Steve.

 

[nsouto]

Thanks for the pointer to the book, I'll definitely look it up.

 

[bdial]

That book is a great read, and has good, simplified explainations of how the Polaroid processes work.

 

[bsdunek]

Just shows that there are some really smart people in this world. I barely scraped through chemistry in college, so they have my respect!

 

[keithwms]

That is a nice book, a bit long in parts, but it contains some good insight into Land's experimentalism and just how hard he worked (and with a tremendous amount of faith that it was all worth something). The most enjoyable tidbit for me was to see how he was motivated by one child's simple question of where does the image go and why can't we see it right away.

Form the book, it's not clear that we know yet just how much Land worked on satellite recon, and how close the relationship was between Polaroid and the military or whether it was just an ongoing individual consulting gig with little money attached. I would guess that he would have been absolutely worshipped by the recon community.... the technology he had would have made almost real-time high res imaging possible, a very big deal during the Cold War. Maybe others were convinced that they didn't need his partnership- Kodak certainly had some heavy hitters too.

That is an interesting piece of history that is, as far as I know, still untold. Also lacking in the book was the kind of detail needed to understand the patent wars with Kodak, but that would of course have made the book far more technical.

Overall, an excellent read and a nice Christmas gift!

 

[BobCrowley]

Haist's book has a number of monobaths that are similar to the reagent used in Old Pol's Type 55. Meanwhile, starting with Donald Quall's excellent HC-110 based recipe, we pH tuned a reagent that we use successfully on Efke 25, TMX, and Pan-F. The Efke monobath/reagent works in 2 minutes and the others in about 6 minutes.

Diffusion Transfer Reversal or DTR is indeed a powerful agent in the development of instant pack and sheet films, and acts like a powerful intensifier, so it needs a negative with little silver. Whatever Old Pol picked for 55, some insist it was Panatomic-X, it was a thin emulsion not too different from the Efke 25. If you look at an MSDS from T55 you will recognize it as similar to one of the monobaths in Haist, but with the addition of methyl cellulose to thicken it, and a little extra sodium sulfite to at least stabilize the negative.

There is a lot on the subject at http://new55project.blogspot.com especially posts 1-40 where a lot of the research into the reagents was discussed. Later on the blog are a number of examples of negatives processed in monobaths or reagents we've tried, the latest being reagent III, which works with Efke 25 fairly nicely.

 

[Gerald C Koch]

The newer Polaroid color prints were completely enclosed in plastic and depended on the migration of dyes formed during development to the front of the print. Fixing was not necessary in this case.

I too would recommend Grant Haist, The Monobath Manual. Besides discussing monbaths and giving a practical monobath formula there is a lot of good photochemistry in this book.