B&W reversal procedure

[SalveSlog]

The usual way to do B&W reversal is to first develop the negative image. Then bleach that away.

Should not some clever chemist be able to devise a more direct method that would just remove the latent image at once instead of developing it?

I know this may be a naive question. Just can't help asking.

 

[pdeeh]

How would the chemistry know which latent image to remove ?

 

[SalveSlog]

Well, I said I'm naive.. and not a chemist.
But how does the developer know which latent image to develop?

 

[removed account4]

hi salveslog

there are, and have been direct positive papers and processes
ilford made a direct postiive paper ( you expose it, and develop it as a positive, single step as they say )
they stopped making it for a while and rumor has it ( or maybe i listened to the fleetwood mac too much )
that it might start up again ? there are direct postiive papers currently being made in europe !
efke makes a paper, and imago ( maco ) makes some as well ( maybe they are the same ? i have no idea )
in years gone by there were proprietary developers that would develop, bleach and reverse photo papers that street photographers used
to make instant street portraits and post cards with ... that process was also called the silver gelatin ferrotype process and besides paper
they made images on metal (silver gelatin ferrotypes ) ... which were indisnguishable from wet plate tintypes ...


no need to really be a chemist, you just need direct positive paper

have fun !
john

 

[gzhuang]

How about shooting Agfa Copex and developing in Ultrafin?

 

[Gerald C Koch]

Well, I said I'm naive.. and not a chemist.
But how does the developer know which latent image to develop?

There is only one latent image and that is the negative. I think that this is where your reasoning went astray. The positive image consists of all the unexposed silver halide that is left in the emulsion. So you must first develop the negative image. Once it has been converted to a non-reactive form the positive image can be developed. A simple way to do this is with a fogging developer. This converts all the remaining silver halide to silver. There is no significant difference between film intended for negatives or that same film intended for making positives. The only difference would be in the EI used.

It might be helpful to read Ilford's directions.

http://www.ilfordphoto.com/applications/page.asp?n=90

 

[SalveSlog]

Gerald,
the latent image is affected by the developer. The developer is a chemical substance. Why can't the latent image (the light-affected silver halide) be removed directly by a chemical substance instead of developed to silver grains first? Can someone explain why this is a chemical impossibility?

 

[pdeeh]

Because the latent image substance is indistinguishable chemically from the rest of the emulsion on the film - this is a gross oversimplification as the physics and chemistry involved is remarkably complicated and I don't understand a hundredth part of it, but Gerald does and his explanations are to be trusted

 

[SalveSlog]

I realize I will probably have to give in in the end..
But how can the developer find the latent image if it is "indistinguishable chemically"?

 

[Gerald C Koch]

The only way to get rid of the unwanted negative image is to develop it and then bleach it. The bleach converts it to a non-reactive form. Then the remaining silver halide (the positive image) can be developed. Finally the silver compound that is the negative image is removed with fixer. What is left is only a positive image.

As pdeeh states there is no gross chemical difference between the two images. Physically there IS a difference in some of the crystalline structure of the exposed portion of the emulsion. Exposure to light causes crystal defects that are slightly more reactive to reduction. That is how the developer "finds" them.

 

[Photo Engineer]

Direct reversal, as noted above, is the only method to get a positive image from Silver Halide. It is difficult and messy involving a complex emulsion making step that requires making a special type of core shell emulsion with two sensitizations on it, one internal and one external.

This procedure affects the allowable limits to grain size, speed and composition. With a reversal process OTOH, there is virtually no limit.

And the process can distinguish between exposed Silver Halide and unexposed, but it is difficult as Gerry points out.

PE

 

[Gerald C Koch]

The following article might be helpful. http://en.wikipedia.org/wiki/Latent_image

 

[michr]

Starting with exposed film, develop/bleach in one step and chemical fog in a second step? Will this create a transparency?

 

[Photo Engineer]

Starting with exposed film, develop/bleach in one step and chemical fog in a second step? Will this create a transparency?

Yes, now describe chemically how to do it. I cant and I'm a chemist. You need an oxidant and a reductant acting at the same time.

PE

 

[michr]

If you don't know how it can be done, I certainly cant'. Scratch that idea.

 

[SalveSlog]

Exposing my naivety paid off. So, thank you all.

I've read that it may not give the best results, but I guess I should start learning B&W reversal from the Ilford recipe(?)
It's clearly explained and ingredients should not be too difficult to find. Comments welcome..

 

[pdeeh]

I wanted to try reversal ages ago, and followed the Ilford pdf almost to the letter (I didn't have any Universal so I used print developer) and it worked almost perfectly first time.

So I'd say it's a very good place to start

Lots of people have their own variations of course, and there have been harsh words exchanged over the issues of hypo in the first developer and whether permanganate bleach is truly suitable, among other things ...

 

[Gerald C Koch]

The Ilford reversal system works well IF you follow their directions faithfully and make no changes to the baths. People who make changes usually wind up here on APUG asking what went wrong.

The Ilford permanganate bleach tends to soften the emulsion so pay attention to time and temperature in this bath.

Making B&W slides requires attention to correct exposure. Sloppy metering is compounded by the reversal process. When in doubt bracket your exposures.

 

[Oxleyroad]

The Ilford reversal system works well IF you follow their directions faithfully and make no changes to the baths. People who make changes usually wind up here on APUG asking what went wrong.

and use Ilford film!

 

[SalveSlog]

One more question while I struggle to obtain those chemicals..:
I want to use Delta 100. But I prefer medium format. Is Delta in 120 format different from 135 for reversal?

 

[SalveSlog]

So I finally got the chemicals and reversal developed my first film. I followed the Ilford recipe as close as I could, using Delta 100, 35mm.

Well, I never hoped for results like this on my very first attemt!
Sorry I don't have a scanner.
I see none of the problems we may read about on the dr5 website. So why do a beginner like little me get better results with the Ilford recipe than David Wood got with the same recipe? (He made me not try this for a long time. Grrr!)

Good God, I have to load my Zeiss Ercona 6x9!

 

[pdeeh]

Well done!
Now all you have to do is buy a 6x9 projector

 

[SalveSlog]

I better cool down before I take any decisions ...

 

[Gerald C Koch]

All B&W films are not suitable for reversal. You really need a colorless film base for slides. At one time Foma made a reversal film that was ideal for slides but they discontinued the 35mm size.

 

[SalveSlog]

You mean the 120 size? I think the 35mm is available.