OCT scanning for negatives

[koraks]

Single Colour Process, Stevens, A, Vol 149, No. 7389, 31. 7. 02

Is this retrievable anywhere apart from behind BJP's paywall?

 

[Helge]

The electronic interference patterns BBC used to retrieve low resolution colour information from telecined B&W film (because they went cheap with tape), inspired me to think about interference.
Lippman plates uses interference.
There has to be colour related interference patterns in first gen B&W material. However slight.
Question is how slight is too slight.

Also it could be theoretically possible to determine the placement of the sensitizing dyes in film. Even after development.
The key word here is of course theoretical.

 

[koraks]

There has to be colour related interference patterns in first gen B&W material.

Why? Lippman plates are made by having the silver halide emulsion in direct contact with a highly reflective surface. The reflections between this backing surface and the silver halide grains make for the interference pattern that records color. Regular film doesn't have this structure. Hence, there doesn't "have" to be remnants of such interference in regular film.

 

[Helge]

Why? Lippman plates are made by having the silver halide emulsion in direct contact with a highly reflective surface. The reflections between this backing surface and the silver halide grains make for the interference pattern that records color. Regular film doesn't have this structure. Hence, there doesn't "have" to be remnants of such interference in regular film.

The emulsion is in contact with the substrate. Plate or film. And also the grains are often in contact with each other.
Any interface change will result in reflection. It’s a matter of determining if it’s enough to say anything useful about colour.
Modern Lippman plates often uses airgaps as reflector. Think “silver” fingers on glass of water reflection type.

 

[Findlay]

Is this retrievable anywhere apart from behind BJP's paywall?

It doesn't seem so now, unfortunately. Some reference libraries stock it. I can maybe track down my copy, scan it and get and post a link when I get a moment.

 

[Findlay]

The electronic interference patterns BBC used to retrieve low resolution colour information from telecined B&W film (because they went cheap with tape), inspired me to think about interference.
Lippman plates uses interference.
There has to be colour related interference patterns in first gen B&W material. However slight.
Question is how slight is too slight.

Also it could be theoretically possible to determine the placement of the sensitizing dyes in film. Even after development.
The key word here is of course theoretical.

The interference approach sounds very interesting. Modern materials have a non reflective coat but older plates didn't. It may work together with my idea. Anyone know of a anyone with an OCT scanner to try it?

 

[koraks]

The emulsion is in contact with the substrate

Yeah. But the nature of the substrate matters, as does the emulsion topology. Neither are geared towards this kind of interference pattern in regular film.

Modern materials have a non reflective coat but older plates didn't.

In the process of making a Lippman plate, AFAIK the reflective coat needs to be there. Otherwise the interference doesn't occur. I doubt the surface of the film substrate itself is sufficiently reflective for this to happen and if the nature of the grains in typical B&W film is capable of this to begin with.

Don't let this stop you, though. It'd be interesting to see what you get. Please also share if this turns out to be a dead end street; it'd be relevant to record this as well. As you know, there's a massive confirmation bias in publication.

 

[Helge]

Yeah. But the nature of the substrate matters, as does the emulsion topology. Neither are geared towards this kind of interference pattern in regular film.



In the process of making a Lippman plate, AFAIK the reflective coat needs to be there. Otherwise the interference doesn't occur. I doubt the surface of the film substrate itself is sufficiently reflective for this to happen and if the nature of the grains in typical B&W film is capable of this to begin with.

Don't let this stop you, though. It'd be interesting to see what you get. Please also share if this turns out to be a dead end street; it'd be relevant to record this as well. As you know, there's a massive confirmation bias in publication.

Incidental and slight effects Koraks, could be good enough™. Should be enough to determine green from blue at least.

 

[Findlay]

Just made a quick scan:

https://wetransfer.com/downloads/d9d4b27f2c0a1ac6be8b53a10a337ed320231114114525/90496fc85723a190fefdb5f829b9954120231114114525/fc0de6

 

[Helge]

Just made a quick scan:

https://wetransfer.com/downloads/d9d4b27f2c0a1ac6be8b53a10a337ed320231114114525/90496fc85723a190fefdb5f829b9954120231114114525/fc0de6

That's very interesting!
So you are Batman. You should have no trouble doing this.
Have you considered that the AH backing can also work as faint colour filter?

 

[koraks]

Just made a quick scan:

https://wetransfer.com/downloads/d9d4b27f2c0a1ac6be8b53a10a337ed320231114114525/90496fc85723a190fefdb5f829b9954120231114114525/fc0de6

If you don't mind, here are both pages presented in a more accessible and more enduring way:

 

[koraks]

Btw, this process is conceptually quite similar to very early color film approaches such as Kinemacolor. While it evidently works, it's also based on rather pronounced/substantial filtering to differentiate hues. This is rather far removed from exceedingly more subtle signals such as the ones we've discussed so far in this thread. For a practical application (even with a very faint effect), I wonder if anything useful is really recorded on B&W film.

 

[Findlay]

That's very interesting!
So you are Batman. You should have no trouble doing this.
Have you considered that the AH backing can also work as faint colour filter?

That's a good point, although I was hoping to use it for older materials before the AH backing. Maybe not really old materials though as there needs to be some colour sensitisation I think.

 

[Findlay]

Btw, this process is conceptually quite similar to very early color film approaches such as Kinemacolor. While it evidently works, it's also based on rather pronounced/substantial filtering to differentiate hues. This is rather far removed from exceedingly more subtle signals such as the ones we've discussed so far in this thread. For a practical application (even with a very faint effect), I wonder if anything useful is really recorded on B&W film.

Maybe, but it also worked without filtering with subtle effects such as different film and even different lenses.