Color filters in interlayers in color negative film

[koraks]

{Moderator note: this thread was split off from another one here: https://www.photrio.com/forum/threads/kodak-planning-to-replace-remjet-on-vision-3-films.213976/}

As far as i know color films do have several filter layers which are needed for exposure, but for printing/projection...

Two color filters; a minus blue (=yellow) beneath the blue-sensitive, top image forming layer, and a minus-green filter between the red-sensitive and the green-sensitive layers. The yellow filter can either be a dye or Carey Lea silver. I don't know for sure which is used by Kodak in Vision3. The green filter AFAIK is a dye. It's possible that this contributes to the color of the wash water. However, I'd like to note that the same magenta color also washes out of e.g. Kodak double-X, which evidently doesn't involve these color filter layers.

 

[Harry Callahan]

I see. To wash out with water these filter layers had to be water-soluble and this could be problematic for film storage before development. I think there was an Agfa color film in the 60s which had water-soluble dyes or couplers - and this film couldn`t stand high humidity before development. Therefore it was better to have the filter layers not water-soluble.

 

[koraks]

I think there was an Agfa color film in the 60s which had water-soluble dyes or couplers

Filter dyes would have been water-soluble. Dye couplers to the best of my knowledge have always been hydrophobic.

Therefore it was better to have the filter layers not water-soluble.

The color filters in the interlayers need to wash out for the negatives to work as negatives. You need to enlarger/scan them, after all. So this filtering needs to be gone from the processed negative by design.

 

[Harry Callahan]

Yes, they need to wash out during development but maybe they are not soluble to pure water.

 

[koraks]

Yes, they need to wash out during development but maybe they are not soluble to pure water.

I see the magenta stuff wash out in a regular final wash in plain tap water. It's faster in alkaline water which may be due to the nature of the dyes and/or the permeability of the emulsion. I lean towards the latter because basically anything washes out of a gelatin emulsion faster at high pH.

 

[jmrochester]

Yes, they need to wash out during development but maybe they are not soluble to pure water.

Carey Lea Silver utilized in some yellow filter layers is an example of a water-insoluble material that is solubilized by processing chemistry. Filter dyes are generally not water soluble -- at least in color films.

 

[jmrochester]

So they remain in the film after processing?

No, they're solubilized by processing chemistry. Calling them "dyes" is a misnomer (of which I was guilty above ).

 

[Harry Callahan]

Carey Lea Silver utilized in some yellow filter layers is an example of a water-insoluble material that is solubilized by processing chemistry. Filter dyes are generally not water soluble -- at least in color films.

That was my idea. This also makes color film more resistant to higher humidity before processing.

 

[koraks]

No, they're solubilized by processing chemistry. Calling them "dyes" is a misnomer (of which I was guilty above ).

But the chemistry is a watery solution...
I understand that the yellow filter if it's Carey Lea will bleach & fix out, but the other filter will work differently.

 

[jmrochester]

But the chemistry is a watery solution...
I understand that the yellow filter if it's Carey Lea will bleach & fix out, but the other filter will work differently.

We're getting far afield from the original topic. How do you know what -- if anything -- is in the other interlayer?

 

[koraks]

How do you know what -- if anything -- is in the other interlayer?

There are several things there, including a color filter to prevent the cyan forming later to respond to geen light. Blue is already dealt with higher up in the stack. In color paper its different because there is the inherent difference in speed (and an increase order to the layers). But in film there's no such luxury so there has to be a magenta filter. you can find this in some documentation esp in the motion picture domain. E.g. https://www.imaging.org/common/uploaded files/pdfs/Papers/2006/ICIS-0-736/33687.pdf

 

[jmrochester]

There are several things there, including a color filter to prevent the cyan forming later to respond to geen light. Blue is already dealt with higher up in the stack. In color paper its different because there is the inherent difference in speed (and an increase order to the layers). But in film there's no such luxury so there has to be a magenta filter. you can find this in some documentation esp in the motion picture domain. E.g. https://www.imaging.org/common/uploaded files/pdfs/Papers/2006/ICIS-0-736/33687.pdf

The answer to your concern is in the fine print of that document. I'll leave it there.

 

[Lachlan Young]

The interlayers contain scavengers to stop what the document describes as 'crosstalk'.

The solid particle filter characteristics (and how they stay in place for coating and are removed at processing) can be found in some other EK patents.

 

[koraks]

The answer to your concern is in the fine print of that document. I'll leave it there.

The solid particle filter characteristics (and how they stay in place for coating and are removed at processing) can be found in some other EK patents.

...and then what is the nature of these 'solid particles' and how do they disappear from the film during processing?
Is there a particular reason to be restrictive on speaking up about what you know? It's not like this is top secret information.

Of course there's this from al already quite old patent (US2391198A):

The intermediate layer may also contain a dye, such as a filter dye, which is uniformly removable in the developer, provided it contains no dye bleachable under the influence of a silver or silver salt image.

And this (US3765893):

To produce the individual partial color images,
the differently sensitized silver halide emulsion layers
are usually separated from one another by gelatin inter
mediate layers which can, if desired also contain filter
dyes.

The interlayers contain scavengers to stop what the document describes as 'crosstalk'.

Sure; they're part of the interlayers in color paper, too.

 

[koraks]

We're getting far afield from the original topic.

It's no longer a problem; I've separated this discussion from the original thread. Please don't hold back in sharing what you know.

 

[Lachlan Young]

what is the nature of these 'solid particles' and how do they disappear from the film during processing

Essentially that they do not solubilise or wander at coating pH (without needing the use of a mordant) but are readily solubilised at processing pH.

The patents attributed to Diehl and Factor (et al) give quite a lot of detail, synthesis routes etc.

 

[Rudeofus]

Essentially that they do not solubilise or wander at coating pH (without needing the use of a mordant) but are readily solubilised at processing pH.

Could this be a possible reason, why ECN-2 still asks for a Sulfuric Acid stop bath? Or can we safely assume, that all filter dyes are designed to dissolve at alkaline pH?

PS: at least the filter dyes used to fine tune emulsion sensitivity across the spectrum definitely do wash out with tap water.

 

[koraks]

Could this be a possible reason, why ECN-2 still asks for a Sulfuric Acid stop bath?

All I can say is that Vision3 processes just fine in acetic acid. The explanation @Photo Engineer used to give for the sulfuric acid was just to pull the developer out of the game as quickly as possible.

 

[Lachlan Young]

Could this be a possible reason, why ECN-2 still asks for a Sulfuric Acid stop bath? Or can we safely assume, that all filter dyes are designed to dissolve at alkaline pH?

PS: at least the filter dyes used to fine tune emulsion sensitivity across the spectrum definitely do wash out with tap water.

Coating pH is around 4-6 according to the patents - and they describe tests (including washing) to demonstrate that only under conditions of around pH 8 or greater do the solid particle filters solubilise.

EP0323729B1 and others from the same team are worth a look. Seems like the basic work was done in the earlier 1980s but it took a decade or so to fully productionise them.

 

[lamerko]

As far as I know, "Carey Lea silver" is only used in Ektachrome by Kodak, and in the past also in Kodachrome. There is a valuable document - "AE-31". There Kodak describes non-standard techniques - including a little-known method for removing remjet from Kodachrome, as well as removing the colloidal layer. By the way, there Kodak describes it simply as "stain".