Black and White Films With Two Emulsions

john_s

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From a Crawley article that I've posted here previously, talking about the new (as it was then) Delta 400 a comment about four emulsions being in D3200 if I'm reading it correctly:

<start of quote>
With the launch of Delta 3200 last year, Ilford came up with a
solution to the problem, evolved from 100 Delta. The same
principle is applied in the new Delta 400 reviewed here. In fact it
harks back to traditional know-how but in an updated guise. Delta
3200 is a bi-pack, and each of the two layers is made up of two
emulsions, four in all, of which three are new. The high-tech
halide crystals have a silver iodide rich core around which is the
bromide shell and sensitisers. The interfacing of the iodide rich
core with the bromide shell creates a larger number of possible
latent image centres in the shell to trap the incident light. So there
is enhanced sensitivity and pushability.
 
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Andrew O'Neill

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Wow four layers! I had no idea.
 

DREW WILEY

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Tri-X 320 sheet film is different from TX400 roll film, but in just how many respects I cannot say.
 

laser

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I'll comment on multi-layer B&W films. The use of multilayers is more about product sensitometric control than having multilayers to improve the resulting image. It is easier to achieve the desired sensitometry (speed, contrast, curve shape, fog) with two layers than one. Kodak had very small tolerances on sensi. In order to comply with requirements two layers and blended emulsions were used. The goal is to only production coat materials that will result in film that can be sold. To achieve this pre-product tests are run and materials are coated narrow to confirm their performance. Then the materials are coated on production equipment. One master roll is coated. Then the equipment is stopped. The materials are held in the tanks and delivery systems. During this "assessment stop" samples of coated film are sensitometricly exposed and developed in a fine tuned hardening developing system. Based on the assessment results, the re-start coating can be fine tuned so the subsequently coated film will satisfy the most stringent requirement. Having multi-layers gives more control tools to the engineers. Part of the task in designing films is to provide control tools that are necessary to compensate for any variations. The materials also have to be stable so they can withstand a few hours of "hold time" Without control tools waste and costs would increase. The pre-assessment roll may be sold if it is in release tolerances or it may be discarded if it is not within the tight tolerances.

If the coating order requires multiple master rolls then an end-test strip is taken after each master roll that goes through the same testing to confirm performance. Coating continues during the testing.


I'll also mention that during that the hay day of film, 1960 to 2003, the use of production coating time was carefully guarded. One of Kodak's challenges was making enough film on the multiple film coating machine scattered around the World. Production coating time (manufacturing capacity) couldn't be "wasted" making film that was not salable.

www.makingKODAKfilm.com
 

lamerko

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laser said:
From Shanebrook, "Making KODAK Film", 1st Edition . Figure 3, page 8.
Click to expand...

Thanks for the clarification. I had saved the picture but forgot to save from where. I take notes on such resources, but…
 

laser

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MTGseattle said:
Andy, are you headed down an interesting chemistry route?

Also, how long have film "curves" been available as a data point?
Click to expand...

Hurter and Driffield 1875ish
 

Steve Goldstein

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It's interesting that the emulsion layer thicknesses for FP4 and HP5 differ for 35mm, rollfilm, and sheet film.

And also that they write "rollfilm" (no space) and "sheet film" (space).
 

DREW WILEY

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HP5 sheet film has been coated on polyester base for a long time, not triacetate; and it isn't gray. That seems to be the case with all Ilford sheet films. A tinted base would be more characteristic of roll film, which the diagram oddly lists as clear. So I wonder if there are other errors on that posted diagram. HP5 has also undergone certain subtle emulsion improvements over the years, only one of which was formally designated as HP5 Plus.
 
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Milpool

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Panatomic-X had a special hidden third layer which is what made it the most awesome film ever in the history of everything.
 
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Andrew O'Neill

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Milpool said:
Panatomic-X had a special hidden third layer which is what made it the most awesome film ever in the history of everything.
Click to expand...

I wonder what this third layer was? I heard that this film contained Cadmium. I still have a box of 4x5, that I cracked open a couple of years ago, to compare with TMX 4x5. I was surprised at how well such an old film looked brand spanking new after processing. Could this special hidden third layer have something to do with this?
 

Milpool

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I doubt it because I made that all up.

But it’s interesting how well very old Pan-X seems to hold up based on peoples’ reported experiences. It doesn’t hurt that it was a slow film, but I’d still have expected fog /reduced sensitivity depending on how old it is.
 
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Andrew O'Neill

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It also had extended red sensitivity, much more than say, Delta 400, which I have always found intriguing, but have yet to exploit that...
 

Sirius Glass

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If I remember correctly Kodak Verichrome Pan was a two layer film with each layer having its own ISO. That allowed simple box cameras such as the Kodak Brownie Hawkeye to take photographs over a wide range of lighting, and that allowed box cameras to be practical and useful.
 

John Wiegerink

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Yes, that's what my dad used in his Kodak Target Six-16 box camera. What I'm trying to remember is if there was a Verichrome B&W film before VerichromePan B&W came out. I used to shoot VerichromePan in my Hasselblad 500C and develop it in Microdol-X or maybe it was plan Microdol. This old brain doesn't remember as well as it once did. Anyway, those negatives printed very nicely and seemed to hold the highlights from going into never, never land.
 

MattKing

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Early Verichrome Pan featured such multiple speed emulsions.
At the end, it was essentially Plus-X emulsion coated with less effective anti-halation tools.
 

Sirius Glass

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Before Kodak Verichrome Pan there was a Kodak Verichrome, but I never used it. I read about it, so the information is still available if you want it.
 

Ian Grant

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Sirius Glass said:
Before Kodak Verichrome Pan there was a Kodak Verichrome, but I never used it. I read about it, so the information is still available if you want it.
Click to expand...

The Verichrome trade name predates its use by Kodak by a number of years, in fact it was a Wratten & Wainwright plate emulsion along with Allochrome and Wratten Panchromatic introduced around 1907/8. The original Verichrome was not Orthochromatic but along with Allochrome although not fully Panchromatic needed the same Wratten safelight as their Panchromatic plates.

I was talking to a member here last year who had a box of Verichrome plates, he thought from the 1930s, however George Eastman bought Wratten around 1912/3. After Mees & Sheppard moved to Rochester to found the Kodak Research facilities Kodak Ltd continued selling Wratten plates made by their Wratten division until around 1920/1.

Later 1931 Verichrome film-pack & roll film was Orthochromatic.

Ian
 
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