Color System Engineering II

[rowland_mowrey]

This will contiune approximately from where the last thread left

off. First though, I want to answer a few questions and make a few

comments.

 

1. For those that want to know more about coating and emulsion

making, go to Jim Brownings page here:

http://www.dyetransfer.org/images/DyeTran.pdf

 

Or see the pictures of emulsion making and coating at EK in George

Eaton's book referenced elsewhere by me.

 

2. For those of you that don't know what latitude is, or what a dye

curve is or what ISO or EI or ASA speed are or what a coupler is, I

suggest you read the introductory or learning pages on this site.

They have a lot of information. Most of the rest of you know what

I'm talking about when I mention those things. However, don't be

discouraged from writing me if I make things unclear, or leave things

out or bring up something entirely new to you. I'll either answer

the question or point you in the right direction to get an answer.

 

3. As Joe Manthey pointed out, there are newer methods for designing

film, but I'm starting with basics, not leaping into modern

techniques right off. I'm starting just like Mannes and Godowsky or

Vittum and Hanson did 70 years or so ago. I am disclosing no

proprietary information. And, there are others more qualified than me

to speak on these subjects. I agree.

 

With that said, let me continue from where we were before. We made a

3 layer coating of yellow/magenta/cyan layers with 9 emulsions to get

the proper latitude, and we got muddy colors. The cyan layer was low

in contrast, the magenta next lowest, and the yellow looked almost

right. What happened? The single layer coatings were fine.

 

Well, lots of things went wrong. Here are some of them listed out

for you.

 

1. Color developer wandered between each layer so that oxidized

color developer in the magenta layer intended to make magenta dye,

diffused outward in a sphere and made cyan and yellow dye as well,

thereby muddying up the color.

 

2. Blue light exposed the top layer, blue and green light exposed

the magenta layer (but we only wanted green light to expose it) and

blue, green and red light exposed the bottom layer when only red

should have.

 

3. Light that got through all 3 layers bounced off of the film

support as if it were a mirror and then began bouncing back and forth

in the film reducing sharpness and increasing crosstalk.

 

4. The pH and color developing agent diffusing into the coating were

consumed layer wise and proportinately less and less alkali and color

developing agent were available to each lower layer thereby reducing

contrast layer wise. In other words, the developer was formulated

wrong, and the coating was formulated wrong for the conditions of the

coating and test.

 

5. Each layer, as it started developing, released a wave front of

acid and halide ion (mixed bromide and iodide in this case). The drop

in pH and the flood of halide ion restrainer slowed down the

development rate of each lower layer. Again this is a coating and

developer issue both. It might even involve agitation and time of

development.

 

Well, there is a short list of items that didn't address some other

major issues such as inherent sharpness of the coating. With all of

those multiple internal reflections, the sharpness of this coating at

this point is meaningless.

 

Lets start first with the fact that all colors of light went through

the coating when we just wanted to expose the top to blue, the next

to green, and the last to red. How do we fix that? Well, we can add

a yellow filter dye layer under the blue sensitive layer. Here is

our new coating: yellow/dye layer/magenta/cyan/support.

 

Testing will show a vast improvement in yellow and magenta dye, but

diffusion is slower due to the extra layer so magenta and cyan

contrast is lower, and there is green light getting into the red

sensitive bottom layer. Also, we find that within a week of making

the coating, the yellow dye has diffused out of the interlayer and is

evenly distributed throughout the coating making it useless. So, we

try mordanting the dye in place to hold it in the interlayer.

 

Well, this works just as well, in fact even better. It turned out

that the yellow dye in the interlayer was diffusing even during

coating and lowering its effectiveness. However, now when we process

the film, the yellow dye stays in the coating and leaves a yellow

stain. Back to the drawing board.

 

This time, we coat finely divided yellow silver in the interlayer.

This is called CLS (Carey Lea Silver) for the inventor, and is so

finely divided it is yellow in color. Now when we process the

coating, everything works right. The yellow silver absorbs the blue

light and the yellow silver stays in place with keeping. In

addition, the bleach and fix remove it and leave a clean d-min.

 

We stil have some yellow dye formed as a fuction of magenta layer

silver development, and lots of cyan dye as a function of magenta

layer silver development. We also have magenta dye formed as a

function of cyan layer silver development. So, we come up with a new

coating as follows: yellow/CLS/magenta/gelatin/cyan/support.

 

Now when we develop, we see a bigger improvement in the color. There

is less contamination, but there is still enough that the colors are

degraded. What should be our next step?

 

We can leave that 'till next time, provided you are interested. Oh,

for those interested in developers, I'm going to try to solve

problems in the coating first rather than the developer which I will

get into later on in this series (if we ever get that far).

 

The response on the previous thread was sparse, but the e-mail was

pretty good so I decided to keep forging ahead. Give me feedback if

you want to continue, either on this thread or by e-mail.

 

Ron Mowrey

[James G. Dainis]

Highly informative, as usual. I'm curious about one thing. Why do faster films have larger grain? I should think a finer or smaller grain would be more sensitive to low light.

[rowland_mowrey]

James;

 

It is the cross section to light presented by the crystal that partially determines its light sensitivity. It requires 3 hits of photons to render a sensitivity speck on a grain developable. If the grain is too small the probability of 3 photons hitting a grain decrease.

 

With the newest EK technology 2 hits will do it.

 

That is a simplification, but basically represents the reasoning behind T-grain technology. The huge cross section and thin grain allows a lot of hits per grain and even allows light to go through the grain and hit grains behind them. K grains OTOH, can be hit by light and absorb it completely due to their thickness.

 

Ron Mowrey

[phil_erickson]

Please continue! Learning is always a worthy pursuit..

 

cheers.

[jan_brittenson]

So how does Fuji manage to make the grain in their 100F transparency films affect mainly luminance, while just about every color neg and many other transparency films have a highly conspicuous chromatic speckle? The 100F films looks almost crystalline at magnification while just about all other color films, pos or neg, are chromatic. Heck, the grain in Astia 100F (RMS 7, FWIW) shows far less than NPS (RMS 4)!

[grahams]

"As Joe Manthey pointed out, there are newer methods for designing film, but I'm starting with basics, not leaping into modern techniques right off"

 

Lets keep it simple, huh...

[cole_petersburg]

Ron, will you sell me your film when Kodak discontinues theirs? :)

[rowland_mowrey]

Cole;

 

You probably have already used some of 'mine'. I helped design the first Kodacolor Gold 400.

 

Jan;

 

I have no clue what you are talking about. Could you elaborate please? Thanks.

 

Ron Mowrey

[jan_brittenson]

Have you ever examine Fuji 100F films closely for grain? You'll keep looking for it, closer and closer, but it's actually not that small. It's just really difficult to see because it's virtually free from chroma.

[rowland_mowrey]

Jan;

 

Under normal conditions, the sharpness of a given dye cloud can be related to the sharpness of an image. If the color spots or grains are more diffuse, there have to be more of them to reach the same density level, therefore they form further away from the silver that caused them to be formed, and therefore the image is more diffuse or less sharp.

 

That is one answer, but if Fuji is as sharp as other films, then it could be that they have also increased contrast while making the dye density more diffuse. This would have the appearance of increasing sharpness.

 

Another possible answer is that they might be using an extremely fine grained emulsion which has unexpectedly high speed. Then they coat a higher level of silver. For each grain, they get less dye, but there are more dye spots so the same density and contrast is achieved. This would require a new invention.

 

More coupler dispersion particles in a layer with a competing coupler would also cause this effect by lowering density of a given dye particle but create more of them in the area. This may or may not affect sharpness depending on how it was done.

 

Using a water soluable, but ballasted coupler would have this effect. Then there would be no coupler droplets from the dispersion, but there would be small 'micells' of coupler or small aggregates with coupler and gelatin molecules in association. In this case, the coupler would affect coating properties and make coating the film far more difficult due to an area of science called 'rheology'. I doubt that they would use this method unless they have a viscosity modifier in the coating. This would also require an invention IMHO.

 

The use of a new coupler solvent with a different index of refraction could have this effect. This would require an invention.

 

The use of a coupler that is polymerized with gelatin or is a polymer itslef could have this effect. This would also probably impact on viscosity. This would require an invention.

 

It could even be a little bit of each of the above.

 

Those are a few ways OTOMH to do what you seem to observe. A few others are trickling through my head as well. If any make sense in this context, I'll post them as well.

 

Note to Fuji and EK researchers: These were not gratuitous suggestions. I expect my name to be on the patent if you decide to pursue any of my ideas. :-D

 

In the final analysis, it could also be an optical delusion. ;-)

 

Ron Mowrey

[scott_eaton]

Fuji slide films tend to sacrifice density range for a decrease in appearent grain as Ron suspects. Measure Reala vs Gold 100 sometime, or EPP vs Provia.

 

It doesn't explain how Fuji emulsions are able to reproduce far greater degrees of color saturation without blocking up or distorting colors like Kodak emulsions do - even comparing films in the same gamma range. You can fiddle with dye coupler engineering all you want. If it simply produces another legacy Kodak film with the dymanics of what they've been making for the past 20 years, nobody will buy it.