AmDi vs Brightness

[Tony]

I know this is a bit basic but I had tried this experiment and got me a thinkin.
I made a batch of DCG film last week and after a plate was coated I added some AmDi. I made like 4 plates adding one gram of AmDi to my batch.
The idea was to see a color shift.
Well long story short, the film was subjected to some higher than normal temperature due to a power outage and therefore was not too controlled.
I shot the film anyway, just a few plates here and there.
Indeed they were shifting bluer as the concentration went up. I never made it to BB.
But I wondered, why didn't they get brighter?
Should they have?
I did vary the fix time to maximize things.
Maybe being subjected to heat it killed the film a bit but even looking at past postings there is not much said about brightness and more AmDi except in going to BB which is brighter for a different reason. The film increases sensitivity, but nothing on brightness.
Wouldn't more AmDi mean more cross linking?

Lastly, this is a bit hard to describe but I will try.
Looking though some older plate I did I noticed some have a distinct hue to them. In areas where there is no object the film has a reddish chrome look. In other words it is where light (ref) passed through the plate but no object to reflect back. It has a red metallic hue. I cannot remember the exact formulation but is this seen with a higher concentration on AmDi?

Thanks,
Tony

[Johnfp]

I'll bite

Non hardened gelatin has and index of refraction of something
Optimally hardened gelatin has an index of refraction of something

If you have a bright hologram and the first IR is fixed and the second is pretty maxed out, then you really cant get a brighter hologram by doing anything. Maximum delta of index of refraction of the two is already at it's highest.

So if the second IR is not optimally hard (a weak hologram) then yes possibly, but there are many ways to get that light fringe at is max IR.

Make sense?

[Johnfp]

I aways go back to thinking about the process with the little voice in my head sayin, "you are not processing the exposed areas but the unexposed areas which makes me rethink things.

More AmDi in the hardened area means a little more shrinkage, the small percentage of added AmDi you put in.
More AmDi in the unhardened area does really nothing other then give the same % more shrinkage as the hardened are.
Thus a blue shift as the two fringes have shrunk but I dont see any more hardening due to the added AmDi.

It can probably be explained, although beyound my capacity, that for a certain volume of gelatin it only takes so much AmDi to fully crosslink the gelatin. Any more and you just have AmDi left over.

[Tony]

More AmDi in the unhardened area does really nothing other then give the same % more shrinkage as the hardened are.

More AmDi in the hardened area means a little more shrinkage, the small percentage of added AmDi you put in.
More AmDi in the unhardened area does really nothing other then give the same % more shrinkage as the hardened are.
Thus a blue shift as the two fringes have shrunk but I dont see any more hardening due to the added AmDi.

Thanks John,
I have more questions but the first is, then why do we pump as much AmDi until the brink of crystalization to make BB holograms?

So in managing the unharden area is mainly a function of fix (light, heat or chemical) and perhaps water rinse?

[Johnfp]

I never knew you had to saturate the gelatin with AmDi for a BB hologram. I thought it was more in the fast dehydration (heat and fast concentrations of Alcohol) then the amount of AmDi. To basically seal the outside first, push the water down and swell the inner fringes more then the outer fringes and then dry it that way.

[Tony]

I never knew you had to saturate the gelatin with AmDi for a BB hologram. I thought it was more in the fast dehydration (heat and fast concentrations of Alcohol) then the amount of AmDi. To basically seal the outside first, push the water down and swell the inner fringes more then the outer fringes and then dry it that way.

I always thought you needed higher concentrations for BB. Perhaps you need the film to be as crosslinked strong as possible to with stand the force of rapid dehydration.

[Dinesh]

I aways go back to thinking about the process with the little voice in my head sayin, "you are not processing the exposed areas but the unexposed areas which makes me rethink things.

Not so. You're processing them both. The fringe profile is ideally sinusoidal. This means that there is only a very small part of the fringe that is completely dark (no cross linking). As you go across a fringe, the fringe gets "brighter" and "brighter" (ie the fringe height increases), then gets lower and lower, then touches zero and raises again, like an AC signal. There is no clear-cut "dark" area, just as in an AC signal, there is no clear time of zero voltage. If the fringe profile were square, ie it gets to zero, stays at zero for a while, then abruptly rises to some value, stays there for a while and drops to zero again, then the lower part of the fringe profile would have no reduced chromium, hence no latent image and hence almost no development. The 'almost' is because there is always some development, even in the dark areas. This is the main reason for dark reaction.

By the way, don't you mean 'you're not processing the unexposed areas'? By 'processing' I assume you mean that you're enhancing an existing latent image. But, there's no latent image in the unexposed areas.

It can probably be explained, although beyound my capacity, that for a certain volume of gelatin it only takes so much AmDi to fully crosslink the gelatin. Any more and you just have AmDi left over.

Imagine you're standing on a raised platform. Below you is a large dance floor. On this floor there are many people with white hats and a few people with orange hats. Now, you throw table tennis balls onto the dance floor. If a white hatted person gets hit by a ball, then he/she must immediately grasp the hand of an orange hatted person. In the beginning, this is not easy; there are too few orange hatted people. As you add more orange hatted people, the white-hats find it easier to grab an orange hat. As you bring on more and more orange hats, there are going to be white hats that have their hands full and can no longer grasp orange hats' hands. There will be a lot of orange hatted people who are not "linked" to a white hat. Then a huge flood of water is gushed into the dance floor. All the orange hats who are not connected to a white hat get swept away by the flood.

[Johnfp]

Oh, second part, sorry.
If you read The Mechanics of gelatin and the DCG Process, the last section points out what I mean about processing the unexposed areas.

The unexposed area have very little crosslinking, some or you get that dang milky hologram. So since gelatin is soluble in water, then it only goes to reason that a lot of the gelatin gets lost with the washing process, well maybe not a lot but some. Then when drying in alcohol the unexposed area shinks more then the exposed area of the hologram from glass to surface.

So i try not to forget that when the DCG hologram is fully processed, we chemically do something (mostly) to the exposed areas but mechanically do something (mostly) to the unexposed areas.

So to answer:
Exposed area
AmDi and light - lots of crossliking and AmDi state change
Fixing - lots of crosslking
Water - just rinse out non used AmDi
Alcohol - just remove water from pretty rigid gelatin scaffolding

Unexposed area
AmDi and light - very slight crosslinking and very light AmDi state change
Fixing - very little additional crosslinking
Water - Rinsing out lots of AmDi as most was not used to crosslink and rinsing out uncrosslinked and non trapped gelatin strands.
Alcohol - remove water and gelatin shrinks significantly compared to exposed area