-- A sinister little midget with a bucket and a mop / Where the blood goes down the drain --
Film as you described it:
Originally Posted by Photo Engineer
Sensitivity => dye layer result
200 Blue => yellow pumpkin
300 Green => magenta grape
400 Red => cyan cyan!
[BASE LAYER, not water permeable]
I take it that
1: a yellow filter layer must be underneath the blue emulsion, so that any blue light which make it past the Blue-sensitive layer can't activate silver particles in the Green-sensitive and Red-sensitive layers...because ALL silver halides are ALWAYS sensitive to UV and blue light..
Which gives us an actual structure like this:
Sensitivity => dye layer result
200 Blue => yellow pumpkin
[Yellow filter, not stated, to protect lower layers from blue light]
300 Blue + Green => magenta grape
400 Blue + Red => cyan cyan!
[BASE LAYER not water permeable]
2. Yellow came out as pumpkin due to that area of the negative being contaminated with dye formation in the magenta-producing layer.
Dynamic at work. Developer flows THROUGH the layers, starting at the top, and works its way towards the bottom layer of the film...and this effect is strongest as the developer first hits a layer, before the layer beneath it is wet... so there's really strong developer activity, producing lots of oxidized developer..but because the layer below it is still dry, a significant amount of the developer that is oxidized in the first few seconds with the top layer end up migrating deeper into the film [green layer producing magenta dye] before hitting a dye coupler. And while this isn't the majority of the developer oxidized in the yellow layer, its enough to change what should be an area of the negative with only yellow dye into one that has lots of yellow dye PLUS enough magenta to screw up our colors.
Similarly, with the magenta-producing layer... as the fresh developer first works its way the magenta layer, there is still overall drift of the water molecules through the gelatin to drag oxidized developer from the magenta-producing layer down into the cyan-producing layer, thus yielding "grape". Next, even after the magenta-producing layer is water saturated, this drift-induced effect continues because water is STILL migrating into the cyan-producing layer..
Lastly, in the bottom (cyan-producing) layer, there is no color distortion because as some oxidized developer makes its way down to the film base, well, now it's deep within the cyan-producing layer, and will have to travel all the way up to the top of the cyan-producing layer before it can possibly meet up with a dye coupler from the wrong layer...and by the time such a thing could happen, there is no longer any net directional drift of water + developer + oxidized developer through the layers, and so the oxidized developer molecules at that point
I'm assuming that after the initial water "front" reaches the film base, the effect of net drift of water + chemistry ceases to have much effect.
Diffusion of oxidized color developer is in a sphere around the site of development. The lifetime of the oxidized color developer is longer than the diffusion rate into or through more than one layer. Thus, all colors will remain contaminated.
The solution you suggest is therefore not viable. The correct solution is to add an oxidized developer scavenger to either the film or the color developer. Sulfite might work just fine, but it can vary in concentration due to aerial oxidation. Therefore it is best to add an antioxidant to the film, in the interlayers.
Any suggestions on modification now?
I didn't know I suggested a solution :-) I was just trying to see if I understood the actual problem, and the dynamics which caused it.. which you confirm IS an issue, but not for the specific problem you presented. Thanks for the explanation of oxidized developer scavangers...that would have probably eluded me for a long time.
I had heard that color film actually consisted of a dozen layers or more, but before reading this thread, I never understood why. Now I do, especially with your mention of oxidized developer scavangers in interlayers.
I have no constructive input to this conversation; only wonderment. I'm trying to wrap my mind around the enormity of a machine that would apply a dozen layers of emulsion on the film base. I can only conclude that the master roll goes through multiple passes, drying, and re-rolling on the machinery, that it is not done in a single pass, or the machine would be a mile long. I also wonder if the liquid emulsion is applied by rollers like a printing press, or if the base is run through the machine with a bead of liquid, whose viscosity is carefully controlled to draw ann appropriate amount of liquid out of the bead, hence controlling thickness of the emulsion layer.
I also wonder how long of a distance must the wet film travel before it is hardened enough to roll on the other end.
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I typically "ignore" reading about color, I like B&W so much more.
But although I know I have a long straight line, and I have seen graphs and overlapping curves to build that straight line. For some reason I hadn't been thinking of it as three different speed emulsions like 200, 25 and 3
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
Bob's book is certainly a great way to learn about making film. I recommend it.
Basically, up to 12 or more layers are coated at one time using one slide or curtain coating hopper. These layers all go through nearly one mile of high speed drying and the coatings are made on mile long (or longer) rolls that are up to 72" wide.
No need to answer, as I don't want to clutter the thread. I'll not be buying any book because I live hand to mouth as it is. I'm trying to picture in my mind a very long conveyor with conductuion rollers that can only make contact with the backside of the film. Obviously, if the film is wet, then no rollers can ride on the emulsion side. Unless the machines are built where any tires on the front side are all aligned, and there are several sacrificial strips along the width of the roll, that are slit out later and thrown away.
Last edited by Tom1956; 06-28-2013 at 01:58 PM. Click to view previous post history.