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narigas2006
02-26-2007, 06:52 PM
Hi All,

I was just thinking the other day, if there was a way to prepare an emulsion that is very slow to develop and fix, maybe using a prehardened and a non-hardened one (as I think paraformaldehide cross-link the gelatin protein and make it less permeable to the developer), then, one could coat the film with the hardened, dry, the recoat with the non hardened. The hardened would be sensitised to e.g Red and the non-hardened to green, then:

develop (short)
fix (short)
tone (in red) and bleach (ultra short)

then, hopefully, the hardened emulsion would be undeveloped,

then, redevelop, fix and tone (green) and bleach.

does it make sense or I am just hallucinating.

Alternatively, with the sensitised emulsion, coat 2 sides of the film (side A with red and side B with green) but that I think it would not work as the halide is opaque, unless the coating is extremely thin... Anyway, just thoughts!

cheers

richardson

PHOTOTONE
02-27-2007, 11:17 AM
While I can't comment on the technical side of the emulsion making, I can add that the two-color cine processes that were used in the 1920's up through mid-1930's did not use red and green dyes to form the final positive image, rather they used a cyan and a sort of peach color (IIRC), as the goal was to get natural looking flesh tones, with the other colors kinda falling where they may. Some colors looked right, others looked way off, but in general the effect produced an image that was mostly pleasing.

Photo Engineer
02-27-2007, 03:56 PM
The original Kodachrome used a selective development and bleach process similar to what you describe, but the use of a differential hardening scheme may not be feasible due to the properties of the hardening agents which diffuse rather more rapidly than they harden.

PE

htmlguru4242
02-27-2007, 04:27 PM
Interesting idea, I've though of trying to figure something like this out.

Purely out of curiosity, PE, how did the original Kodachrome work?

Photo Engineer
02-27-2007, 05:04 PM
Original Kodachrome was two color. The three color was something like this.

MQ developer to get negative in all 3 layers.
Reexpose film.
Develop in cyan developer.
Bleach dye in top 2 layers leaving cyan in bottom red layer.
Redevelop in magenta developer
Bleach dye in top layer leaving cyan in bottom and magenta in middle green.
Redevelop in yellow developer leaving yellow dye in blue layer.
bleach
fix

This leaves out many many wash steps.

The process was about 75 deg F, and took over 2.5 hours.

PE

Photo Engineer
02-27-2007, 05:06 PM
The current Kodachrome is like this:

MQ developer to get negatives in all 3 layers.
Expose back of film to red light.
Cyan develop.
Expose front to blue light
Yellow develop.
Chemical fogging bath
Magenta developer
Bleach
Fix

This also omits all of the many wash steps. The process is at 85 deg F and takes about 1.5 hours. See the patent for details.

PE

htmlguru4242
02-27-2007, 06:42 PM
With the original selective bleach process, how did they bleach dyes from some layers and not others?

Photo Engineer
02-27-2007, 07:39 PM
All color processes are diffusion limited or controlled. The process took advantage of a moving front of dye destroying chemicals.

It was very precise, down to the exact micron.

PE