Archived posting to the Leica Users Group, 2001/11/17

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Subject: Re: [Leica] 'chrome stability
From: "C.L.Zeni" <clzeni@mindspring.com>
Date: Sat, 17 Nov 2001 20:12:57 -0500
References: <5.1.0.14.2.20011117153341.00a962a0@pop.mindspring.com>

At 05:57 PM 11/17/2001, you wrote:
> > Question:  I've always understood that the major difference between
> > Kodachrome and E4/6 is that the latter carries the dyes in the
>emulsion,
> > and that Kodachrome has the dyes added at processing.  IF (big if...)
>this
> > is the case, why would environmental conditions experienced by the
>film
> > prior to processing have any effect on the color?
> >
>It is the "dye couplers" not the dyes which are in the chemistry.

Yes, you're right.  A sniff thru Google turned up the following link 
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000aqm:
and scroll down:

Kodachrome is unique in that the color couplers are in the color developing 
processing solutions.  Ektachromes (and other manufacturers' chromes) have 
the couplers coated into the corresponding films layers; cyan in red 
sensitive layer, magenta in green sensitive layer, and yellow in blue 
sensitive layer.

Kodachrome process is a wonder to behold.  There are four developers and 
two re-exposures to light.

K-14 First Developer brings up the negative black and white image in the 
silver (E-6 also has a B&W first developer).

After K-14 first developer,  the film is next  exposed during 
processing  to pure red light, through the base-side of the film, closest 
to the bottom red-sensitive emulsion layer.  This exposes the remaining 
undeveloped  red-light-sensitive silver halide to provide a reverse 
(positive) image.

The next developer is the Cyan developer.  In K14, each color developer has 
a unique developing agent which only couples with the freshly "re-exposed" 
layer.  hence, you get a "positive" dye-cloud image in the proper layer 
when processed in the proper sequence.

Third, the film is re- exposed in-process to pure blue light, through the 
emulsion-side of the film, closest to the top blue-sensitive layer.  This 
reverses the blue-sensitive silver halide.  The next developer is Yellow, 
which works like the cyan described above, but with a different developing 
agent, and of course Yellow dye-coupler.

Fourth, the film goes directly into the Magenta developer.  It is not 
re-exposed to green  light.  Instead, there is a chemical fogging agent 
which "fogs" any undeveloped silver halide in the film.  By this point, the 
only silver halide is in the green sensitive layer, because all the other 
layers have had both negative silver developed, and the reversed 
silver-halide developed into dye clouds.  So the green-sensitive layer is 
chemically reversed, and the Magenta coupler-containing developer goes to 
work on whatever silver halide remains.

Then the rest of theK-14 process is like modern color film "tail" 
solutions.  Bleach the developed silver back to the silver-halide 
state.  Fix the silver-halide into solution out of the film.  And an 
assortment of washes in between.  Fourteen steps in K-14 leave you with a 
dye-cloud image.

E-6 has a First Developer and only one Color Developer which develops the 
couplers coated into the specific layer structure of the film.

I get a thrill just thinking about the complexity of K-14.  When it is done 
properly, the results are truly stunning!
- -- Dan Sapper  (Rochester, New York, USA), September 13, 1999; 02:36 A.M. 
Eastern

But again, it appears that the color isn't added until processing, so my 
wondering remains... :)

- --
Craig Zeni - REPLY TO -->> clzeni at mindspring dot com
http://www.trainweb.org/zeniphotos/zenihome.html
http://www.mindspring.com/~clzeni/index.html

In dog years, I'm dead.

- --
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Replies: Reply from "George Weir" <george@georgeweir.com> (Re: [Leica] 'chrome stability)
In reply to: Message from "C.L.Zeni" <clzeni@mindspring.com> (Re: [Leica] 'chrome stability)