Archived posting to the Leica Users Group, 2001/11/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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. - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html