Maybe he can move my comment as well.
Kodachrome has a built in yellow colloidal silver filter
Wasn't there a built-in yellow filter behind the blue sensitive emulsion layer in Kodachrome? It was made out of colloidal silver, IIRC, which a a form of silver that is naturally yellow in color. Thus it would serve to filter out the blue photons from the red and green sensitive layers (since these layers are also sensitive to blue light).
Originally Posted by dmschnute
Apparently this colloidal silver layer is made out of metallic silver particles and not silver halide particles, else it would be fixed out in the hypo fixing bath. Since in normally processed Kodachrome the silver metal is bleached to ag+1 and then fixed, the colloidal silver is transformed into silver ions which will dissolve in hypo.
However, being colloidal, the silver metal particles might be very much smaller than typical grains and might be more susceptible to bleaching than the rest of the emulsion. Could a brief bleach selectively affect the colloidal silver only and not the image grains? Allowing just the yellow colloidal silver layer to be removed? Just asking if anyone knows.
There are instructions on Kodak's web site for bleaching this layer out.
Not trying to flog a deceased equine, but this thought popped in my head recently when I got back a roll of old Ektachrome E2 film that had been processed as B&W.
The company that did it said that it would be processed first as B&W and scanned. Then, if there were any recoverable images and a good chance of success, the roll would be further processed into color.
I truly do not know:
1) How this is possible if the color dyes (or what remains of them) are already in the emulsion
2) Is it possible that we could have our Kodachrome developed into a B&W and scanned *BUT* left in a state whereby if a viable process were to emerge in the future the film could still be converted into a color image, similar to what the company was going to do with my roll of Ektachrome E2?
Somehow I doubt that we could, but I am by no means well versed enough to figure this out. I did search the forum for an answer and was unable to locate one. P.E.-- out of curiosity, do you happen to know if this is possible?
What you describe is possible with Ektachrome type films if it is not fixed after the B&W development, but not possible with Kodachrome type films. (one exception here though - the film must be unfixed and kept dark until that process comes along)
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Yellow filter layer of Kodachrome
Thanks to PE and his tip concerning how to bleach out the yellow filter layer in Kodachrome. Of course this layer is bleached and fixed out when Kodachrome is developed into color images, and presumably when Kodachrome is developed as a Black and White reversal. But the yellow layer remains when Kodachrome is developed as a Black and White negative.
Kodak published a document TECHNICAL DATA/COLOR FILMS in April 1999 which gave instructions on removing the yellow layer. It is called "Printing Color Films Developed as Black-and-White" and can be found on the internet at
This yellow layer is composed of colloidal silver; that is silver grains so small that they can go into colloidal suspension. At this small size they interact more directly with light rays, apparently absorbing blue light more efficiently and thus appear yellow.
The instructions that Kodak gives are simply to mix 1 oz, 28 grams, of anhydrous citric acid into one gallon of Kodak Rapid Fixer which has been mixed to the proper concentration to fix films. The Kodachrome photos are fixed in this for 7-14 minutes at 75-80 degrees f, after having been soaked in Photo-flow and rinsed. The ingredients for Rapid Fixer can be found at https://www2.itap.purdue.edu/msds/docs/9712.pdf
The main ingredients for the Rapid Fixer are: ammonium thiosulfate, sodium acetate, boric acid, sodium bisulfite, aluminum sulfate and sulfuric acid. The ph of this material must be low. The sulfuric acid probably has enough potential to oxidize the colloidal silver particles, especially since these are so small. I'm guessing that these will be oxidized first and then fixed out by the thiosulfate. The instructions do warn that this Rapid Fixer can reduce the metallic silver forming the image.
I'm guessing also that the citric acid provide citrate ions causing the yellow silver to form silver citrate. Perhaps this salt is less soluble than the acetate salts and will isolate the silver atoms and drive the reaction to dissolve out the colloidal silver. Would these citrate salts be less soluble?
Kodachrome as B&W Neg
Originally Posted by falotico
Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1, 5DmkII / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic | Sent w/ iPhone using Tapatalk
I don't know why the internet address did not print out correctly in the above post. Sorry.
My apologies again. I definitely am NOT posting blank posts, but I seem to have stumbled into a computer syntax error with this web address. If you can read it then copy it and paste it into the address line at google. Then click on the item "Printing Color Films as Black and White". This should bring up the Kodak document. The web address reads out in longhand as: www dot kodak dot com backslash global backslash en backslash consumer backslash products backslash pdf ae31 dot pdf
Otherwise, try a google search for the title of the Kodak document, "Printing Color Films Developed as Black-and-White". Hope it works!