Color stabilizer and the function of formaldehyde

Discussion in 'Film and Processing' started by greg_miller|10, Nov 2, 2011.

  1. Most effective final rinses/stabilizers in the past contained Formaldehyde. If doing a rewash on vintage reversal films (Kodachrome/Ektachrome) how important is it to restabilize or final rinse the film in a wetting solution that contains formaldehyde? Was the function of formaldehyde strictly as a biocide and is a biocide necessary when rewashing dirty, mold free film? Is there a universally effective or appropriate final rinse, when rewashing, for both Ektachrome and Kodachrome film?
  2. The formaldehyde was necessary to make the dyes stable, changing them chemically. Washing with water will revert that change. The formaldehyde is not just a biocide, it was necessary for image stability.
    All E-6 films (Ektachrome, etc.) require stabilization. The current E-6 process generates formaldehyde as a processing by-product, so it doesn't show explicitly in the formulas, but it happens.
    Until about 2000, Kodak C-41 (color negative) films required stabilization as well. Vericolor Print Film 5072 was the last one requiring stabilization.
    I don't have the Kodak Z-50 manual handy, but I think K-14 (Kodachrome) didn't require a stabilizer.
    Buying Flexicolor Stabilizer III is a handy way to get a final rinse with formaldehyde and Photo-Flo. Should work equally well for C-41 and E-6 films. Note that you also should use it when cross-processing E-6 film in a current non-stabilized C-41 line.
  3. Calumet Photo still has Flexicolor Stabilizer III.
  4. Last films that required the Supposed EPA nasty stuff was the VericolorIII films... All made by Kodak after that did not require it .... The E6 films did not need it a few years before that but could use it.
  5. There's something that's effectively formadlehyde in E-6 pre-bleach step. So while formaldehyde per-se isn't used, something similar is. Rewashing the E-6 film will undo that, so you need to restabilize, and the Flexicolor Stabilizer III is the easiest way.
    This has been described by both Ron Andrews and Rowland Mowrey, both former Kodak film engineers.

  6. The dyes used in most color films are in the form of an oily globule. The dyes are held in place entrapped in the gelatin binder of the emulsion. The structure of gelatin is such that it resembles, under the microscope, transparent spaghetti. The formaldehyde stabilizer forms a peptide bond, a cross linkage, that tacks the gelatin strands together at points were they touch each other. This locks the dyes in place preventing them from pooling.
  7. Thank you all! Just the information I was looking for!
  8. I can verify some of this, but not all.
    Certrain pyrazolone magenta couplers can react with the magenta dye that is formed from the combination of the coupler and oxidized color developer. This type of dye instability is called "pink toe fade" because it affects the magenta (pink) dye and occurs in the toe of the curve where there is plenty of unused magenta coupler. This reaction will occur in a few days to a few months depending on the temperature and humidity. It is a self limiting reaction. Once the unused magenta coupler has been consumed, the reaction stops. Since this only affects the lower part of the sensitometric curve (where there is plenty of unused coupler), it will affect the highlights of reversal films and the shadows of negative films.
    Most aldehydes in a neutral to alkaline solution will tie up the unused magenta coupler rendering it unreactive. This is what the stabilizer does (in addition to providing an ideal pH for dye stability). Some processes have aldehyde precursers such as gluteraldehyde-bis-bisulfite. These compounds release a steady stream of aldehydes into the solution.
    If the magenta coupler comes in contact with aldehydes before development, it will render the coupler unreactive. Formaldehyde fumes in wooden furniture cuased many green shadows in Kodacolor films. It was this problem that prompted the switch to aldehyde insensitive magenta couplers in color neg films. The toxicity of formaldehyde hastened the switch.
    One of the other problems that used to occur was in older processes like C-22 or E-4 that contained formaldehyde prehardeners. These solutions were acidic to avoid the reaction with the coupler. They also required a neutralizer to remove the aldehyde from the film before it got the the developer. If the neutralizer was not properly replenished or if the fumes from the prehardener were not properly vented, it would react with the coupler in the alkaline developer and result in green pictures.
    Does washing a previously stabilized film undo the action of the aldehyde? I don't know. I have no information one way or the other. It would be easy to find out if someone still has old film with aldehyde sensitive couplers. Two weeks in a wet oven (60 C, 70% rh) will induce the pink tow fade.
    There are other benefits of stabilizers. Getting the proper pH is one. There are probably others, but I'm not an expert on stabilizers.
  9. A tip-of-the-hat to Ron Andrews from Alan Marcus
  10. As I recall it most stabilizers had formaldehyde and zinc salts to stabilize the dyes. Also, formaldehyde hardened or toughened the gelatin. Be sure to use an appropriate formula because too much formaldehyde will leave bad white specs in the emulsion.
    If you spill formaldehyde just pour sodium sulfite on it, it will instantly change to an innocuous material with NO smell at all, then mop it up.

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