Correcting leuco-cyan dye in developed C41 film

I've been scanning many of my 4x5 C41 negatives. Though I have what I am

fairly confident are correct profiles for my scanner (an Epson 4990) and

for the films I've used for the past decade or so, I find that some not

insignificant fraction of my negatives have _very_ strange color casts

when scanned, which can be quite difficult to correct in postprocessing.

In fact, looking at the color histogram for these negatives in Photoshop

shows a huge hole in the cyan channel -- which makes me suspect that much

of the cyan dye in the film either originally developed as, or converted

later to (is this possible?) the colorless leuco-cyan form. I am not

tremendously surprised by this since I know about 50% of my film over the

years was developed with 2-part C41 kits, with combined bleach-fixes that

are notorious for leuco cyan problems (as I didn't know at the time).

If I can reprocess the film to give normal cyan dye, I want to. But some

people have advised me that it should be possible to repeat only the fix

step; thinking about the problem (that the cyan dye is in the wrong

oxidation state) I think it may actually be necessary to repeat the bleach

step as well. I have also seen recommendations to use a bleach for this

kind of reprocessing that differs from the standard C41 bleach.

Can anyone offer informed advice on this?

If the current problem is cyan leuco dye, it has probably been a problem since the film was processed. The oxygen in the air is enough to keep the dye in the correct oxidation state. It can even recover some of the cyan leuco dye that may have been present initially.

One change that might affect this is the recent conversion of some sheet film products from cellulose acetate buterate to polyester (Estar) support. With acetate (and I believe with acetate buterate base) the majority of the oxygen reaching the cyan layer comes through the base because dry gelatin is a good oxygen barrier.

If this is the problem, you can fix it by fully reprocessing or by skipping the developer and starting with the bleach. A well oxidized bleach will fix leuco dye problems. An old fix that has too much bleach carried into it can cause cyan leuco dye problems, but a fresh fix cannot fix it so you will need the bleach step.

<p >It is highly unlikely that the height of the water bath is the culprit. All of the fluids of the process are mainly water. Water retains heat, as it is a poor conductor, slow to heat, slow to surrender heat. As you agitate, by any method, the fluid movement insures uniformity of temperature. Stated differently, it is unlikely that there is any stratification of temperatures in the tank.</p>

<p >We look at the edge printing to detect insufficient agitation, particularly at a dot (.) character. The gelatin binder swells when wet allowing fluids to percolate about. In the high-density areas, the developer quickly exhausts. We need agitation to flush, circulate, and bring in fresh. Under low or no agitation conditions, spend developer wells out, being heavier, it exits and sinks. This spent developer flows downward and shields the film below from getting fresh developer. As it sinks, it induces fluid movement that brings in delayed fresh developer. We call this action bromide drag. We detect this by an area of lower density trailing a high-density area. The edge printing, particularly a period (.) will show a detectable tail like a comma (,). Over agitation seldom has a bad effect. </p>

<p >My guess, it’s the bleach or blix step. The C-41 film is susceptible to retained sliver and leuco cyan dye. The finished color negative wants all the metallic silver and silver salts gone. Initially the film is coated with silver salts. These are exposed in the camera. The developer is able to identify those salts that have been exposed and reduce them. The reduction is too metallic silver and a soluble salt. The salt dissolves into the waters of the developer the metallic silver remains imbedded in the gelatin. Unexposed silver salts are not affected. </p>

<p >Three incomplete dyes are present in the gelatin emulsion. All three are missing just one component. Color developer in the developer solution contains the missing dye component. The dye and the missing components combine only at sites that have metallic silver present. The dye blossoms, cyan in the red emulsion, magenta in the green emulsion, yellow in the blue emulsion.</p>

<p >These dyes in their incomplete state are leuco (Latin colorless). While all three blossom during the developing cycle, the cyan dye is tricky. The bleach or blix is EDTA, a chelating agent. Its job is to grab the metallic silver and prepare it to be dissolved by the fix. Additionally the EDTA requires oxygen to work. Also the pH of the bleach or blix must be on target. A lot can go wrong. </p>

<p >I think your film has leuco cyan. An incomplete blossoming of the cyan dye. Easy to find out. Just re-bleach and re-fix. If you are using a blix, just re-blix and compete the process as you would normally. My guess is, the re-process will fix the problem. </p>

<p >Why is bleach or blix bad? I need to know more. My guess in old - bad - or improper preparation or contamination. </p>

<p >Best of luck! </p>