C41 film process: Are there over-bleach and the dangers of over-bleach?

[LomoSnap]

Often insufficient bleaching results in silver retention and leuco cyan dye problems. What if you bleach too much? What symptoms will he have? I have barely searched on the internet for the issue of over bleaching, does it really happen?
I use KODAK Flexicolor C-41 RA Bleach to process the film in Jobo. This is a very fast bleaching solution that only takes 1 minute to complete the bleaching process. Sometimes I forget to replenish it after use, so I worry about its effectiveness, I usually increase the bleaching time to 2-3 minutes after multiple uses, and it seems that there is no problem with the film developed.
So I am very curious, under what circumstances does excessive over-bleach, and how does it behave?

 

[Rudeofus]

One can think of two kinds of "overbleaching":

1. using a bleach, that's stronger than the process is rated for, e.g. C-41 bleach III for E-6 process, or ferricyanide bleach for E-6 or C-41. In this case you could actually lose archival stability, which is bad, but I have never heard about off colors or other image defects stemming from such use. Not recommended, but you will get usable results, which may or may not last for decades.
2. using a bleach, which is rated for this process, multiple times or for longer than the process expects: does not matter as far as I know. I could probably imagine problems popping up, if you bleach for multiple hours, but everything "reasonable" should be perfectly fine and should yield archivally stable results.

 

[lamerko]

As far as I know, ferricyanide bleach, for example, serves, in addition to its primary purpose, to release excess dyes from the film in some older processes. It would probably have some meaning along those lines. With the new processes it may not matter at all.

 

[koraks]

Sometimes I forget to replenish it after use, so I worry about its effectiveness, I usually increase the bleaching time to 2-3 minutes after multiple uses

That sounds OK to me. In fact, I do the same (with Fuji RA bleach), but I try to keep an eye on correct replenishment nevertheless.
No worries about 'overbleaching'; you're not doing any damage.

ferricyanide bleach, for example, serves, in addition to its primary purpose, to release excess dyes from the film in some older processes

I haven't been around long enough for that, I guess. I guess it's imaginable that very old dye couplers would be destroyed and perhaps broken down into partly water-soluble molecules by a ferricyanide bleach - but I admit I find it a bit of a stretch to believe this. The dye couplers used in color photography have been hydrophobic, 'oily' molecules for a very long time. I don't think there are very feasible ways to remove them from a gelatin emulsion without breaking the entire emulsion down.

The main concern with a ferricyanide bleach is as @Rudeofus mentions the risk of substantially reducing archival stability, which as I understand relies partly on radical-scavenging compounds that will likely be oxidized instantly by ferricyanide. From experience I know that contemporary C41 film and RA4 paper withstand ferricyanide bleach just fine - but what I don't know is how such a bleach affects the durability of the negatives or prints. I think there are valid reasons for concern, here.

 

[Rudeofus]

I haven't been around long enough for that, I guess. I guess it's imaginable that very old dye couplers would be destroyed and perhaps broken down into partly water-soluble molecules by a ferricyanide bleach - but I admit I find it a bit of a stretch to believe this.

Uncoupled dye couplers are handled by Formaldehyde, not by ferricyanide. What happened in the past: there were "4 electron dye couplers", which need 2 oxidized color developer molecules to form a visible dye molecule and have this leuco dye stage in between.

These leuco dyes were typically converted to real dyes by a sufficiently powerful bleach agent, and ferric EDTA was sometimes deemed too weak for that. If bleach was too weak, then a sizable fraction of dye couplers would not yield visible dye, which means reduced density and film speed. This was a bad situation and the reason of these many warnings "don't make your bleach too weak or you'll get leuco dyes".

As PE has stated on multiple occasions: all modern dye couplers are of the "2 electron" type (i.e. need only one oxidized color developer molecule to form a visible dye), and have been for decades. If you find a C-41 box in the attic, where portrait shots show cave men and dinosaurs, then you have to worry about leuco dyes. Every one else should just ignore this issue.

The dye couplers used in color photography have been hydrophobic, 'oily' molecules for a very long time. I don't think there are very feasible ways to remove them from a gelatin emulsion without breaking the entire emulsion down.

Those were "Fischer couplers", and the color developers for them contained Benzyl Alcohol to make these couplers accessible to oxidized color developer. Again a thing of the distant past, c.f. cave men & dinosaurs.

 

[koraks]

Thanks @Rudeofus for filling in the sizeable blanks in my reasoning!
When you say 'distant past', we're talking 1950s-1960s (and earlier) rather than 1980s-1990s, right? Just to give some perspective to the more subjective terms.

 

[lamerko]

Some processes like ORWO C-5168 were alive until the early 90's

 

[Rudeofus]

When you say 'distant past', we're talking 1950s-1960s (and earlier) rather than 1980s-1990s, right? Just to give some perspective to the more subjective terms.

I can't give you an exact year, but both the C-22 and the E-4 color developers contain Benzyl Alcohol, whereas their successors C-41 and E-6 do not. E-4 was introduced in 1966 according to Wikipedia, and C-41 appeared in 1972. Since C-41 uses masking and therefore gives much more leeway with choice of dye couplers (masking dye couplers are more complex, but you have more degrees of freedom with their spectrum), so it's quite likely, that color negative processes used modern couplers earlier than reversal processes.

Either way, "50-60 years ago" would be my best guess. No current material uses these couplers.

 

[czygeorge]

I remember in Z-131(or kodak specification book in Chinese,I can't remember accurately) it mentioned longer time bleach will not cause damage

At some early literature will mention the damage of over bleach because at that time the processing chem is not that perfect.Actually when use PDTA bleach in C-41and ECN-2 or EDTA in E-6,do longer bleach is very usual to avoid silver remaining

C-41 RA bleach is very stable to replenish-use in drum process if you do stoper to protect it from developer and adjust its PH

 

[Donald Qualls]

For both C-41 and E-6, all processes after color developer are intended to be carried to completion, so if you're using compatible chemistry, bleaching longer will do no harm at all. Bleaches intended for other processes (say, dichromate/sulfuric acid or permanganate/sulfuric acid B&W reversal bleach in place of rehalogenating bleaches for color processes) may have, um, bizarre results ranging from destruction of dyes to some level of solarization-equivalent results -- to black film.

Bleaching longer is one of the common ways to "stretch" kit chemistry (most of which uses blix, but the result is both bleaching and fixing longer when you want to remove all traces of developed silver and halide from the film), along with extended color development.