Glycin-only developers "assumed to be one stop slower" -- Why?

[Raghu Kuvempunagar]

by the mid-90s Agfa and (on the basis of the TMax reversal kit MSDS) Kodak seem to have stepped away from KSCN or similar solvents in the FD in favour of specified molecular weight PEG and HQMS (or some sort of in situ synthesis in the 'commercial' MQ version - I think).

TMax reversal kit doesn't have Thiocyanate but it does have Thiosulphate as per MSDS.
Edit: TMax kit doesn't have Thiosulphate either but Formulary kit has it.

In my (admittedly limited) experience reversing a variety of films, I find one category of films easy to reverse without a silver halide solvent (e.g. HP5+, Kentemere 400) and other category needs substantial silver halide solvent (e.g. TMax 100, TMax 400). It just seems impossible, with developers available to me, to make reversal work well for the second category of films without a silver halide solvent. If anybody has got TMax films reversed by the 90's Agfa process that doesn't use halide solvent, I would like to know their experience. It's hard for me to believe that a silver halide solvent free reversal process will work for TMax films without somebody providing corroboratory data.

Interestingly, @dr5chrome has worked out a process that supposedly works well for both categories of films though his process pipeline has a mysterious FT stage which could be accounting for the differences.

 

[Lachlan Young]

@Raghu Kuvempunagar - that isn't the official Kodak Tmax direct positive kit. This is the correct MSDS, and it's p.44 you want. If you scroll further, you'll see that PEG is also used in the redeveloper.

 

[Raghu Kuvempunagar]

@Raghu Kuvempunagar - that isn't the official Kodak Tmax direct positive kit. This is the correct MSDS, and it's p.44 you want. If you scroll further, you'll see that PEG is also used in the redeveloper.

My bad. It's the Formulary TMax reversal kit that has Thiosulphate and not Kodak's. According to Formulary, they use a formula developed by Hans F. Dietrich. Not much I could find on his formula but this comment from the past is quite interesting:

If you are comfortable with compounding your own solutions, the Dietrich formula (D&CCT March/April 1988) works very well with TMX, but less successful with TMY. A couple of years ago we had a shootout between TMX/Dietrich and Scala and found that the former actually has a slight edge, and when we compared the prices it is also only a fraction of using Scala.

It's interesting that somebody who used both Dietrich's formula and Scala found that the Thiosulphate based formula gave better results than Scala.

 

[Rudeofus]

Other ortho litho films such as Kodalith did not give the same speed increasing behavior in these precision tests, but instead had some removal of highlight density and additional "smoothness" in how shadow density built up. Shadow density increased faster than control tests rather than maintaining that steep toe that litho film is known for. No additional shadow density (ie, didn't go from dmin to some density) was revealed though.

All this tells me is, that the actual black&white developer you used after the prebath is an inferior product. Whatever this prebath achieves, should and can be achieved by a well formulated black&white developer.

One of the interesting things about amines is that they are often used in color developers (even without a formula you can smell them!), but I've never seen an actual explanation for why.

I don't have TEA at home so I can't check, but is there a chance, that this "amine smell" could also come from an amine known to be in C-41 CD? Can you confirm, that this amine smell is also present in the alkaline concentrate part, i.e. the concentrate not containing the HAS and also not the CD-4?

I think that 3g/L of sulfite is not enough to efficiently regenerate metol and so the behavior of that is likely related to how ascorbic acid works, but with the additional effect on localized pH that ascorbic acid products would bring. I'm still studying and trying to search out notes for why it was formulated in this way and especially how it remains such a rapid developer despite being so dilute in terms of developing agents and carbonate levels. If anyone has any clues there, I'd definitely appreciate it. Film developing cookbook doesn't go into too much detail about it

Metol is not "regenerated" by sulfite, instead sulfite forms a sulfonate with oxidized Metol, and this Metol Sulfonate lets go of the silver halide grain that the oxidized Metol would have stuck to. If we assume, that less than 1g of Metol is used up during development of a roll of film, then 3 g Sulfite should be plenty. Little wonder, that FX 2 is very active with its rather high pH.

 

[Rudeofus]

Mention of HQMS-K (and BW reversal) brings up this rather interesting patent which suggests that by the mid-90s Agfa and (on the basis of the TMax reversal kit MSDS) Kodak seem to have stepped away from KSCN or similar solvents in the FD in favour of specified molecular weight PEG and HQMS (or some sort of in situ synthesis in the 'commercial' MQ version - I think).

The "new" developer proposed by Agfa in this patent still uses thiocyanate (called sodium rhodanide in the patent). The PEG of specific molecular weight is an additional developer accelerator, and together with the NaSCN the developer seems to reach the contrast the inventors were after. To my best knowledge current E6 FD products did not use PEG.

Mention of FX-2 has reminded me that some recent digging around in some papers about DQE (Detective Quantum Efficiency) and similar work on film information capacity from the late 70's brought up a number of citations to the effect that D-76 at 1+4 was apparently 'well known to be able to produce adjacency effects' - at least seemingly in the academic and research communities in a city in upstate NY on the shores of Lake Ontario. What this has now making me wonder is whether taking Haist's D-76 variant and modifying its stock solution to either the 20g/l Borax or 2g/l Metaborate of D-76K or DK-76 (respectively) might have useful effects when run at 1+4 - especially as in the contemporaneous late 30's literature that accompanied these variants, they were supposed to half or quarter (respectively) the development time of regular D-76 stock solution. On the other hand, DQE and similar work likely showed that the granularity/ speed/ sharpness relationship was more usefully exploitable/ expandable at the emulsion design stage than in any developer concoction.

DQE is very important if you fly spy planes over some place and want to extract the absolute last piece of information from these precious shots taken under high risk. However, as soon as you introduce adjacency effects of some kind, DQE actually goes down, and at the same time people like the image better. DQE is probably the best single parameter to rank development agents, but I would not use it to judge the final developer mixed with these development agents.

And yes, if you browse through scientific articles on photographic imaging from 50ies throughout the early 70ies, focus is clearly on emulsion making and theory of initial development, trailed at a far distance by articles about photographic processing. Note: the most significant advancement in development agents during the last 100 years was the switch from Metol to Phenidone, giving an improvement of about one half stop. Compare this with the improvements in emulsion making in that time frame!

Anyway, currently I'm looking for a tanning developer that doesn't need pyrogallol as a major ingrediant, oxalic acid as an oxidising agent (to get the tanning effect to work) or alternatively requires me to use dichromates for subsequent cross-linking effects to harden gelatin prior to hot water wash-off...

You do know about Alan Johnson's experiments with an HQ tanning developer, yes?

 

[Lachlan Young]

The "new" developer proposed by Agfa in this patent still uses thiocyanate (called sodium rhodanide in the patent). The PEG of specific molecular weight is an additional developer accelerator, and together with the NaSCN the developer seems to reach the contrast the inventors were after. To my best knowledge current E6 FD products did not use PEG.

That would explain the mystery chemical I didn't get round to checking up on - and more stupidly for me, I did note the seeming absence of KSCN from the disclosed E-6 FD in the patent. But it doesn't explain KSCN's absence from the 'commercially available' MQ first developer - which would seem to be the component used in Scala. Presumably in the MQ formulation disclosed, KSCN wasn't needed. Taking a guess, I suspect that the patent was an outcome of seeing whether E-6 FD could be minimally altered into a suitable component for the Scala process (to cut manufacturing costs & make it more adaptable to people running extant E-6 machinery?). I fully expect that the re-developer was a standard Agfa product too. It is certainly interesting that the KSCN containing developer (even with PEG and specific restrainer added) struggled to meet the specification of the non-PEG containing MQ developer which seems to have delivered thorough development without fogging issues. The small amount of Sodium Carbonate in the MQ FD has been puzzling me (everything else is potassium) - the only conclusion I can vaguely point at is that it reacts with the H2SO4 to form Sodium Sulfate (a de-facto in-situ pre-hardener?), though I am more than likely wrong about this.

DQE is very important if you fly spy planes over some place and want to extract the absolute last piece of information from these precious shots taken under high risk. However, as soon as you introduce adjacency effects of some kind, DQE actually goes down, and at the same time people like the image better. DQE is probably the best single parameter to rank development agents, but I would not use it to judge the final developer mixed with these development agents.

Yeah - aerial films value absolute resolution over sharpness, noise or latitude (nothing amuses me more than people losing it over nominal aerial film resolution numbers without bothering to look at the 50% MTF or RMSG or characteristic curve) & it's the opposite with films designed to be used at ground level - and then it all gets deep into the questions of 'image content' that Kriss etc wrote about. I have tracked down and briefly looked at the Mike Kriss chapter that Ron quoted the adjacency effect charts from - after library access is possible again, I'll need to go and take a closer look at it - it's not an afternoon's light reading.

You do know about Alan Johnson's experiments with an HQ tanning developer, yes?

Yes I have - though it's probably going to be challenging to find the Kodak articles Ron mentions - unless you've encountered any over the years? The formulae I've got here for the tanning developer is essentially Metol, Pyrogallol, Oxalic acid, BZT and a carbonate activator. HQ and carbonate does seem a reasonable research direction, probably together with something that will cause faster oxidation to get stronger tanning.

I have found a journal article from a Technicolor researcher in the 1960's that looks at various developing agents and oxidisers for tanning effect - I'll need to see if I can track down an accessible copy.

 

[Raghu Kuvempunagar]

That would explain the mystery chemical I didn't get round to checking up on - and more stupidly for me, I did note the seeming absence of KSCN from the disclosed E-6 FD in the patent. But it doesn't explain KSCN's absence from the 'commercially available' MQ first developer - which would seem to be the component used in Scala. Presumably in the MQ formulation disclosed, KSCN wasn't needed.

The commercially available MQ first developer described in the Agfa-Gaevart patent doesn't have Thiocyanate as you said. However, the experimental results presented in the patent are for just one film: "a commercially available black-and-white reversal film, e.g. that of film speed 200 Supplied by Agfa-Gevaert AG, was exposed using a grey Step wedge and was processed."

Having not used this Agfa-Gaevart film, I don't know which of the two categories of films it falls into. Whenever Scala 200 is discussed on internet, people say it was a film specifically engineered for reversal without giving additional details about the film. I still would like to know experience of those who have got TMax films processed in the "commercially available MQ first developer" described in the Agfa-Gaevart patent. I find it hard to believe that a development accelerator can make halide solvent unnecessary for TMax films but would be happy to proven wrong. Unfortunately PEG 400/1500 isn't available to me to try this developer on TMax films myself.

 

[138S]

Unfortunately PEG 400/1500 isn't available to me to try this developer on TMax films myself.

Searching ebay or alibaba "polyethylene glycol" there are many results, quite cheap

I find it hard to believe that a development accelerator can make halide solvent unnecessary for TMax films but would be happy to proven wrong.

My guess is that the right accelerator may contribute to need less the solvent. At the end any solvent action will decrease DMax potential.

The accelerator is very responsible for the infectious development, this is developing those non exposed crystals that are close to exposed crystals, the more the infectious development do that the lower DMin, so less solvent action required.

In my opinion we the home reversal practitioners do not know all the tricks that proprietary Pro labs may use, those densities stated by DR5 (for example) play in another division. I guess home reversal may be improved a lot.

Also I don't think PEG alone is the magic bullet, but perhaps it would be interesting to see what effect it has.

 

[Raghu Kuvempunagar]

Searching ebay or alibaba "polyethylene glycol" there are many results, quite cheap
.

I avoid buying chemicals from foreign countries as it can at times be a problem with customs for a non business user like me. Will try to see if a local chemicals dealer can get it for me.

The accelerator is very responsible for the infectious development, this is developing those non exposed crystals that are close to exposed crystals, the more the infectious development do that the lower DMin, so less solvent action required.

If PEG could cause infectious development, wouldn't it have found more extensive use in film photography, for example, as a component of lith developer? Or as an embedded additive on emulsions? Do you know of any application of PEG beyond Agfa-Gavert's reversal first developer? It seems implausible that Kodak and other companies didn't know about it in as late as mid nineties. Contrary to what is hypothesized, it's possible that PEG was used by Agfa-Gavert to reduce the development time a little and reduce oxidation of the developer in usage.

I don't know if you have reversed TMax films. To me it seems implausible that they can be reversed well without a halide solvent. I would love to know the experience of people who have reversed TMax films without a halide solvent.

 

[138S]

I don't know if you have reversed TMax films. To me it seems implausible that they can be reversed well without a halide solvent. I would love to know the experience of people who have reversed TMax films without a halide solvent.

I reversed TMax with the Foma reversal kit in the past... and I made several low solvent tests with it.

Problem with TMax is that you have also a second emulsion layer under the main layer and that second layer (cubic, small crystals, ortho) is of extreme low speed to ensure linearity in the extreme highlights. It will be extremly difficult you develop that silver halide in the first development...

So if you don't use a silver solvent those small crystals are to produce a fog in the second developmen that is to decrease DMin.

Now I'm trying a new approach I'm "inventing" I made several tests that are promising, but still it requires refinement, still you may try that:

1) Use a controlled light fogging, not a fogging developer.

2) Do the light fogging just before bleaching: L.F.B.B. ("light fogging before bleaching")

Why ???? let me tell the reasoning. You fog before bleaching, so in the highlights the metallic silver present shields the remaing halide crystals so they are way less exposed than those in the shadows, so a controlled second developer (not to total completion) will develop more the low ISO halide in the shadows (increasing DMax) and less the low ISO halide in the highlights, lowering DMin, that non (second) developed halide in the highlights will be removed by the fixer in the last bath.

This requires throwing the right Lux·second in a well controlled LFBB. And it may also require making calibrations for a refined optimization.

 

[Lachlan Young]

@Raghu Kuvempunagar - ADOX have pretty explicitly said that Scala (and new Scala/ Silvermax) are essentially Agfapan 100 (the real stuff, not rebadged Kentmere) with additional silver added (for better DMax) and a few minor alterations to improve reversal performance overall - mainly to do with the practical differences involved in using clear base stock, as opposed to the dyed base stock normally used for 135 BW film. There are various reasons why the effective speed goes up in reversal processing - Ron Mowery commented on that on several occasions I recall. Most emulsions could be readily altered to improve reversal performance if needed.

Regarding PEG and other things like PVP and PVA, they're more often used in the emulsions as additives where they can help the gelatin swell more effectively, enabling fuller development of the silver and hence higher density (see Mowrey, Photographic Emulsion Making, pg. 66).

Tmax 400 runs fine (as do both Delta 100 and 400) in the Agfa Scala process that Photostudio 13 have kept running (they got access to the formulae etc). They even allow 1-stop pushing of Tmax 400. Their only real restriction is that they prefer 120 and sheet versions of these films as they are coated on a clear base (for a good Dmin).

 

[john_s]

........ ADOX have pretty explicitly said that Scala (and new Scala/ Silvermax) are essentially Agfapan 100 (the real stuff, not rebadged Kentmere) with additional silver added (for better DMax) and a few minor alterations to improve reversal performance overall - mainly to do with the practical differences involved in using clear base stock, as opposed to the dyed base stock normally used for 135 BW film. There are various reasons why the effective speed goes up in reversal processing - Ron Mowery commented on that on several occasions I recall. Most emulsions could be readily altered to improve reversal performance if needed.........

Maybe not important: Identifying Scala: I noticed in some Agfa documentation about films' characteristics that the Spectral Sensitivity graphs of APX100 and Scala were absolutely identical and different to APX400. Reminded me of a pair of identical fingerprints. Document F-PF-E4 of 2003.

 

[Raghu Kuvempunagar]

1) Use a controlled light fogging, not a fogging developer.

2) Do the light fogging just before bleaching: L.F.B.B. ("light fogging before bleaching")

That's a smart idea and I hope it works well for you. It's similar to the controlled light based second exposure that @Ian Grant has mentioned several times in the past.

 

[Lachlan Young]

Problem with TMax is ... that second layer... ortho

First class (ideally Kodak connected and named) citation needed for this.

Otherwise you're just badly misreading the spectral sensitivity chart (which actually has lower blue and red sensitivity - relative to green - compared to the first version of Tmax 400). You'd also see a strange tonal break at the transition point between the emulsions if they were sufficiently differently sensitised as you claim. And the slow emulsion layer crystals aren't 'cubic', they're '3D' - there are lots of different shapes that non tabular crystals can be grown to.

Use a controlled light fogging, not a fogging developer.

The reality is that a lab running Agfa Scala's process is able to get good results out of TMY-II - so it can be done, it just means realising that old techniques for cinema negative film reversal altered for environmental concerns (it is important to note that Kodak apparently researched T-grain cinema BW films, but under the specific conditions of cinema film use they did not perform better than the extant 3D grain products) may not extend to 1980's and later Agfa or Kodak emulsions built using aspect oriented grain structures/ multilayer construction and/ or epitaxial growth techniques amongst others. What I suspect you are running up against is that under 'traditional' reversal processes, the newer grain structures are developing at different rates internally, rather than uniformly (unless a lower EI is used at the time of initial exposure) - and that is where HQMS-K, development accelerators, grain solvents etc come into play. There is more in common with the problems of colour film processing (ie getting multiple emulsions to develop with perfect simultaneity) than with assumptions based on k-grain emulsions of the deep past.

 

[138S]

and it required a level of extreme precision

Quite easy, the same than when making calibrations.

It's similar to the controlled light based second exposure that @Ian Grant has mentioned several times in the past.

Not the same by far, I make the re-exposure before bleaching, this is huge comceptual difference: using the metallic silver to selectively mask the re-exposure in the highlights.

 

[Lachlan Young]

Quite easy, the same than when making calibrations.

Ask yourself this: why did none of the manufacturers who had access to technical resources and process controls far in advance of any you have access to not recommend partial re-exposure in the post-WW2 era? It's likely because the chances of errors producing unusable results are very very high. Therefore processes that run to completion are better - and if you have a first developer that actually does its job, every other step only needs to run to completion.

 

[138S]

Therefore processes that run to completion are better - and if you have a first developer that actually does its job, every other step only needs to run to completion.

YMMV.

Developing to completion the halide remaing after 1st development will deliver a lot of fog for sure, any regular strategy you may be able to point to remove that fog (starting by solvent in 1st D) is to decrease DMax potential.

I want a brilliant DMax like that stated for DR5, so I'm looking for alternatives. L.F.B.B. "light fogging before bleaching" works in the good direction, when I finish the development of this technique I'll be able to tell you how good it is or not, for the moment I can only tell you that's promising. For the moment I'm extending DMax - DMin difference by 0.6D but it looks to me that I'll be able to reach way more.

First class (ideally Kodak connected and named) citation needed for this.

Making Kodak Film (R.L. Shanebrook) Page 18, Fig 16, Kodak T-Max 400 film, cross section, undeveloped.

Here is also mentioned: https://www.rangefinderforum.com/forums/showpost.php?p=1960818&postcount=4

 

[Raghu Kuvempunagar]

Not the same by far, I make the re-exposure before bleaching, this is huge comceptual difference: using the metallic silver to selectively mask the re-exposure in the highlights.

You may be right though I can't recall whether @Ian Grant meant light exposure before or after bleaching when he mentioned controlled exposure in the context of reversal processing. It's definitely smart IMO and if it works well then great. It's like contact printing the negative silver image on the unexposed halide image. Sort of.

 

[Lachlan Young]

Making Kodak Film (R.L. Shanebrook) Page 18, Fig 16, Kodak T-Max 400 film, cross section, undeveloped.

Here is also mentioned: https://www.rangefinderforum.com/forums/showpost.php?p=1960818&postcount=4

Neither make any mention of ortho sensitisation do they?

 

[grainyvision]

All this tells me is, that the actual black&white developer you used after the prebath is an inferior product. Whatever this prebath achieves, should and can be achieved by a well formulated black&white developer.


I don't have TEA at home so I can't check, but is there a chance, that this "amine smell" could also come from an amine known to be in C-41 CD? Can you confirm, that this amine smell is also present in the alkaline concentrate part, i.e. the concentrate not containing the HAS and also not the CD-4?

Metol is not "regenerated" by sulfite, instead sulfite forms a sulfonate with oxidized Metol, and this Metol Sulfonate lets go of the silver halide grain that the oxidized Metol would have stuck to. If we assume, that less than 1g of Metol is used up during development of a roll of film, then 3 g Sulfite should be plenty. Little wonder, that FX 2 is very active with its rather high pH.

Maybe the developer could be formulated in some special way to bring out this speed increase.. but I've yet to figure out any method of doing that. Developers I've used with the pre-bath include Dektol 1+20, DD-X 1+3, D-76 1+1, and others. I'm not using some crazy weird developer for most of this, though the original test that I did the A-B test in was a special D-23 formulation (~1/4 strength, with less sulfite) designed for low contrast. The results are always night and day. With the prebath, I can typically get some shadow detail even at ISO 25, while without it, I'm lucky to get shadow detail at ISO 3.

TEA to me has minimal smell unless you're heating it and hold your nose over the beaker. DEA is where it gets fishy really quick. Also most homebrew and patent formulas for color developers I've seen include amines but often not triethanolamine. They tend to be DEA or MEA or an ethylamine derivative. All of these I'd assume to have a stronger odor.

Yea, I forgot about that aspect. Metol is just removed by sulfite rather than regenerated. 3g of sulfite is enough to remove it, but it's also a matter of time scale. I know from lith developer formulation that 2g of sulfite can still be fairly slow to actually remove oxidized developing agents, especially if the developer is rapid in action and produces a lot of oxidation productions. Also FX-2 is somewhat high pH due to using carbonate, but 2g of carbonate is an extremely weak buffer in relative terms.

Searching ebay or alibaba "polyethylene glycol" there are many results, quite cheap

My guess is that the right accelerator may contribute to need less the solvent. At the end any solvent action will decrease DMax potential.

The accelerator is very responsible for the infectious development, this is developing those non exposed crystals that are close to exposed crystals, the more the infectious development do that the lower DMin, so less solvent action required.

In my opinion we the home reversal practitioners do not know all the tricks that proprietary Pro labs may use, those densities stated by DR5 (for example) play in another division. I guess home reversal may be improved a lot.

Also I don't think PEG alone is the magic bullet, but perhaps it would be interesting to see what effect it has.

Unsure how related it is, but ethylene glycol is very often an MSDS listed ingredient in commercial lith developers (though I've never seen a homebrew formula containing it). I think it would be reasonable to assume they could contain polyethylenes as well if they are non-toxic enough to not need listed on the MSDS

I highly doubt that infectious development is a desirable property of any reversal developer, and if so it would require the developer to use a minimal amount of sulfite (often less than 2g per liter, but more can sometimes be used).

 

[138S]

Unsure how related it is, but ethylene glycol is very often an MSDS listed ingredient in commercial lith developers (though I've never seen a homebrew formula containing it). I think it would be reasonable to assume they could contain polyethylenes as well if they are non-toxic enough to not need listed on the MSDS

Ethylene glycol is highly toxic, it is used in cars mixed with water in the engine cooling circuit. Propylene glycol is not toxic and it can be found in food grade.

Polyethylenes (glycol) are polymers, a different animal with 500 to 8000 times higher molecular weight.

I highly doubt that infectious development is a desirable property of any reversal developer, and if so it would require the developer to use a minimal amount of sulfite (often less than 2g per liter, but more can sometimes be used).

For reversal, energic 1st developers are used, which promotes infectious development, I understand. The more infectious 1st development happens in the highlights the less silver solvent effect you need to clear those highlights, and if you play less solvent effect then more silver is available to get a higher DMax, in my view there is no doubt that 1st developer is desired energic to promote the resulting infectious development. Think that paper developer class is often recommended for reversal because it's energic.

 

[mshchem]

 

[138S]

Neither make any mention of ortho sensitisation do they?

True... Fig. 16 says that we have the low speed cubic layer under the tabular higher speed layer, sorry, I thought you were asking that. The ortho nature of the deep layer is seen in the T-Max datasheet, see the spectral sensitivity graph, in the curve labeled "1.0 greater than D-min" you see a great sensitivity drop from 600nm that is not seen in the "0.3 greater than D-min".

Anyway if you don't belive it then make a T-Max calibration with red light and you should see a graph shouldering way earlier than if making the calibration with blue light.

Also anyway ortho or not is irrelevant for the difficulty it has developing the T-Max deep layer in the 1st development, as the important factor is the ultra low speed it sports to conserve linearity in the extreme highlights, at that overexposure level you mostly have bright light sources or glares.

 

[Ian Grant]

You may be right though I can't recall whether @Ian Grant meant light exposure before or after bleaching when he mentioned controlled exposure in the context of reversal processing. It's definitely smart IMO and if it works well then great. It's like contact printing the negative silver image on the unexposed halide image. Sort of.

Reexposure is always after the bleaching, or it's done chemically in the 2nd developer, as it's often done while film is on a spiral you can't do it before bleaching or you'd have very poor uneven results. There's noprocess that used the image from the firts developer as a mask. Also bleaching after re-exposure will affect the 2nd latent image.

There were mecahnical processes that used exposure control for reversal and timed 3nd development was also used rather than development to completion. Early Ektachrome didn't use development to copletion for the 2nd developer nor did Agfa and Agfa based colour reversal. E6 was the only process where 2nd (colour ) development was to completion

Ian

 

[138S]

Reexposure is always after the bleaching, or it's done chemically in the 2nd developer, as it's often done while film is on a spiral you can't do it before bleaching or you'd have very poor uneven results. There's noprocess that used the image from the firts developer as a mask.

Ian

This is what presently I'm investigating, as a new way to do it. Using the metallic silver reduced in the first development to cast a proportional shadow in the re-exposure, so highlights will be cleaner with less solvent required, as halide in the highlights will be less exposed. And less solvent is higher DMax potential.

My next step is partially bleaching, then rinse, controlled light re-exposure, ending the bleaching. In that way we adjust how much shadow we cast in the highlights in the re-exposure.

Well, just a project...