Color me purple – Some color developer formulas including C41 and RA4

Despite the modest resurgence of interest in film photography, supply issues remain a concern. This is nothing new; a few years ago, I already worried about this and figured that I wanted to expand my options when it came to in particular color chemistry for C41 negative development and RA4 printing. I started collecting formulas I found online, purchased the necessary chemistry and mixed quite a bit of (mostly) developers myself. Now seems a good time to share my findings with you. If anything, it might be convenient to have some key formulas in one place.

A little background

I admit that lately, I have mostly used Fuji minilab chemistry for my C41 processing. It’s pretty much bulletproof, cost-effective and you basically can’t go wrong with it. But how long will it remain available for consumers like me? And are there any other options that perhaps have the same or even better keeping qualities? Questions like these led me to mix my own color developers using dry components. I did this quite a bit for C41, and a bit less so for RA4. The results were just fine – I never did any very systematic comparisons with big-brand chemistry, but negatives and prints were by all means presentable and usable.

There was also a brief time I experimented with ECN-2 film, particularly Kodak Vision3 (also sold as CineStill without the remjet backing). Back when I did those experiments, there was no commercial offering of processing chemistry for consumers in convenient quantities. I think you could get 240 liter developer quantities, evidently not really intended for the average home user…so mixing one’s own chemistry was a sheer necessity. Getting the necessary components like the CD-3 and CD-4 color developing agents used to be somewhat challenging, especially in Europe, but it seems that lately, this situation has actually improved somewhat. But I digress…

Long story short, over the years, I collected some formulas from various (online) sources, mixed quite a bit of chemistry and collected all this information in neat little Excel sheets. Nice, but of no use to you. So I thought it might be useful for anyone interested to have a few useful formulas collected in one place. So let’s go!

I’ll focus mostly on the developers because those are the most critical processing step and generally the most challenging chemistry to get hold of. For bleaches and fixes, there are usually workarounds or black & white chemistry that can be repurposed. With the developers, there are less (or no) ways to get around the real thing.

I’ll cover C41, ECN-2 and RA4 developers in this post. Sorry, no E6 – I used to shoot a lot of slide film, but this is all >15 years ago and I had all of it developed commercially. Since then, I lost interest in color positives – they’re gorgeous, but I’m more of a printer than a photographer, and the only way to print E6 (at least with decent quality and without dedicating your entire life to it) is by scanning and inkjetting it. And I happen to not really like that approach.

Color negative / C41 developer

The current (and probably final) color negative process is C41 and it has been the standard color negative process for, ah, 30 years or so? There are, and have been, variants with different names form different manufacturers – for instance, Fuji sells CN-16 chemistry which is functionally the same as C41. It’s just their name for basically the same process.

It comes as no surprise then that there are several variants of the color developer formulae – and the same is true for bleaches and fixes, no doubt. Especially the bleach has gone through several generations of R&D, mostly improving speed, capacity and robustness. When it comes to developers, there are small (but probably significant) differences, while at the same time they all rely on the same backbone:

  • the CD-4 color developing agent,
  • potassium carbonate as an activator,
  • usually some buffering provisions (bicarbonate, bisulfite),
  • a little restrainer (usually sodium bromide and a really minimal amount of potassium iodide),
  • a small amount of sulfite apparently to suppress excess dye formation
  • an antioxidant to protect the CD-4 from oxidation; this is always hydroxylamine sulfate.
  • Usually there are some additional ingredients, like a wetting agent and a sequestering agent (calgon in old formulas or DTPA in more recent ones) to capture rogue iron ions that may spoil the broth.

For actual formulas, I found a couple of relevant sources (the list is not exhaustive). Firstly, there are the seminal posts by PhotoEngineer / Ron Mowrey on the Photrio forum. In particular this post where he presents what should be eerily close to an official Kodak C41 formula from the 1980s is of interest. Secondly, when I started out, I found the Bonavolta web page on C41 and RA4 chemistry very useful. Mostly because the author did a nice job at simplifying matters to the point where I felt I could actually do this. Then, there was the tedious but useful work done by user stefan4u also on Photrio, resulting in (among others) his ‘C-29’ version of the C41 developer. Finally, I once encountered some relevant patents by Kodak as well as Agfa that contained clues about C41 developer formulas. I collected this information in a table for comparison:

ChemicalPhotoEngineer / KodakBonavoltaStefan4U C-27Kodak patentAgfa patent
Potassium carbonate anhydrous34.3323437.4530
Potassium bicarbonate2.322.5
Sodium metabisulfite2.78
Sodium bicarbonate2.1
Sodium sulfite (anh.)0.383.52.84.03
Potassium sulfite3.0
Sodium bromide1.311.341.3
Potassium bromide1.51.5
Sodium iodide1.2 mg
Potassium iodide1.2 mg1.4 mg1.2 mg
Sodium chloride0.6
Hydroxylamine sulfate2.4121.81.972.5
Calgon (sodium hexametaphosphate)2
DTPA 40% solution8.43
DTPA3
A905 wetting agent 1 ml
CD-4 developing agent4.5254.54.394.5
Comparison of selected C41 developer formulas. All quantities in grams for one liter of working stock developer unless indicated otherwise.

The pH of the developer solution is generally 10.00, but there are small differences. For instance, The user-contributed C-29 formula is probably around 10.10 (going by its similar predecessor C-27 which would be 10.12), Kodak’s patent mentions 10.07 and the Agfa patent says 10.06. Photo Engineer mentioned a pH target of 10.0 +/- 0.05 for the formula in the column all the way to the left.

One note concerning the A905 wetting agent in the C-29 formula: it apparently was an ORWO product. I wouldn’t bother with it; if Kodak and Agfa didn’t bother with a wetting agent, I don’t think it’s particularly important to have one. Although I do have the distinct impression my Fuji minilab chemistry has a wetting agent in it given the way it makes nice bubbles.

At some point, I took in all this information and decided that it would be convenient to cut some corners here and there, mostly to work around difficult to get components. This resulted in this formula, which is similar to the Kodak formula provided by PhotoEngineer, but with some rounding and omissions. I’ve used it many times with good results, but have not done any color sensitometry on it – so no guarantees.

Potassium carbonate34.3
Sodium bicarbonate1.95
Sodium sulfite anhydrous0.38
Sodium metabisulfite2.78
Potassium bromide1.50
Hydroxylamine sulfate2.41
CD-4 color developing agent4.52
Target pH10.0 +/- 0.05
Simplified C-41 developer formula, quantities in grams, for 1 liter of working solution

This formula omits the iodide, which is apparently there for a perfect color balance and for acutance. I did experiment with developers with the iodide added and observed no visual differences with the film I tried. So it’s a ‘proceed at your own risk’ situation.

There is also no DTPA or other sequestering agent in this formula. This makes it more prone to any issues caused by metal ions, such as iron, calcium and magnesium. However, if the developer is used one shot, briefly after mixing and the water used is reasonably clean, I don’t think this needs to be a significant issue. I, for one, never noted any problems. The solution may be slightly cloudy due to calcium precipitates from the tap water, but I never noticed any ill effects from this.

Furthermore, the hydroxylamine sulfate (HAS) may be omitted if so desired. Since I was able to get some, I always add it, but if the developer is used shortly after mixing, the CD-4 doesn’t have enough time to oxidize and the developer should perform pretty much identical to the complete version with the HAS present. Keeping qualities will evidently be compromised – I don’t know by how much.

A note about pH and adjusting it: I find that when mixing a formula like this, the pH is usually not quite on target. It ends up around 9.90 or 10.10 or so – probably due to batch-to-batch differences of the CD-4 or other chemicals and of course measurement inaccuracies. Adjustment of pH is easy enough by preparing a 1% acetic acid solution and a 1% sodium hydroxide solution. Use a Pasteur pipette to add drops of either solution to adjust the pH. Stir the solution, wait for the pH to settle and repeat if necessary. Use sodium hydroxide solution to adjust pH upwards, and acetic acid solution to go downwards. If you feel you need to add too many drops of a 1% solution, prepare 2% or even 5% solutions instead. You’re the boss!

Watch out with the sodium hydroxide though; it will eat away the fatty acids in your skin. Ouch! The acetic acid is just vinegar – in fact, I always use cleaning vinegar. Apart from the acrid smell, it’s pretty harmless in this concentration. Alright, one more word of caution: several of the components in the formula above are toxic. The hydroxylamine sulfate isn’t something you’d want to put into yourself, your kids, your pets or even your backyard. The same goes for the CD-4, which is a nasty irritant to boot. So wear gloves, a mask and eye protection when weighing the dry powders.

Back when I was regularly mixing C41 developer, at some point I got kind of bored weighing out all those ingredients every time. So I figured it would be nice to make a concentrated stock solution instead and then dilute that for use. I was still using the Bonavolta formula then, so I used that as a starting point. There were a couple of problems, though.

Firstly, the CD-4 color developer isn’t stable in an aqueous solution. There is no feasible DIY solution for this to my knowledge, so I resorted to measuring that as a dry powder right before mixing the working stock. I’m aware of experiments of users on Photrio trying to make a liquid CD-4 solution, but I’m not convinced of the validity of this approach. My attempts to recreate the scant reports of success resulted in rapidly oxidized and unusable Cd-4 solutions. The good news is that the dry CD-4 powder, when stored dry and cool and in the dark, should be stable for many years or even decades.

Secondly, not all components play nice with each other in a concentrated solution. If memory serves, it’s particularly the sulfite and the hydroxylamine that shouldn’t be present in the same stock solution, so it’s inevitable to work with two concentrated stock solutions (and one dry powder, the CD-4 developing agent).

Here’s the solution I came up with, which seemed to work quite nicely, albeit that if I were to redesign it today, I’d use the Kodak/PhotoEngineer formula as a starting point. You could fairly easily adjust it along those lines.

C41 developer stock concentrate A: HAS

Hydroxylamine sulfate (HAS)200
Quantities in grams, for 1 liter of concentrate.

C41 developer stock concentrate B: Activator and restrainers

Potassium carbonate monohydrate257.1
Potassium hydroxide7.14
Potassium bromide10.71
Sodium sulfite25.00
Quantities in grams, for 1 liter of concentrate.

To make a working solution from these stocks and dry CD-4 powder, mix the following:

Water850 ml
Stock A10 ml
Stock B140 ml
CD-4 dry powder5 g

Adjust pH to 10.00 +/-0.05 with acetic acid or sodium hydroxide as described above. Because stocks A and B are used in a 1:14 ratio, I’d suggest mixing a much smaller quantity of A than of B so you don’t end up with a big jug of unused HAS solution.

ECN-2 film developer (and some auxiliaries)

I suppose there has always been some interest from the stills photography community in using ECN-2 stocks like Kodak Vision and Fuji Eterna (which is no more), but this really took off around the time when Cinestill started marketing rebranded Kodak Vision 3 rolls in 35mm and 120 format. I was curious about this development and bought some Vision 3 (with the remjet in place) from eBay and started testing. Later, I was gifted some Cinestill as well, so I ended up testing a couple of the Vision 3 stocks.

As mentioned earlier, no suitable developer was available to consumers at the time. Cinestill back then recommended developing their film in C41 chemistry, which I also tried to see how it would work out. It’s essentially a cross-process approach and my conclusion was that it was essentially a waste of potentially interesting film. So I decided to compound my own ECN-2 chemistry instead, which was helped greatly by the fact that Kodak had already released official ECN-2 chemistry formulas to the public. In the end, I still didn’t like the Vision 3 films much for my own work, because getting accurate color reproduction when printing the film onto RA4 paper in the darkroom appeared to be next to impossible. For scanning and digital processing, the results can be more than acceptable.

Let’s have a look at the ECN-2 developer according to the Kodak pdf linked to above:

Kodak anti-calcium No. 42.0 ml
Sodium sulfite (anh.)2.0
Sodium bromide (anh.)1.20
CD-3 color developing agent4.0
Sodium carbonate (anh.)25.6
Sodium bicarbonate (anh.)2.7
Kodak antifoggant AF-20005.0 ml
pH target at 25.0C10.25 +/- 0.05
ECN-2 developer formula as published by Kodak. Makes one liter, quantities in grams unless indicated otherwise.

A comparison with C41 chemistry shows a couple of key differences. Evidently, the actual developing agent is a different one, and this is crucial. Since the (oxidized) developer in a color system actually provides part of the dye molecule, the developer and the dyes embedded in the film are a closely linked and tuned pair. Hence, developing color film isn’t just a matter of throwing a developer at it and as long as it creates dyes, it’s all fine. For correct color rendition and chemical stability of the dyes, it’s crucial that the correct developing agent is used. The CD-3 developing agent is essentially a predecessor to CD-4, but still widely used as it’s not only present in ECN-2 developer, but also part of the E-6 color positive backbone as well as the correct developer for RA4 color paper.

Furthermore, the pH of ECN-2 developer is significantly higher, the salts used for the activator and inhibitor are all sodium salts (note that there is a mix of sodium and potassium salts in most C-41 formulas) and overall the developer is somewhat simpler than a C-41 formula. Whether the choice for sodium salts is simply a cost consideration, or results from a reduced need to make highly concentrated stocks, or if there are image-property considerations for this choice, I don’t know. I do know that it’s convenient, since the sodium salts are generally even easier to source, and cheaper to boot.

Still, there are some oddballs in this formula, namely the proprietary antifoggant and the chelating agent (anti-calcium). I believe that for home/amateur use, it’s valid to leave both out – the antifoggant will play a role in the shape of the toe of the film curve; it probably acts as a so-called ‘toe-cutter’ that removes the gradual rise of the curve at its start and makes this transition more instantaneous and linear. This will keep shadows a pure black and prevent crossover in the deepest shadows.

In a hobby environment, I would feel comfortably simply overexposing the film a bit and printing a bit darker to achieve pretty much the same thing. Overexposure was a necessity for RA4 printing in my experience anyway, because ECN-2 film developed ‘by the book’ creates a lower contrast gradient than C-41 has, and to match the film to the RA4 paper, this needs to be compensated for. In digital post processing, it’s of course even easier to deal with a slightly crossed over and lengthened toe of a film curve.

The anti-calcium could probably be replaced with a different chelating agent; perhaps sodium hexametaphosphate or DTPA as in C-41 formulas. However, i just chose to leave it out and accept that there may be a slight cloudiness to a developer when compounded using tap water, or just use demineralized water to prevent this.

All this yields the following simplified ECN-2 developer formula that I’ve used for some time with apparently good results (ignoring the poor match of ECN-2 film with RA4 paper). Note that I took the liberty to replace the sodium bromide with the potassium salt because the latter is a more common item in the drinks cabinet of a typical photographic darkroom.

Sodium sulfite2.0
Potassium bromide1.4
Sodium carbonate decahydrate*69
Sodium bicarbonate2.7
CD-3 color developing agent4.0
Simplified ECN-2 developer formula. Makes 1 liter of working strength solution; quantities in grams.

Note the (*) decahydrate species of sodium carbonate. I based the formula on this because it’s the common washing soda for sale in supermarkets around here, and that’s what I used at the time. If you use the monohydrate, which is also sold in some stores and is the default in photochemistry, use 30 grams instead of 69 grams.

Adjust pH to 10.25 +/- 0.05 just like in the official Kodak formula. The same approach as for C-41 developer can be used with acetic acid and sodium hydroxide solutions.

Just like with the C-41 formula, I at some point got bored of weighing all the components whenever making a batch of working stock developer, so I again devised a set of concentrates that can be mixed together with dry CD-3 powder (the same limitations apply here as with CD-4) to make a working strength developer.

ECN-2 developer concentrate stock A:

Sodium sulfite20
Potassium bromide14
Makes 1 liter, quantities in grams

ECN-2 developer concentrate stock B:

Sodium carbonate decahydrate344
Sodium bicarbonate13.5
Sodium hydroxide13.3
Makes 1 liter, quantities in grams

To make one liter of working strength developer, mix the following:

Water700 ml
Concentrate A100 ml
Concentrate B200 ml
CD-3 (dry powder)4.0 g
Makes 1 liter of working strength ECN-2 developer

Adjust pH to 10.25 +/-0.05 by adding drops of acetic acid or sodium hydroxide solution. I find that due to the inevitable inaccuracies in my haphazard work (sorry…) the pH was never quite on target, so pH adjustment was necessary with this formula. But having a pH meter when working with DIY color chemistry is a firm requirement anyway, so you already have (or at least ordered) yours at hand, right?

Note that solutions with sodium sulfite are prone to oxidation; the sulfite will react with oxygen in the water, and oxygen from the air will dissolve in water, so at some point the sulfite will all be gone. To prevent this, store concentrate A in entirely full, glass bottles with no air above the liquid. You could use an inert gas to purge any air from a bottle.

A note about the other ECN-2 baths, in particular the remjet removal pre-bath, the stop bath and the bleach. For the remjet removal bath, Kodak provides the following formula:

Borax (decahydrate)20.0
Sodium sulfate (anhydrous)100
Sodium hydroxide1.0
Remjet removal bath for ECN-2 film as published by Kodak. Makes 1 liter, quantities in grams.

Note the sodium sulfate and not sulfite! Since I don’t stock it (it should be easy to source, though), I always used an alternative that appears to work just as well: simply replace the sodium sulfate with, yes: sodium sulfite. Despite these chemicals being totally different, the concoction did do its job. Note that there are several remjet removal pre-bath formulas on the internet and they all seem to work to a greater or lesser extent. Also note that Kodak Vision 3 films pretty much always require some mechanical removal of the remjet remains after processing. In my case, a brief wipe with clean, moist fingers or a suitable cloth/tissue did the job just fine. If you look at Kodak’s suggestions for processing machine design, you’ll see that a mechanical scraper is indeed part of the remjet removal part, and this is indeed how it’s done in commercial facilities that process cine film stock.

For the stop bath, Kodak for some reason suggests a mineral acid bath, using sulfuric acid. While I believe that an acetic acid bath will in principle work well enough, I always just did this the Kodak way and got myself a bottle of battery acid (which is 37% sulfuric acid by default), which is generally cheap and easy to source, and used 10ml per liter of stop bath.

Kodak recommends a couple of bleach baths for ECN-2 stock. I conversed with PhotoEngineer / Ron Mowrey about these and frankly, I never got a straight answer why a C-41 bleach wouldn’t work. I tried it once or twice and observed no differences, so I suppose it’s alright to use a C-41 bleach instead of the Kodak ECN-2 options. However, in most of my film processing, I chose to again do it the Kodak way and picked the easiest bleach they suggested: a ferricyanide / bromide bleach. This is essentially the same kind of bleach that’s used for B&W work, e.g. for indirect toning or selective bleaching of prints. The formula I used is as follows; it is what Kodak considers the ‘alternative’ bleach:

Potassium ferricyanide40
Potassium bromide25
ECN-2 ‘alternative’ bleach along Kodak lines

This bleach works fine in my experience and has good longevity. I suppose it could even be replenished by adding some bromide once in a while. Sorry, I don’t know how much and how often, but it will probably not be very critical, as long as enough bromide is always present. Low bromide levels will reducing bleaching speed and ultimately result in incomplete bleaching. You can always re-bleach negatives that somehow don’t come out completely bleached.

Now, a note of warning is in place. I generally assume people to be sane and smart enough to stick to decent chemical safety practices, but here, I think it’s necessary to emphasize that a ferricyanide bleach when brought into contact with a mineral acid will form deadly cyanide gas.

This is important, because we’re skirting this risk by having a sulfuric acid stop bath and a ferricyanide bleach. Carry-over from the stop bath to the bleach might create serious problems, and for that reason, it’s imperative to wash the film and tank thoroughly between the stop bath and the bleach. This can be done by performing e.g. three water rinses of one minute each with constant agitation between the stop and bleach baths.

I can very well imagine that most people will choose to use a C-41 bleach instead of the ferricyanide bleach, since that practice will eliminate this serious risk from the process.

RA4 paper developer

This final bit covers RA4 developer for color paper. To be honest, I did this for a very brief while, but not a whole lot. The main reason being that commercially produced RA4 chemistry is still plentiful and easy to source, and quite economical. Other reasons include that a really good RA4 developer requires a couple of components that are very difficult or even impossible to source (at least economically) for the home user. Nevertheless, let’s give it a go. And yes, decent prints can be made with the less-than-ideal developer as well, so if for any reason you prefer to roll your own, it is a feasible option.

Unlike ECN-2 and like C41, RA4 formulas are still proprietary, but some have leaked to the public domain and/or have been reconstructed by the brave and tenacious among us. So let’s start with a formula comparison like we did with C41 based on what I have been able to find online with some quick searches.

The sources used are once again the late Photo Engineer / Ron Mowrey. Especially in this case a source to be taken very, very seriously because much of his work revolved around RA4 chemistry – in particularly the Blix part, but still, he was very intimately involved in the RA4 technology at Kodak, so let’s assume he did knew very well what he was talking about. He kindly shared his take on a chemistry kit for RA4 on Photrio. Also, once again, there is a simple approach offered by Bonavolta. There used to be a very good additional source by Steven Keirstead at Harvard, but sadly, that page has been taken offline. However! Thanks to the Wayback Machine, we still have a copy we can access. I also stumbled across a patent of Tetenal from 1996 which gives some interesting clues, but as always, patents are tricky sources to rely on, since they’re usually written to obfuscate instead of reveal crucial information. Still, I’ll include it for general interest.

Photo Engineer / Kodak @ PhotrioBonavoltaKeirsteadTetenal patent
Triethanolamine12.416 ml13 ml
Blankophor REU2.3
Tinopal SFP0.51.5
Lithium polystyrene sulfonate 30%0.30.92 ml
N,N-Diethylhydroxylamine (85%)5.47.03 ml
Etidronic acid 60%1.41 ml
DSEHA (disulfoethylhydroxylamine)9.5
Lithium sulfate2.71.35
Sodium sulfite, anh.5 (but see text below)0.068
Ethanol 95%2.48 ml
CD-3 color developing agent555.45
Potassium carbonate, anh.21.164023.727
Sodium bicarbonate2.36
Potassium hydroxide (for room temp. development – but see text below)(5)
Potassium chloride1.63.5
Sodium chloride0.51.27
Potassium bromide7 mg7.19 mg
Target pH10.03
+/- 0.05
10.3
Comparison of RA4 formulas as shared by various sources online. Makes 1 liter of working strength developer, quantities in grams unless otherwise indicated.

The differences are quite apparent – in particular, the Kodak / Ron Mowrey, Keirstead and Tetenal formulas seem to be part of the same family, while the Bonavolta formula seems to take a few liberties that may or may not be justified. Furthermore, the Tetenal formula seems relatively simple compared to the Kodak / Mowrey and Keirstead ones, but this may be due to the fact that the formula was published for patent purposes, and hence, the developer didn’t need to meet practical requirements such as good compatibility with a wide variety of papers or good shelf life.

This leaves the Kodak / Mowrey and Keirstead formulas as the ones to take seriously if top-notch quality is desired. Looking at these, I get the impression that Keirstead based his formula on information he obtained from Kodak or Fuji – the latter being unlikely due to the generally closed nature of Japanese companies when it comes to technical details. Interesting to note is that Keirstead published his formula as a triple concentrate with apparently decent shelf life and good ease of use. I compounded the information into a working strength single solution for the comparison above.

It’s also obvious from the various formulas that it will be challenging, or at least relatively expensive, to make an industrial quality RA4 developer at home. Many of the key components are difficult to obtain or very expensive, especially in small consumer-scale amounts. The Bonavolta formula is the exception, which is no surprise as it was apparently created with the specific aim to make DIY RA4 developer accessible for home users. I don’t expect it to have a particularly good shelf life and I do expect it to at least produce a significantly different color balance than a commercially bought developer. I can’t vouch for saturation being at the level the paper is capable of, or crossover to be entirely absent. It’s really a ‘use at your own risk’ formula. But at least it’s relatively simple to make.

I did actually make the Bonavolta formula and tried it – it works OK, BUT it requires some modification to the formula as taken from the Bonavolta web page. Firstly, don’t add the 5g/l potassium hydroxide. All it will do is boost the pH to an insane 12.25 or thereabouts. You might expect development to be pretty much instantaneous and excessive, but in reality, what seems to happen is that dye formation is actually hampered by the excessive pH.

Secondly, the sulfite content listed in the formula is much too high. It is apparently there to protect the CD-3 developing agent from oxidization, but sulfite in this application doesn’t work as it also inhibits dye formation. The result is very weak development, so incredibly low contrast and only a fairly weak magenta image on Fuji paper. Instead, mix up the formula without the sulfite and before adding the CD-3, add a tiny bit (perhaps 50mg or so; cf. the 68mg in the Keirstead formula!) and then mix in the CD-3. This will make a quite functional RA4 developer that is capable of producing neutral colors and decent saturation.

A note about the ethanol in the Keirstead formula. He mentions that it prevents bacterial growth in his concentrate, and that it makes the CD3 easier to dissolve. Indeed, when I made the Bonavolta formula, I found that the CD3 would only dissolve partially and some of it would float on top of the developer as small oil-like bubbles. Adding a squirt of generic bio-ethanol made these little magenta bubbles dissolve nearly instantly. Apparently the presence of a little ethanol helps; perhaps this is also part of the reason why some of the more arcane chemicals are present in the other formulas (e.g. the lithium salts), but there are likely additional reasons for this as well.

Because the Keirstead formulas are now a little hard / indirect to find, I’ll reproduce them here. He published them as open source, so I assume that it’s OK that they’re copied verbatim for posterity.

Keirstead RA4 developer concentrate part A

Triethanolamine240 ml
Lithium polystyrene sulfonate (30%)17 ml
N, N’-Diethylhydroxylamine, 85% Aqueous solution130 ml
Etidronic acid, 60% Aqueous solution26 ml
Makes 1 liter of concentrate

Keirstead RA4 developer concentrate part B

Lithium Sulfate50g
Sodium Sulfite2.5g
Ethanol 95%100 ml
Makes 1 liter of concentrate

Keirstead RA4 developer concentrate part B with CD3 added

Water40 ml
Part B as prepared above50 ml
CD-3 developing agent, dry powder10.00g
Makes approx. 100ml of concentrate

Mix part B with CD3 immediately before compounding the working stock solution, since the solution won’t keep well with the CD3 dissolved. It will oxidize, go deep purple and become unusable.

Keirstead RA4 developer concentrate part C

Sodium carbonate, anhydrous439g
Sodium bicarbonate43.6g
Sodium chloride (NOT iodized)23.5g
Potassium bromide 0.7% solution19 ml
Makes 2 liters of concentrate

Keirstead aims at a working strength developer volume of 1.85 liters. Perhaps he used a roller transport machine that took this amount of developer; it’s a bit of an odd amount, but you could scale up or down as you see fit. To make 1.85 liters of working strength developer, mix the following:

Water1000 ml
Part A100 ml
Part B with CD 3100 ml
Part C200 ml
Top up with water to make1850 ml
RA4 developer working strength mix ratio using Keirstead’s concentrates

Keirstead also provided a formula for an RA4-compatible Blix. Ron Mowrey / Photo Engineer also provided one through the Photrio link I gave earlier. Since that page is still easily accessible, I’ll leave it up to you to evaluate it if you’re interested, but I’ll duplicate the Keirstead formula here so it remains preserved easily accessible online:

RA4 blix according to Keirstead

Water1200 ml
Ammonium thiosulfate 60% solution240 ml
Sodium sulfite10 g
Sodium bisulfite10 g
Ferric ammonium EDTA, 52% solution175 ml
Glacial acetic acid (100%)12 ml
Adjust pH to 6.3 ~6.5 using ammonia (pH up) or acetic acid (down)
Top up with water to make1850 ml
Formula for 1850ml working strength RA4 blix

For now, this concludes this post on color developer chemistry. I say ‘for now’, because I may add content to this post as I see fit, but I feel that at this time, I’ve shared most of what I learned over the years and that I actually found useful in regular darkroom use. As you can see, I didn’t invent anything new. Yes, I mucked about a bit with concentrates based on simplified formulas – with all the risks for image quality associated with it. But I don’t consider that ‘new’, it’s just rehashing stuff that was already around and making it more practical for me to work with.

However, I still feel it’s valuable to have collected this information in one place. While I could relocate some things I had lost fairly easily, this was only possible because I knew what to look for and where to look for it, in general terms. I suppose that someone who just starts out looking for some good information on color developer formulas would have to spend a significant amount of time compiling this information. Hopefully I’ve been able to save you at least some of this time.

3 thoughts on “Color me purple – Some color developer formulas including C41 and RA4”

    1. Good question. We’d have to split this into two categories: generic chemistry, such as sulfite, carbonate etc., and photography-specific items such as the CD-3 and CD-4 developers. The first category is fairly easy and involves mostly ‘shopping around’. Much of these materials I generally find in supermarkets (carbonates, especially sodium, but also bicarbonate), online retailers of cleaning products (hydroxides etc.), wholesale food products suppliers or brewery supplies stores (e.g. sulfite, metabisulfite etc.) For the specialty items, it’s more challenging. Items like hydroxylamine sulfate delegates you to retailers of laboratory chemistry. Most countries have some of those; for instance, in The Netherlands there is labstuff.nl that also retails to private individuals (albeit with generally long lead times). I don’t know the situation for each individual country, so you’d have to root around a bit. Usually there are online forums where people discuss e.g. experimental chemistry and you can glean sources off of those. There are also photo-specific retailers spread across Europe. I don’t do business with them a lot because they tend to be a bit more pricy, especially on generic chemistry, but for some items (especially if you only need tiny amounts), they are a convenient source. And of course there is always eBay. Product offerings vary, but things like developing agents do pop up there from time to time. But I do admit that hunting down the various components of a developer can be daunting, at least in the beginning. Once you find a couple of good sources for various odds and ends, it gets easier. Be prepared to spend quite a few hours on google at first!

  1. Very interesting, thanks!
    I have been wanting to try the Bonavolta RA4 formula for a long time because it does not contain lithium (CAS 9016-91-5).

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