Who’s afraid of cyan, yellow and magenta? Using color C41 and RA4 chemistry at home

I regularly speak to people who would like to start doing color development (film or prints) at home. Often, they’re shunned by the prospect of having to deal with color chemistry in a home darkroom setting. Please don’t let it stop you, though. Doing color work in a home darkroom is really pretty easy. And it doesn’t have to be very expensive, either.

In this blog, I’ll limit myself to processing C41 film and RA4 prints, since those are my main silver-gelatin color interests at this point. You can extend the contents of this blog for the most part to ECN2 and E6 development as well, but I will not go deeply into specific issues related with those processes or self-made chemistry. For color negative and prints, I have a collection of chemical formulas in a separate blog entry.

Also, it’s a long piece. Lots of text. This may elicit the thought that apparently, color processing is very complex. Well, it is if you get down into the details, but you don’t have to for the most part. The main messages of this blog are:

  1. If you consider doing color processing at home, just do it. Don’t let anyone or anything stop you. It’s great fun, very satisfying and it’s not very expensive.
  2. It’s basically a matter of following the instructions and using common sense.

If you don’t like reading, then I’d suggest to keep it at the above two remarks and go on your merry color-processing way! If you do like words, hang on. I’ve got plenty of them. But I’ll mostly just end up underlying the statements above.

Here’s a table of contents of this blog so you can scoot over to the bit of your interest if you don’t feel like reading the whole thing:

A very brief word on safety

Important announcement first: I’m not going to delve deeply into issues of safety, either human/personal safety or environmental responsibility. I assume that anyone who works with chemistry at home is capable of figuring out how to not get chemistry on or in their body, reading safety labels and disposing of their chemistry in a responsible way. This goes for color chemistry as well as black & white photo chemistry, but just as much for paint brush cleaner when painting, ceramic varnishes when doing pottery, drain cleaner and chlorine bleach when cleaning the house.

Moreover, in my view, color processing of C41, ECN2 film and RA4 prints is not dangerous if basic safety measures are observed. Don’t drink your developer or blix. Don’t put your ungloved hands into either and then, without washing them, go and have lunch or feed the baby. Don’t mix liquids together unless you understand what you’re doing, chemically speaking. Don’t put your chemistry in attractive soda bottles in a cupboard where Junior may be tempted to sample the attractive yellow ferricyanide bleach. Other than that, color chemistry doesn’t emit particularly obnoxious vapors or otherwise pose an unmanageable threat to whatever life forms may inhabit your dwelling.

So don’t let this stop you.

Challenge #1: Options to choose from

The first challenge people often bring up is that it’s supposedly difficult to get the right materials for color processing. Depending on where you live, this may or may not be the case. If you’re in the US or Europe, you’re in luck, as there will be options to choose from. On other continents, your choices may be more limited and in a worst case scenario may have to source materials from across the planet (esp. South America, Australia/New Zealand and Africa).

When selecting chemistry, the main choice you have is between a hobby kit intended for domestic use, or a small professional kit intended for a minilab setting.

The amateur kits are generally the easiest and the out of pocket spend is generally a bit lower. You get a reasonable quantity of chemistry to make between 1 to 5 liters of processing chemistry. Popular brands are Adox, Bellini, Fuji Hunt, Cinestill and Jobo. Quality is mostly alright to excellent.

Cinestill and some of the more obscure/smaller brands may cut corners here and there. For instance, Cinestill apparently sells a ferricyanide bleach with their Cs41 kit for color negative development, and while it works, it’s not a bleach that was ever qualified for C41 film processing and the effects it has on dye stability (i.e. will your negatives fade or discolor in long-term storage) are unknown.

Chemistry intended for minilabs is generally (much) cheaper on a per-liter basis, but since you buy a larger quantity at once, the out of pocket spend is generally higher. But if you accept that, you’re set for a long time of color fun in the darkroom with a single purchase. The brands to look out for are Fuji Hunt, Kodak (their color chemistry is expected to make a return shortly, after a few years of uncertainty at the mercy of SinoPromise) and Champion.

One challenge with minilab chemistry is that you have to deal with replenishers. This is because in a commercial setting, chemistry is used over and over again, and it’s being kept in good working order by replacing a little of each bath at a time (replenishment) in addition to some other conditioning techniques (especially bleaches, fixers and bleach-fixers).

Documentation for minilab chemistry therefore always includes mixing instructions for a ‘fresh tank’ solution as well as for a ‘replenisher’. Moreover, you’ll find that the concentrates that are sold are for this replenisher, as well as separate ‘starter’ solutions for most baths. This applies for instance to color developers (C41, RA4) and bleaches.

Empty bottles of a 10-liter Fuji Hunt Environeg minilab C41 developer replenisher kit.

The starter concentrate is used to make a freshly mixed solution behave like it is a ‘seasoned tank’ through which a quantity of film or paper has already passed. When you run film or paper through a color processing line, the pH (acidity or alkalinity) of the processing solutions will be affected and some chemicals will leave the film and dissolve into the processing chemistry (particularly halides; bromide, iodide, chloride). The starter solution performs the function of bringing a freshly mixed, never used solution up to the pH and concentration of halides (esp. developer starter) of a processing bath that’s in active use.

If you use minilab chemistry, you need the starter solutions as well for the developer (both C41 and RA4). For other baths (esp. bleach) you do not really need the starter. The replenisher itself is usable on its own.

For instance, if you’re going to start with Fuji Hunt chemistry, your shopping list may look something like this:

Fuji cat. no.NameQuantity
954743EnviroNeg Developer Replenisher LR AC2x10L
972497EnviroNeg Universal Developer Starter AC6x1L
971135EnviroNeg RA Bleach Replenisher VR AC2x5L
992024Negacolor Fixer & Replenisher RA4x10L
Fuji HUNT minilab chemistry for C41 development

There’s also a stabilizer, but in all honesty, you don’t really need it – neither for C41 film, nor for RA4 paper. There’s a lengthy thread about stabilizers for C41 film, but the short of it is that modern film (since the 1990s) doesn’t require a stabilizer. A wetting agent and maybe a biocide against fungus could be used, and products sold for B&W processing (Photoflo, Adoflo etc.) will function as the former.

For color RA4 prints, the shopping list could be like this:

Fuji cat. no.NameQuantity
970632CPRA Developer Replenisher AC4x10L
979328EnviroPrint Universal Developer Starter6x1L
995936CPRA Digital Pro Bleach-Fix & Replenisher2x10L
Fuji HUNT minilab chemistry for RA4 development

Concerning the quantities in the tables above: in each box there are often multiple ‘kits’ that can be used stand-alone. For instance, the C41 developer replenisher is listed as “2x10L”, which in fact means that the box contains two separate kits, each one being good for 10 liters of developer replenisher (it’s actually more – see further on under ‘Mixing’).

Some resellers may be so kind as to split out individual boxes and sell you part of a kit if an entire pack is too much. For instance, the box size of 6 bottles of developer starter will last a home user many years, so a reseller may sell you just one or two bottles and sell the rest to other customers. If you’re in Europe, I have good experiences with this shop in this sense: https://fotofilmfabriek.nl/ Just contact the owner and tell him what you need. He’s always been very helpful to me, also in parting out RA4 paper rolls that come two in a box for the smaller rolls (e.g. 12″/30cm).

Challenge #2: Mixing it right

If you can mix B&W chemistry, you can mix color chemistry. It’s the same thing, really: just follow the manufacturer’s instructions. Especially the home kits will have instructions that are clear for amateur users. More importantly: you’ll find the instructions in the box.

Minilab chemistry is slightly more complex because there are many more options and good documentation may not always be easy to find. I’ve bought quite a bit of minilab chemistry and it virtually never comes with any notable instructions of any kind. Fortunately, Google is also my friend…

For instance, for the Fuji chemistry I listed out above, the documentation for the C41 negative processing is under this link, while you can find the RA4 documentation by clicking here. If either one fails, just google for “EnviroNeg technical bulletin” for the C41 stuff and “EnviroPrint technical bulletin” for RA4. Fuji’s website management isn’t all too stellar when it comes to finding this stuff, but fortunately, Google does a great job indexing it anyway.

The minilab chemistry tends to give several mixing options for each bath. For instance, here’s the table for the C41 EnviroNeg LR AC developer:

The first line is for mixing the developer replenisher. This is intended for e.g. processing machines that have a tank for replenisher and that add the replenisher automatically do the developer in the correct amounts for the film processed. I do not recommend running a C41 replenished system in a home lab setting since the volume is virtually always too low to keep things stable.

The ‘TANK’ mix is what you’re actually looking for in a home setting, and they’re giving two ways to mix it: one is directly from the concentrates, and one from the replenisher that has been mixed in accordance with the first row in the table. I always just mix the C41 developer directly from the concentrates, so I ignore first and the last rows and go for the middle option.

Note that the 10 liter kit of the developer replenisher will actually yield 12.5 liters of developer with starter and additional water added to it

For RA4, I do personally run a replenished system, so I mix the replenisher for that developer instead, unless I’m starting over with a fresh batch of developer, in which case I’ll mix a ‘TANK’ solution in accordance with the RA4 mixing table:

For the bleach, fix and bleach-fix, just use the instructions for mixing the ‘replenisher’ and forget about any starters, regardless if you’ll actually use them in a replenishment system or for single use (‘one shot’).

Challenge #3: Using it right

When people talk about color processing, I often hear things about temperature control being very critical etc. I’m OK with people saying that as long as they’re basing themselves on actual hands-on experience. It saddens me if people say it because they believe color processing is very complicated and it’s necessary to ‘warn’ others about it. It’s really as difficult or easy as you want to make it on yourself.

So there are roughly two ways of doing this: the first is doing it by the book in as many respects as possible. This will ensure you’ll get optimum results all the time, every time. You’ll also spend a lot of time translating instructions that are really intended for large labs with high processing volumes into a domestic situation where you may run maybe a few rolls a week and a couple of square meters of paper, if that. You’ll also find yourself shopping for a densitometer, color negative test strips (doable) and RA4 paper test strips (they exist, as I’ve seen them, but try purchasing them as a hobby user!)

The second way is to allow yourself a little leeway and take some liberties here and there. This may result in negatives or prints that deviate from the norm a little (or maybe a lot), but as long as you don’t overdo it, it won’t be noticeable unless you’re going to do systematic analysis and comparisons (which would quickly get you back into box one).

I’d suggest a workable compromise that sits somewhere in-between these extremes. It may not get you to the level of what wedding photographers in the 1990s required when they would shoot the same film stock every day and would want all prints to come out identically color balanced with the exact same settings regardless of which session, season etc. the negatives were shot and processed or the prints were made. But the approach below will get you perfectly printable negatives and excellent prints for amateur use.

For color negative (C41) processing, I’d strongly suggest using the developer just once and then discarding it, and using a rotary development system (e.g. Jobo CPE/CPA, or a roller base and a regular tank) to minimize the amount of developer used. Alternatively, use your developer in a only a few sessions immediately after one another (a day or two in-between is OK, but see further on about storing your chemistry) if you don’t have access to a rotary setup and have to rely on manual inversion (e.g. Paterson tank in a tempering bath).

Theoretically it’s possible to replenish your developer, but it’ll be challenging to get really stable results this way if you only process a couple of rolls a week. And practically, it’s certainly possible to try and stretch your developer by reusing it until the negatives start looking funny to the naked eye, but experience tells me (and warns you) that by that point, you’ll have a decent stack of incorrectly processed negatives that are impossible to really salvage. Photoshop magic may still rescue the images, which could trick you into believing all is well, even if it isn’t.

Using the developer (almost) one shot, however, guarantees consistent results and leaves you with nothing to worry about. Minilab chemistry in particular is pretty affordable on a per-liter basis, so costs are not much of an issue. In a Jobo 1510 on rotary, processing a single 36 exp. roll would cost me less than €0.50 in developer if I use the developer one shot, or half that if I run a second roll right after the first one in the same 150ml volume. The fixer is also fairly cheap and I personally use it one shot, always.

The bleach is a different story. Its capacity is hue and it stores really well (see below), so feel free to reuse it – but replenish it appropriately. Replenishment rates are around 7.5ml of the replenisher concentrate for Fuji EnviroNeg RA bleach, which works out as 10ml of working strength per roll. I keep around a 500ml bottle of working strength bleach from which I take whatever I need for a developing session. After processing, I add the required amount of replenisher to the bottle, and then top it off with the used bleach. The very little excess I discard.

For RA4 prints, I use the developer in a replenished system, which in my experience works just fine. Even over a longer period of time (many months or even several years) and with infrequent use (once every few weeks) the chemistry tends to survive when maintained properly. Replenishment is the key; I replenish the developer and the blix according to the chemistry manufacturer’s recommendations, usually at the start or the end of a session.

Replenishment rates for paper chemistry are usually provided in volume per surface area and is specific for the chemistry you use. For instance, here’s a little table for recent Fuji Hunt RA4 developers:

Note how the rates are given in milliliters per square meter (ml/m2). At the end of a session, I sit down with the calculator and determine how much developer replenisher I need to add. I often print at a size of 20x30cm, so I simply key in 0.2 x 0.3 x [number of sheets processed] x [replenishment rate].

For instance, I’m currently at the tail end of my Fuji Hunt MP90 developer, which calls for 90ml/m2 according to the table above. So after a session of e.g. 30 prints, I’d have to add 0.2 * 0.3 * 30 * 90 = 162ml of developer replenisher, which I would generally round up to 200ml. The MP90 developer is a convenient monopart concentrate that’s mixed one part to four parts of water, so I measure out 40ml of replenisher concentrate, add 160ml of water and add that to my developer storage tank. I then top up with the developer I’ve just used during the session, and discard whatever won’t fit into the storage tank.

When switching to CPRA developer, I’ll stick to the higher end of the replenishment table because a low-volume setting generally is harder on the developer than the typical lab setting the chemistry is optimized for.

I end up discarding very little chemistry, because there’s always some chemistry that carries over with the prints to subsequent baths or the wash tray. Replenishment not only keeps the processing chemistry alive, it also deals with inevitable attrition.

For completeness’ sake, these are the replenishment rates of current/recent Fuji Hunt RA4 blixes:

Challenge #4: Getting the temperature right

In terms of temperature control: yes, temperature matters, but there’s no need to be extremely fussy about it in my experience. Whether you use the tempered water bath in a Jobo color processor (or any of its modern alternatives) or a sous vide stick (CineStill’s darkroom version, or any low-budget culinary version that really works just as well) – temperature accuracy and consistency will really be good enough for mere mortals such as you and I.

Heck, even ‘fly by’ temperature control will work, where you heat up your processing chemistry to a temperature above the desired set point before starting development, and just accepting that the temperature will drop during development with the tank just sitting on the counter (agitated frequently, of course) or roller base. If you do some measurements with your tank and a typical volume of processing liquids, you can determine that if you start for instance at 39.5C, by the end of a 3m15s development time the contents of your tank may have dropped to 36.5C, so the average would be nicely around 38C where it needs to be for C41 processing. No sweat!

Temperature control is also only (sort of) critical for C41 developer. The other steps are uncritical and anything above 30C or so in practice will be fine. You can even do the bleach and fix at room temperature if you extend the time for these steps. By how long? Well, long enough – let’s say 10 minutes for each, which will be plenty. There’s no ‘too long’, practically speaking, since both bleach and development ‘go to completion’. This means the chemistry just keeps working until there’s nothing left to do (convert image silver into silver fixable halide resp. fixing out silver halides), after which point it just sloshes around harmlessly in the tank.

For RA4 printing, the easiest approach is to use a roller transport processor, but these are fairly scarce and tend to be expensive when in good condition. The alternative is to process prints one by one in drums on a roller base. Heat up the chemistry in a tempering bath with e.g. a sous vide cooker. Then measure out the amount of developer, stop bath (optional; see below) and blix for your print or test strip. From this point, there are two options: (1) pour back the developer and blix to the main bottles in your tempering bath, and replenish them. Or (2) run a one-shot system where you discard the developer and perhaps also the used blix. My preference is very firmly with (1) because I find option (2) too wasteful when it comes to processing paper, and really unnecessary.

Personally, I’ve never had the hots for doing RA4 prints in drums, although I tried it. The thing is, after each strip or sheet you need to carefully dry the inside of the drum so that no water droplets can drip down the next print before the developer goes in. Uneven wetting of the paper with water before it’s being developed will show up as very apparent density differences especially in mid-scale tones. I found I spent too much time to my liking drying drums, so before I got my roller transport processor, I used trays.

RA4 print development in trays. One tray of developer, then stop bath, blix and a wash tray.

Fortunately, RA4 paper can be processed just fine at room temperature. Try a development time of 1m30s or 2m00s. When starting out, develop a test strip of fully exposed (to normal room light) paper – develop, blix and wash as normal. Then dry it and verify it is really pitch black without a hint of blue. If the black is a little blue, try another strip but develop for 30 seconds longer. Choose the first development time that makes the fully exposed paper reach a solid and convincing, pure black.

Challenge #5: Filling in the gaps

Better late then never – let’s have a look at a typical C41 film processing sequence:

  1. Optional pre-wash
  2. Development
  3. Optional stop bath
  4. Optional rinse
  5. Bleach
  6. Optional rinse
  7. Fix
  8. Wash
  9. Optional stabilizer, conditioner or final rinse

If you process ECN2 film, you’ll have to thrown in a ‘remjet removal’ step somewhere in there. I’m not going to go deeply into it here, because I already did a blog on it recently.

Also, amateur-oriented kits for C41 processing often use a blix (bleach-fix) instead of separate bleach and fixer. I prefer the latter, but a blix also works OK and is of course a simpler process with one or two fewer steps.

And a similar process flow for RA4 paper:

  1. Development
  2. Optional stop bath
  3. Bleach-fix
  4. Wash
  5. Optional stabilizer or conditioner

Note that in both process flows above, there are a couple of ‘optionals’. They require some explanation, I think, as some of them make sense, some are in my view totally superfluous, and for some it depends a bit on how you look at things.

To pre-wash, or not?

Pre-wash for film is a contentious topic. Some swear by it, others swear at it. It’s basically just a water wash of a few minutes at the development temperature. The logic is that this will allow the film, reel and tank to quickly reach processing temperature so that the subsquent developer doesn’t cool down, causing underdevelopment. Also, wetting the film thoroughly can (the proponents say) help prevent unevenness in development (‘flow marks’ or ‘surge marks’).

In my experience, a pre-wash is useful for me, personally, with my equipment and working methods, when color developing 120 roll film and 4×5″ sheet film in Jobo 1500 series tanks. I find it unnecessary for 35mm film in the same series tanks. With especially 4×5″ sheet film and to a lesser extent 120 roll film, I tend to have small, wave-like density variations along the edges of some rolls or sheets. This issue does not pop up if I use a pre-wash, so that’s what I do. Interestingly, others have told me that their experience is the exact opposite: they get surge marks if they do a pre-wash, and perfect negatives if they immediatelty pour in the developer.

My advice is to start without a pre-wash, and to add one if you have any uneven development problems that may be fixed by adding a pre-wash.

Pre-wash for paper is a non-issue unless maybe you develop prints in drums. In that case I could see some sense in the logic of warming things up to process temperature and preventing e.g. marks from stray droplets of water remaining in the tank rolling off the paper.

Stop! Bath…

A stop bath for color film and RA4 paper is in my view a good idea, although not strictly necessary. I prefer to use one, and simply buy cleaning vinegar, which is around 7% acetic acid where I live. I dilute this 1+10 or so and discard after a session, or perhaps replace even during a very long printing session. The logic behind stop-bath is twofold: firstly, it helps to immediately stop development, so that the development time is controlled more precisely. Hence the name.

Secondly, a stop bath prevents developer from carrying over into the bleach (film) or blix (paper). Developer is alkaline, and bleach is acidic, and if there is a lot of carryover and perhaps a poorly replenished bleach or blix, the pH of the bleach or blix will rise too much. This will result in reduced effectiveness of the bleach/blix and possibly problems with unwanted dye formation (fog).

When using a big-brand (Fuji, Kodak, Champion etc.) chemistry set, the bleach or blix will survive typical carryover of developer just fine as long as you replenish the bleach/blix properly. A stop bath can help the bleach/blix to function optimally, but it’s not strictly necessary. Carryover of stop bath (dilute acetic acid) is not a problem for bleach or blix and in fact will help it to maintain its low-ish target pH (ca. 3.8-4.0 for bleach, ca. 5.8-6.0 for blix).

The carryover of developer must certainly be avoided when using an amateur chemistry kit that uses a potassium ferricyanide bleach (as I understand, e.g. CineStill Cs41). The problem here is that developer would be instantly oxidized by the ferricyanide bleach, and this would result in non-image dye formation, a.k.a. fog. A stop bath prevents this as it helps to remove the developer from the emulsion. It’s also a good idea to not add strong (mineral) acids to a ferricyanide bleach for the risk of formation of deadly cyanide gas, so after the stop bath, use one or two water rinses. Personally, I prefer to just use the more modern EDTA and PDTA-based bleaches and bleach-fixers sold by the major manufacturers. They are trouble-free, and the film and paper you buy are made with this chemistry in mind, and vice versa.

Wash now and then

Intermediate washes between processing steps don’t hurt and can help to keep the chemistry in optimal condition. Especially in a color negative process, bleach tends to carry over into the fixer. Since fixer and bleach are actually not very compatible, this results in degradation of the fixer. So adding a wash step (or two) after the bleach and before the fixer can help the fixer to be used a little more intensively – provided it’s properly replenished. An additional wash bath will optimize the fixer’s capacity, but it will not extend it.

Stabilizer or final rinse

Stabilizers, final rinses and conditioners for paper are these days partly a stop-gap measure to get away with insufficient washing, as is the case in e.g. minilab machines. RA4 prints don’t require a stabilizer if properly washed. Washing can be done by repeatedly soaking the print in consecutive changes of water. It doesn’t have to be a lot of water at a time – just submerge the print, ideally agitate it for a minute, and change the water. If you do this a couple of times (let’s say 4-5 times), it’ll be quite thoroughly washed.

The same is true for film, which (C41 at least) also does not require a stabilizer as such. Some people like to soak the film in a final rinse bath that contains a biocide, which should prevent fungus and bacterial growth under adverse storage conditions. The final rinse generally also contains a wetting agent that helps manage drying marks (calcium scale deposits). Most chemistry manufacturers offer a final rinse for color film as part of their kit, or as a separate item. I personally consider its use optional.

If you want to DIY a final rinse/stabilizer: mix photoflo (or any photographic wetting agent) as per its instructions with demineralized water, and add a few drops of a 10% formalin solution to this. Soak the film in it for a minute, with agitation. Hang up to dry. Don’t was after this bath; it should be the final bath of the processing sequence. The formalin will act as a dye stabilizer and will bind to the gelatin and kill any bugs – it’s a very effective and durable biocide. The photoflo will help the water drip off of the film, reducing the risk of drying marks.

Challenge #6: Making it last

And when all is said and done – how to store this stuff in such a way that we can make it last as long as possible? It’s a combat against deterioration, and this means fighting three factors in particular: exhaustion, oxidation and crystallization.


Exhaustion of the chemistry occurs through regular use, as the important components of the chemistry are used up (developer, bleach), or as the chemical baths become saturated with byproducts (developer, fixer) that get in the way of good film or paper processing. The easiest way to deal with this is to either prevent overuse of the chemistry, and through replenishment.

For home-oriented chemistry kits, guidelines come with your kit on how much film or paper can be processed with each bath. Sometimes, especially for color developer, this will come with instructions for extended processing times as the chemistry is used for more and more consecutive roll. For instance, the manual may suggest to extend the development time for a C41 developer by a certain percentage for every two additional films processed in the same developer.

I’m personally a bit skeptical that such “stretch it as far as you can” processing will really yield perfectly consistent results. If you process let’s say 20 rolls of film in a liter of C41 developer, extending the development time as the manufacturer suggests, I expect that the last roll will have differences in color balance compared to the first one.

For home use and film that’s intended to be scanned and digitally color balanced, this may not be a concern and the savings of getting the most use out of the developer may balance out with the slight drift in processing quality. For those who prefer optical printing and want to limit processing drift to the absolute minimum, I think a different approach is more sensible.

Moreover, minilab chemistry generally doesn’t come with instructions on how to use the same small batch of developer over and over again, extending processing times as more film is run through it. The simple reason is that commercial processing lines just don’t work that way; they rely on replenishment and monitoring (e.g. pH and density measurements and control strips). Thus, the instructions for such chemistry will contain guidelines for replenishment rates instead, and for target pH and density measurements of processing baths. For RA4 developer and blix and C41 bleach, I just follow the replenishment guidelines and this keeps me from exhausting the chemistry.

As remarked earlier, I personally prefer to use C41 developer and C41 fixer only once or twice so that I remain firmly within the maximum capacity. Especially if you do several processing runs a week, I can imagine that you might want to try a replenishment system for C41 developer and fixer as well if you want to minimize costs. I haven’t tried this (yet) with developer, so can’t comment on its feasibility, but I suspect it’ll work OK if you observe good storage practices between processing sessions. For fixer, it’ll work just fine.


Oxidization, simply put, is the deterioration of chemicals due to exposure to (in particular) oxygen. Oxygen from the air tends to dissolve in the watery processing baths and then react with for instance developing agents (CD3 in RA4, ECN2 and E6 developers, and CD4 in C41 developer) and with fixer (ammonium thiosulfate). Bleach is resistant to oxidation – in fact, it likes to be oxidized as it’s part of its regeneration process. So the concern is limited to developers, fixers and also bleach-fixers due to their fixer component.

To an extent, the problem of oxidization is prevented by the composition of the chemistry itself. For instance, C41 developer usually contains a so-called ‘oxygen scavenger’, hydroxylamine sulfate. RA4 developer may contain the same (e.g. Fuji CPRA developer), or something similar. Fixer generally contains a large amount of sulfite, which acts in a similar way.

The problem with these preservatives is that they are sacrificial: they work by reacting with the dissolved oxygen, but break down in the process. So if oxygen keeps dissolving in the processing liquids, at some point the protection wears out and the developer or fixer start to deteriorate. At that point, the activity of the developer or fixer will start to drift and undesirable side-effects start to occur, and the chemistry has essentially become unusable.

The most straightforward way to prevent all this from happening is to limit the amount of oxygen that can make its way into the solutions. This means storing the solutions in well-sealed containers that are impermeable to oxygen. Suitable materials are glass and aluminium-lined collapsible wine bags/bladders. PET should work as well, but LDPE is a non-starter (actually, RA4 developer will dissolve it!) and even HDPE allows a little oxygen to pass through in my experience.

C41 developer, at twice working strength (an experiment) in entirely full glass bottles.

For fixer or bleach-fix, I personally find HDPE acceptable, but for color developers, I prefer glass. I’m trialing collapsible wine bags, but so far, I find glass bottles to be more convenient, although they take up a little more space. I keep a selection of bottles around, ranging in size from 150ml to 1000ml. I usually use volumes of 150ml or 250ml of developer at a time (Jobo rotary processing). Whenever I open a large glass bottle of stored developer, I take out what I need for the session and decant the remaining contents into smaller bottles. In doing so, I ensure that I always end up with bottles that are filled to the rim so there’s no air on top. Stored this way, color chemistry keeps well for at least a year and usually more, in my experience.

Storing concentrates or working strength?

The chemistry you receive from your supplier comes as concentrates that need to be diluted and sometimes mixed together from different bottles to make a working strength bath. This gives you two options for long-term storage: store the concentrates, or store the mixed and diluted working strength solutions.

There are different lines of thought about this. Rationales for storing concentrates include the smaller volume (saves space) and the fact that the manufacturer chooses this way of confectioning, so logically the chemistry should keep well this way. This still leaves the problem that if you open the bottles and take out part of the contents, you break the hermetic seal and possibly the oxygen-free atmosphere inside the bottle, exposing the contents to oxidization from that point onwards.

The sensible solution in my view is to decant the contents of opened containers of concentrates into smaller, glass (developing agents) or HDPE (other stuff) bottles. Some of the concentrates are sensitive to oxidization and perhaps even exposure to light (RA4 developer). They are typically the concentrate parts of the color developers (usually the smallest bottles of the set, with a pale straw or pink color), and to a lesser extent fixer concentrate. Keeping these under air-free conditions is essential.

Other concentrates, such as bleach concentrates, or the other parts of developers that do no contain the actual developing agents, are not very prone to oxidization – or sometimes not at all (bleach). For these concentrates, it’s not so critical that they are kept in oxygen-free conditions and it’s OK if you end up with partially filled bottles sitting around for a couple of weeks or a couple of months.

The other route is to make up the processing solutions to working strength and storing them that way. In particular for C41 developer, the rationale here is that in its mixed form, the preservative (the aforementioned hydroxylamine) is mixed with the developer and thus it can do its work. In the concentrates, the preservative is usually in a different bottle than the developing agent it is supposed to protect, because they’re not compatible in very high concentrations. Note that e.g. Bellini has worked around this issue by making a less concentrated ‘concentrate’ for their C41 developer, which can then be distributed as a single concentrate instead of (typically) 3 separate concentrates for just the developer.

Personally, I choose for the reason mentioned above to mix my C41 developer all at once and then store it in entirely full, tightly capped glass bottles. My experience with the Fuji minilab C41 developer is that it keeps for far more than a year this way without noticeably deteriorating. For bleaches, fixers and bleach-fixers I don’t really see the point in storing the larger working-strength volume, so I keep them as concentrates. With RA4 developer, I only mix my working strength batch of ca. 2.5l (which fills my RCP20 and is ample for the occasional tray development session) and keep that in entirely full PET soda bottles, and the remainder I keep as concentrates in entirely full glass bottles.

How do you tell if something has gone bad? Usually, the chemistry itself will show hints before you notice problems with your processed film or paper. Look out for the following:

  • C41 developer in working strength: if its color starts to turn from pale straw to pink, it has started to oxidize. Any color that could be described as ‘intense’ or ‘dark’ is absolutely not good. Note: this is for unused developer. Used developer can have funky colors due to anti-halation and sensitizing dyes from the film. For instance, Kodak Portra films in 120 and sheet film formats will release a very dark dye. It doesn’t mean your developer has died instantly. It’s likely still usable, but once this happens, ito of course becomes impossible to tell if the developer is oxidizing. 35mm color film tends to release more subtle magenta dyes.
  • C41 developer concentrate: if you have a 3-part concentrate, which is typical, there is one particular bottle with the developing agent that will go bad at some point. This may take months or (if you’re lucky) over a year to happen, but it inevitably happens at some point, even in factory-sealed bottles. The contents of the bottle will go a very deep purple that looks pitch black unless viewed against a bright light source. At this point, it’s toast. The other concentrate bottles may still be good. If you have some dry CD4 powder (it’s available through a few specialized sellers of photochemistry such as Suvatlar in Germany and Artcraft in the US, and through eBay), you could try mixing the working strength developer using the remaining bottles, and then adding 4.5g to 5g per liter dry CD4 powder of working strength developer instead of the contents of the developer concentrate. This is experimental and no guarantees that it will bring your C41 developer exactly “on spec”, but it should at least work.
  • RA4 working strength developer will oxidize and throw down a dark brown to black powdery precipitate that tends to stick to the walls of the container it’s in. In theory, this is bad news, but in practice, I always see this in my work batch of RA4 developer unless it’s super fresh, and it always just works fine as long as I replenish it. Mix fresh developer if it freaks you out, or just monitor the performance of the developer and accept it as one of the many imperfections of life in the darkroom.
  • Bleach concentrate or working strength: does not go bad in my experience. Keeps indefinitely in either form, so unless you intentionally destroy it by chucking other stuff into it, it’ll live.
  • RA4 (or C41) bleach-fix/blix: this is an inherently unstable mixture, because the requirements of a bleach are in some ways the opposite to the requirements of a fixer. Fixer breaks down when oxidized, but bleach thrives on it. In practice, a blix may keep well for many months if used regularly and replenished adequately. But at some point, it will start throwing down a pale yellow, very fine precipitate. This is sulfur resulting from the thiosulfate fixer breaking down. Discard the blix and mix a fresh batch.
  • Fixer, working strength or concentrate: this tends to keep very long, especially the concentrate, in air-sealed bottles. Typically it’ll remain good for several years. But sooner or later, it will ‘sulfur out’ just like blixer does by precipitating out a very fine white to off-white powder. This tends to cake against the walls of the bottle. It’s best to discard it at this point and buy or mix fresh product.
The way of all flesh…a factory-sealed bottle of C41 developer concentrate gone bad. The contents are supposed to be nearly colorless. It’s now pitch-black. This is completely oxidized CD4 developing agent.


One mode of deterioration I did not mention in the list above, but it’s common: crystallization. Especially in concentrates, it happens from time to time, and the cause is basically the nature of a concentrate: it’s very concentrated (no sh**, Sherlock!)

Concentrates are a balancing act between trying to make a product as compact as possible (leaning towards a high concentration) and the chemical limits to how much solids that will dissolve and remain dissolved in a liquid. This solubility limit varies strongly per chemical, but also depending on storage conditions. Specifically, the lower the temperature, the lower the solubility limit. As a result, if you keep concentrates of e.g. developers in an unheated attic, shed or garage, it’s possible that they will crystallize out on cold days.

Crystallization due to low temperatures is often reversible. Just heat up the concentrate, swirl it a bit and wait patiently for the crystals to dissolve. It often happens by itself as winter gives way to spring, everything warms up a bit and everything goes back to normal.

However, not all crystallization is reversible. Especially monopart RA4 developer concentrates (Fuij MP90 for instance) in my experience can crystallize out under certain conditions and at that point, there’s no going back. Most of the crystallization will be the carbonate activator, and since there’s a lot of it in a developer, I often just accept it if there’s a bit of crystallization instead of chucking out the concentrate. It’s a bit haphazard, and if you’re more exacting and diligent than I am, discard the crystallized concentrate (if it doesn’t re-dissolve upon heating) and purchase a fresh batch. The good news is that it tends to take a very long time for this to happen (over a year).

Crystallization in an old bottle of Fuji MP90 RA4 developer monopart concentrate. Broken up crystals can be seen floating around. When left undisturbed, the crystals tend to grow very pretty and big.

A special case is RA4 bleach-fix or bleach concentrate, which apparently can crystallize out spontaneously. This is not something I’ve actually seen happen yet, but I was warned by a Fuji engineer about it. The remedy is very simple: agitate the bottle once in a while. This will apparently stop the process of nucleation. It’s a bit like the big walls of paint bottles in an auto paint shop that are swirled every once in a while to keep the pigments from settling.

Well, that’s enough for now to take in. As said above, it’s a lot of information, but from a darkroom user’s perspective, it’s not all very complicated. Yes, it gets complicated if you drill down into the underlying mechanisms, formulations etc. If you find that sort of thing interesting, by all means indulge! But if you just want to develop your film and prints and be done with it, rest assured that you can do this. You’ve got this.

Work with whatever products you can get your hands on. Follow the instructions of the manufacturer. Use common sense. And ask someone if you’re unsure. I can recommend the Photrio forums, which I feel are the best place (bar none!) for amateur photographers to ask technical questions. And always feel free to reach out to me by commenting on this page or contacting me directly.

One thought on “Who’s afraid of cyan, yellow and magenta? Using color C41 and RA4 chemistry at home”

  1. I use Bellini RA4 kit and I reuse the developer several times. I think too much. So, I´ve been thinking to use Fuji Hunt. You know, the money. This is the information that I need it.

    Thank you very much for the information.

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