2016 March 25    Film   Developing


C-41 is the standard process to develop color negative film.  It's often said to be more difficult than black & white film developing, but I've found that it's quite easy. It can be lots of fun, too.

I've shot rolls and rolls of color film over the years, but it took me this long to start developing color film myself.  It's a learning process for me, but with my chemistry background maybe I can offer some useful insight as we go along.

Let's see.

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In This Article


Gearing Up


Temperature Control

Mixing The Chems



Blix and Wash




Handle the chems properly and follow the safety instructions included with the kit.

Like most chemicals, they require eye protection.  Avoid getting them in your eyes.  And obviously you should also avoid ingesting them.  They could be harmful, possibly even fatal if swallowed in quantity.  However, that's true of many things, including detergents, automotive fuels, hair care products, paints, etc., etc. 

I would also highly recommend gloves.  Nitrile gloves are cheap and widely available nowadays.

Use containers that cannot easily be mistaken for food or drink.    Store them out of reach of children.  Be sure to read the other precautions that are included with the kit.

Gearing Up

Obviously, you'll need a C-41 developing kit.  This contains a few different packets of powdered chemicals, with instructions for mixing (etc).  To get your own kit, this link should have it (last I checked, also the best deal around, or close to it);  if not, try this link or this one.

You'll need the developing tank, a funnel, and the basic measuring wares for liquids.  These are the same things talked about in the Black & White Film Developing article.  Be sure you have a 1000-milliliter graduated cylinder.

It helps if you have a portable cooler, something like this one.  You'll need room for three or four one-liter bottles and a lot of water.

If you don't have a cooler, a stock pot works well.  Here again, it should be able to hold three or four one-liter bottles.  The depth should be enough that the bottles can be immersed in water almost up to the caps.  (Try for at least 3/4 of the way).  The stock pot method uses up more hot water, but it's a bit easier.

Don't forget the thermometer.  You'll be dealing with temperatures of 100 to 110 F, maybe higher when you're testing the tap water.  A thermometer very similar to this one has worked well for me.

For a "one-liter" C-41 kit, you'll want three or four one-quart containers to store the solutions.  Try this link or this one for the bottles.  Again, don't use food or drink containers, even if the labels were removed.  Get containers that cannot be mistaken for food or beverages.

Your chems will last longer if the containers are amber-colored.  Opaque ones are a plus.

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In B&W film developing, it's easy to mix up half a liter of chems at a time.  You can develop one roll of 35mm and then change the formula for another roll, if you want. 

C-41 could probably be run like that, but there would be some waste.  The biggest waste, actually, would probably be the fixer / blix.  That's because the main ingredient in fixer will lose effectiveness quickly when diluted.  It actually self-depletes.  (B&W fixer is cheaper, so it's not as big a deal to waste some.)

Some people have noted that maybe the powders don't have all the chems uniformly-distributed throughout;  the kits were designed to use the whole packet.  I don't know how much of an issue this would be;  scaling down B&W fixer seems to work OK, but then again the results are kind of erratic unless you use an excess.  So maybe they've got a point there.  If you could figure out a way to sample the powder while maintaining an accurate particle-size distribution, then go for it.

C-41 uses multiple colors, so that adds a special challenge.  The different reactions are probably going to have slightly different rate curves.  If I had to guess, I'd say the process was probably designed so they all intersect at a certain temperature and concentration.  Going outside the recommended parameters might cause color shifting and other "effects". 

The three colors are on different layers of the emulsion;  the yellow dye (top layer) is the most accessible.  Variations in procedure can easily translate to too much blue in the scans or prints.  As it is, scanning is already a challenge to eliminate excess blue-cyan, due to the negative stock color.

Figure on mixing up the whole batch and doing a lot of film developing for three or four evenings. 

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Temperature Control

B&W developing works great when the chems are at room temperature, 68 to 72 Fahrenheit.  That makes it easy; you don't have to heat or cool anything.

For Unicolor C-41, the ideal temperature is 102 Fahrenheit.  You can stray from that about two degrees either way.  Much outside of that, and color shifting might occur.  (Then again it might not; again, some people say they've gotten good results.)

The easiest way to maintain the correct temperature is to use "thermal mass". Immerse the solution bottles in water of the desired temperature.  I use either a cooler (see picture) or a large stock pot.  Remember that as the bottles warm up, they will take some of the heat from the water bath.  Therefore, replenish the stock pot or the cooler with warm water as the temperature drops.

Initially, figure on warming up the bath a little too much.  110 to 112 degrees would be OK in the beginning.  As the bottles begin to warm up, try to keep the bath at 102-104. 

The stock-pot method uses up more hot water, but it's easier.  Simply run water into the stock pot, as needed, to keep the temperature where you want it.  Once the chems are up to the temperature, everything should stay there for quite a while.  If you see the temperature falling too quickly, it probably means the chems are still warming up in the bottles.

You're supposed to keep the developing tank in the warm water-bath, but I don't.  A metal tank might need the bath;  the plastic one appears to do OK without it, for the most part.  If the room is really cold, though, it could lose too much heat during the developing.

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Mixing The Chems

You'll have to make sure everything is correctly mixed, at the correct temperature, and sitting where you need it.  This will all have to be in place before you try the process.  This may seem obvious, but it's so important.

If you have it, use distilled water.  Ideally you should de-gas it ahead of time by bringing it to a rolling boil and letting it cool.  When ready to mix, it helps if you pre-warm it to 110 degrees F or so.  The exact temperature is not critical.  Don't use cold water, though;  the powders won't dissolve completely, or they'll take forever.

It goes like this:  800 ml of water, then add the powders and dissolve;  finally, add enough water to make 1,000 ml total.  Don't add all 1,000 ml of water first and then add the chems;  that would cause the volume to exceed 1 liter.  In film developing, concentration is "amount of solute" relative to "total amount of solution".  That's an important concept.  (On a side note: it's why dilutions are more correctly thought of as a part-to-whole ratio, not a part-to-part ratio.... )

Make sure all the powder dissolves.  The Blix tends to have some undissolved solids on the bottom.  It all has to be dissolved, or the concentrations won't be correct.


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The Pre-Soak

Immerse the film in distilled water at 102 F for one to two minutes.  Tap water would probably work; however, I'm thinking it's possible that certain components of the developer and blix might be able to precipitate insoluble salts on or in the emulsion.  This could be at a nano-scale level;  you wouldn't see it, but it might affect the process in other ways.  Example: sulfite ---> sulfate ---> calcium sulfate (precipitate).  

I would just use distilled water if possible;  as I said in Mixing The Chems, pre-boil it.  Do this a few hours before you use the water. 

You can pour out the pre-soak when it's done.  It will have picked up some of the dye from the film stock.  I don't know if this is an anti-halation dye, but some black and white films behave the same way.

Be ready to go on to the next step immediately, because everything has to stay at the correct temperature.

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This step runs for three-and-a-half minutes at 102 F.  (Some kits say 3.25 minutes; the instructions I have for Unicolor say 3.5 for a manual tank.)

This is the most temperature-critical of all the steps.  You can run the developer at 100 to 104 F, but don't go outside that range unless you really know your stuff.  (Some people have run C-41 at lower temperatures, but the results weren't always good.)

The developer is also intolerant of contamination, as film developers generally are.  Soap, detergent, blix, or acidic materials (e.g., vinegar) could ruin the development.  Distilled water picks up some CO2 from the air when it's sitting on the shelves, making it acidic.  Remember that "stop baths" are acidic.... 

As mentioned before, I would boil the distilled water ahead of time to remove the CO2.  Let it cool in a covered metal pot.  Then, use that to mix up your chems.  I haven't tested to see how much effect the CO2 has, but I wouldn't be surprised if it caused negatives to be too grainy and dark (under-developed).

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Blix and Wash

Some C-41 kits have a separate "bleach" and "fixer".  The Unicolor kit combines bleach and fixer into one "blix" solution.  The recommended time at 102 F is 6.5 minutes.  As you develop more rolls, you'll probably have to extend that.

The combined bleach and fixer makes the process more convenient (fewer bottles), but it shortens the service life.

If you store the blix solution in the cold when not using it, you could probably get more than three days out of it.  Actually I'm finding it's good for quite a bit longer than that.

The blix contains iron (III) compounds, giving it a very dark color.  It smells like hair salon chems;  there's some ammonia there.  I do know that thiosulfates are not especially long-lived when they're in solution;  the blix will therefore lose its strength.  Again, it still lasts for a while, much more if it's cold-stored.

I found that it works just as well at t=24 hours as it did when t=0.  In fact it seems to work just as well 10 or 12 days later, as long as you didn't deplete the chems by developing too many rolls.  (Keep the blix well-sealed and cold when not in use, with as little air space over the liquid as practical.)

When the blix step is complete (6 1/2 to 8 minutes), do a wash.  For this, regular tap water should be OK;  by this point it should be less likely to cause a problem if there's any precipitation of calcium salts.

Wash for three minutes or so, using warm water (95 to 105 F).

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As with the other components, make sure you read the manufacturer instructions and safety warnings before mixing or using this.  (Stabilizer is not strictly necessary for C-41 films made since 2000, so you can just omit this step if you prefer.)

The stabilizer solution is not as concentration-critical as the others.  Simply mix the powder into 1000 ml of water.

Stabilizer can be at room temperature.  One thing I wouldn't do, though, is hit the negatives with cold liquid after they've been in warm.  I know with B&W that this can cause "reticulation", which is not good.  I've been keeping the stabilizer at the same general temperature as everything else. 

This step was designed to inhibit mold growth on the negatives.  Colorful dyes with no silver would provide a better growth substrate than B&W film.

You're supposed to leave the stabilizer on the negs, not wash it off.  Simply remove excess liquid and just let the negs dry.  First batch, I didn't do this; I actually rinsed 'em.  This could become a long-term experiment to see if any mold grows on the negatives.  Or, maybe one day I'll go ahead and soak them in stabilizer again. 

When the negatives dry, they'll have water marks.  Actually these may not be water marks, but instead hexamine, the stabilizer chemical.

Hang up the negs to dry.  Attach a clothespin to the bottom of each negative strip so they don't curl up when drying.  (Works equally well with B&W or color... :-D )   I don't usually cut the negs until they're completely dry.  Then, store the negatives properly and go shoot some more film!


This has been a look at developing color film at home.

Home C-41 is potentially much better than one-hour-photo labs;  some of these don't even give your negatives back anymore.  And sometimes, I think the one-hour labs are using chems that are near depletion.

How about pro labs?  The Unicolor kit combines the bleach and fix, which pro labs don't do.  However, I'm seeing results just as good as any pro lab that I've tried.  With some tweaking of the procedure, there's probably even some room for improvement.  Separate bleach and fix are supposed to give better results, but I haven't tried this yet;  would have to get the chems first.

Now that one-hour photo's been bean-counted practically to oblivion, color film developing could become part of the creative process, just as it's always been for black & white.  The C-41 process works best when kept within narrow parameters, but there's still push processing and other stuff.  Maybe in a future article we'll look at that in some detail.

One thing is for sure:  there's something almost magical about being able to develop your own color film. 

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