C41 Home Processing - my take on the best practice and lowest cost

[garry611]

I will address what I believe is the best and most economical c41 processing at home in several parts. I split this into several parts since the explanations are long and I hope that this might prove to be helpful to anyone processing c41. I decided to post this after talking to someone who wasn't even aware of how we really reached this point with c41 processing over the years. In the past, I processed c41 at home for a long time, then the chemical cost and availability became problematic- very expensive and only available in large quantities or volumes. Seemed to be only mini-lab sizes. Kodak did have some reasonable developer kits but bleach was a very high cost in the process. This is no longer the case with some of the kits available today- Arista or Cinestill. But how to use these smaller kits and keep expenses low is addressed hopefully in these several parts. If what is working for you now is acceptable, no need to change. But there may be a less costly method.

Part 1 History
I worked in a film processing lab in the 60-70's, well after the conversion from c22 to c41. The film processor tanks, at the time, each held gallons of c41 chemicals. The processors were large tanks with plastic rollers which the film ran over thru the solutions. There was a 35mm leader (a film with the same dimensions of 35mm film) that snaked its way thru the processing rollers that were submerged in the processing tanks. In the darkroom, each exposed roll of film was taped together, with a unique number on the tape for identification, end to end to the next exposed roll creating in effect a long roll of 35mm film consisting of many different exposed rolls - approximately 30-50 rolls of customer's film. At the end of this roll, another long 35mm leader of correct length was taped which would remain in the processor for the next days run so the new long roll of exposed film could be taped to it, as a continuous loop. After the current day's large roll of multiple exposed rolls was assembled, it was taped to the film leader in the processor. Then the processor was started and the film would be pulled thru the various tanks over the rollers submerged in the tanks. At the top of each tank where the film emerged before going into the next tank was a squeegee to remove any chemical carryover. Hence the lines on the films if the squeegees where not cleaned correctly. The speed was set so the film entered the dev chemical tank and exited thru the squeegee after 3:15 min. There were more rollers and a longer tank for the bleach so the film remained moving in that chemical for a longer period of time. The important point to all of this is that the processing time could not be extended in any one bath. If the bleach tank was too weak, the film still exited under bleached, within a set time, due to the film continuously being pulled thru the rollers at a constant speed. At some point over many weeks, if it was determined the tank activity could not be effectively adjusted anymore - the entire chemical tank was dumped, and a new working tank solution was made. Since it was a volume of gallons, it was costly so the tanks were adjusted and used for as long as possible.

Since the chemical tank volumes were so large, 30-50 rolls of film, going thru in one day, did not have a huge effect on the overall processing activity. After the completion of the long roll of film, the tanks were covered for the night. The next day, the tanks were uncovered and topped up with water for any overnight evaporation, and then evaluated if any additional chemicals needed to be added to bring the tanks back to correct activity. Since the chemical tank's volumes were so large, minor inaccuracies in chemical additions, did not have a large effect on overall processing.

Apparently, Kodak had tested and selected the best time and temperature for the film to be processed in the least amount of time to maximize the film through put, and with the least amount of color deviation if the chemical activity was not 100 percent. That is how the processing times were established, I believe.

Then, after years, came the Mini-Labs. The mini indicated that the overall processing tanks were much smaller. This basically reduced the working chemical tank volumes from gallons to liters. The smaller tank volume reduced the cost to dump and refill the tanks whenever needed. However, with the smaller tank volumes, one chemical adjustment per day was not practical. As the film went thru the chemicals, activity changed more quickly due to the smaller tank volume, so there was a replenishment done after each roll of film to keep processing activity correct. Since the replenishment addition was so small, it was automated so it could be easily controlled. The processing times and temperatures remained basically the same as the large volume tanks. Some companies came out with different formulations to speed up the overall processing time and some processors had the ability to modify their procedures.

Then Jobo came out with even smaller processing systems, the ATL and CPE. Kodak and others made smaller kits (1 L or 5L) to accommodate these processors. However the chemical volumes of 1L, did not lend itself to replenishment since it was too difficult to control the accuracy and chemical instability occurred more quickly due to small volume, so one-shot development was used. An important point about the Jobo or manual processing was that the time in each solution could be controlled individually as opposed to the automated processors. This allowed more flexibility with solution processing times. So if the bleach is slightly weak a longer time can be utilized so bleaching can go to completion. Realize at some point, the bleaching activity is neutralized and no amount of time will allow the bleaching to go to completion.

In the next part, I will discuss my opinion on the small processing kits that are readily available.

 

[garry611]

Part 2 Color developing Kits
I have attempted mixing c41 developer from scratch and have it perform well without much luck, and the individual chemicals required in small quantities is not cost effective, at least for me. The small c41 kits, in my opinion, is the best option. There are several small c41 kits available but I've limited my discussion to basically two main liquid kits - Arista and Cinestill. The reasoning is that in reviewing the MSDS for many kits, only these two kits are low in price and list CD4 as the color developing agent. These two kits typically come with a three part mix for the developer. And they are liquid components which allow mixing different volume amounts rather than a powder kit (which may have a longer shelf life until used) but requires one to mix the total volume initially. I looked at the Bellini kit as they have available a separate developer only but it is supplied in one bottle and does not seem to be CD4. Although Bellini may be a better alternative since it may be more stable, I omitted the Bellini since it may be using something other than CD4 as the developing agent. I intend to try this in the future although with components from other kits which is explained later.
There is an advantage to the Cinestill kit as the c41 developer is available as a separate powder packet without the other solutions. This permits replacing the developer at a lower cost since you are not replacing all the processing solutions.
With either liquid kit, mixing developer with the proper ratios, you can mix 500ml or 1000ml depending on you needs. Distilled water is always recommended for the developer.
The best storage containers for the developer are PET plastic bottles with the softer plastic caps as these can be squeezed to remove the air and the cap creates a very tight seal.
So with either kit you can obtain 500m (2x) or 1000ml (1x) of c41 developer.

Each of the two kits have Blix components for bleaching and fixing of the film. Blix solutions have a limited life since once they are mixed. Blix will go to exhaustion over time even without use. However, the bleach solution has an almost indefinite shelf life when unused and a very long processing life when used. A straight c41 bleach only solution can be regenerated by aeration which is bubbling an aquarium air stone in the solution. It isn't prone to oxidation, in fact, it's almost the opposite. So if the bleach is used as a separate individual processing step, without the addition of the fixer, it will not quickly exhaust. When it is used in processing, the bleach solution deteriorates mainly due to contaminant build up from the c41 film.

So what needs to be done to use the bleach solution by itself. For the bleach to be active, it has to be acidic, at a pH of around 5.5 pH So if the dark colored bleach from either kit is taken and adjusted to a pH of 5.5, you would have a bleaching solution that should have a long shelf life. I believe there is a separate thread on separating the fixer and bleach on the forum. There are limited range pH test stripes available which allows pH measurement without the need for a pH meter. The pH isn't terribly critical as long as it is acidic. Some kits come with an acetic acid solution exactly for this purpose but you probably should not use the whole bottle to change the pH of the bleach since this was to be used when the fixer was added.
In addition to being acidic, the bleach solution needs an excess of bromide, so 50-100 grams of sodium bromide has to be added. Again, the amounts are not critical, the excess bromide allows the AgBr to form during the bleaching process. Sodium bromide is inexpensive from any photo chemical supplier.

To recap, take the dark colored beach solution from the kit, add water to 900ml, add 50-100g of sodium bromide, and adjust the pH to 5.5, then add water to 1000ml. This will give you a long lasting bleach solution, to regenerate bubble air into the solution for 15-20 min before use. I take a two liter soda bottle and drill to holes in the cap, one for air to escape and the other for the air tube to enter with the air stone at the end to drop into the solution. Before I'm ready to process, remove the solid cap and replace it with the air stone cap and start the air pump while the water bath is heating and films are loaded.
Now how do you address the contaminant issue from using the bleach. When you purchase the next kit, take the bleach solution from that kit into 400ml and add 50-100g of sodium bromide, adjust the pH to 5.5 and add water to 500ml. Call this your bleach replenish solution, and add 20ml of the replenisher after each use. This should allow you to use this replenisher at least 25 times. In the end you will have replaced half the total bleach solution with fresh bleach replenisher. This is very similar to the Kodak bleach replenisher process.

The Fixer bottle from the kit is not used and is replaced by a separate fixer. It is replaced by TF-5 fixer which is a B&W fixer that is neutral in pH and will not bleach the colored dyes. This is very inexpensive - it is diluted 1:4 and the capacity is 15-20 rolls of film of working solution. So a liter of the TF-5 fixer will process 120 rolls conservatively. It could be made fresh for each development run. The stock fixer can also be mixed as a separate fixer for B&W films but it is not advisable to use the same TF-5 fixer solution for c41 and B&W film, better to have separate solutions for each.

In the next part, I will describe a general processing routine that can be used.

So after the initial setup, the only replaceable processing chemistry on a regular basis is the color developer. The color developer can be monitored and if stored in PET bottles, will last much longer than their suggested exhaustion time. There is less chemical effluent in the overall process, and the cost is cut in half by only having to purchase the developer as a separate package after two regular full kits. The separate bleach and fixer as separate solutions is more active than the blix solution and will go to bleach and fixation completion with more certainty.

 

[koraks]

I omitted the Bellini since it may be using something other than CD4 as the developing agent.

I don't think so. I've gone through a fair share of Bellini MSDS's and they seem to be doing things by the book. Replacing CD4 with something else would be waaaay out there.
Indeed, this from Bellini's C-41 developer MSDS:

That's CD-4 just fine.

Cinestill on the other hand has been known to cut corners in their Cs41 chemistry, especially the earlier versions, but appear to have changed to more conventional formulations some time ago.

It isn't prone to oxidation, in fact, it's almost the opposite.

You can leave out the "almost". Well, it is prone to oxidation, but it's actually a good thing here, as opposed to developers and fixers.

50-100 grams of sodium bromide has to be added

I don't think you want to add so much sodium ion to a bleach. The correct substance to use is ammonium bromide. It's nasty, and more expensive than either sodium or potassium bromide, but should be fairly easy to get, still. The problem is reduced bleach speed and effectiveness, resulting in a risk of retained silver, which will wreak havoc on gamma/contrast. You may never notice it when you scan apart from slightly grainy negatives, but it'll be a b*tch if you ever try to optically enlarge your film. See comment by Photo Engineer here: https://www.photrio.com/forum/threads/c41-bleach-formula.12343/post-171034

The Fixer bottle from the kit is not used

Why not?

will not bleach the colored dyes

The problem with leuco dyes is virtually impossible to reproduce with modern C41 films. It's evidently fine to use a pH-neutral fixer, but don't sweat it if it turns out to be an acidic one. The dyes will be colorful just fine. Technically, 'bleaching' is not the correct term BTW. Dye hue of the old color dyes was pH-dependent; they didn't bleach as such, they just appeared differently depending on the pH of the environment, a bit like litmus paper.

The color developer can be monitored and if stored in PET bottles, will last much longer than their suggested exhaustion time.

This is certainly true and overall I agree with your approach of using a (quasi-)replenished C41 process. Personally, I use minilab chemistry to keep costs down. It lasts a loooong time so the larger volume doesn't hurt, and it comes with replenishment data which is convenient for the bleach. I use fix one shot at a weaker dilution most of the time, replenish the bleach and use the developer one shot at official dilution (with starter etc.) This is all similar to what you're doing apart from fixer reuse (which is fine, really) and the addition of sodium bromide to the bleach (which I would not recommend; see above).

 

[garry611]

Thank you for the comments. I usually scan the negatives so that gives some leeway for corrections, if needed. The intention is to keep costs as low as possible, thus the use of sodium bromide. Ammonium bromide is substantially higher in cost. Unfortunately, PE doesn't address what 'very slow' actually means. If it requires a bleach for 15 minutes versus 5 minutes, for example, I have the time. Often I find some suggestions seem to be contradictory without a further explanation. This isn't meant to be a negative reflection on the PE post. But in the same post, PE says that the ammonium sulfite 10g can be replaced by sodium sulfite. Although this is at a low weight of 10g, I'm not sure if 40g more is that detrimental. The formula listed requires 150g of ammonium bromide. I would anticipate 150g of sodium bromide would have large effect on bleach speed. No doubt ammonium bromide would be the better way to go if the addition cost doesn't matter.

 

[lamerko]

Because I mix chemistry at home, I do various thin calculations of how much it comes out.
Regarding the C-41 process - I use bleach for minilabs which is very cheap per roll. I don't like blix and try to avoid it whenever I can.
The cost of chemistry for C-41 developer comes out to EUR 3.58/liter if I follow all the ingredients, EUR 2.86/liter if I omit DTPA. Without HAS, it comes out to €2.42 if used as a one shot. The most expensive component is CD-4, which costs 24 euros for 50 grams. The costs would drop a lot if I ordered at least a kilo from China, as I did with the CD-3.

 

[garry611]

In the States, obtaining individual color chemicals over the years has become more difficult due to regulations by the government. There are a few suppliers but the cost to acquire would be more than the total premade kit. At least that is my opinion, it is the legal restrictions. So I tried to stay with a total package concept that is easily obtainable but modify it slightly to reduce ongoing costs. I still mix my B&W from scratch as these photo chemicals are more readily available. Perhaps if more people swing back to darkroom processing, more options will become available.

 

[lamerko]

This with the regulations is really unpleasant, but surprisingly, there are no components under regulation in the formulas for C-41 developer. Most chemicals are widely available household and inexpensive. I look at the prices in Artcraft - they are better than in Europe. It would be cheaper for you