Cheat Sheet For Extending Unicolor C-41 Capacity

One day back around 2011, I went to my local thrift store on a tip from a friend that there was a bunch of darkroom equipment currently out on the shelves. I didn't expect much more than maybe some cheap 35mm enlarger or something but figured I'd go check it out anyways. What I ended walking away with for $30 was a Jobo CPE-2 system for processing color film and prints.

Jobo CPE-2. $30

If you're not up to speed on photography equipment, the summary you need to know is that this equipment still sells for way more than $30. Today in 2019, kits similar to what I got are actively selling for about $500 on eBay. A nice score!

Although I recognized the value of this piece of equipment, I never really used it as there was a lab locally that would process my c-41 film at a very reasonable price with an hour turn around.

Over time the quality of the films that lab was processing went downhill, and I reached a breaking point when somehow the end of almost every other roll of medium format film would get exposed to the light when during processing and it would ruin the first frame on the roll. This especially unacceptable when I started using the 6x17 format as ruining the first frame meant I was throwing away a quarter of the images on the roll.

Thus, I pulled the CPE-2 out of storage and got to work processing my c-41 at home. I've been using the Unicolor Powder C-41 Film Negative Processing Kit for my chemistry, and so far everything has been easy peasy. With the Jobo regulating the water and chemistry temperatures, it is no different or harder than the black & white film I used to process at home.

Some home-processed film

With a stated capacity of eight rolls per liter of the chemistry, the kit comes out to about $3.12 per roll. Slightly cheaper than having Citizen's Photo develop the film, but without having to wait a week to ship the film across the country.

But of course, the thrifty do-it-yourselfer's second order of concern is how much can this capacity be extended to drive down the costs?

Well. Luckily for us, other people have already done this legwork. The most comprehensive study I've found on extending the capacity of the unicolor powder kits has already been done by

I've only just begun with seeing how long, and now lazily I can store my chemistry and still get acceptable negatives. But what I want to share is a simple printable sheet that converts the formula provided via the link into an easy to use table to keep wherever you process your film.

Extending Unicolor C41 Capcity Sheet (Thumbnail)

Download Uncolor C-41 Extended Development Times Sheet

This should be straight forward, but if you need instructions, the first column is the number of the roll(s) to be processed that your batch of chemistry has seen. The second column is the adjust development time based on the formula provided at The third through fifth columns are there for you to either checkmark or timestamp when that roll of film was processed so you can easily cross-reference and get the next adjusted time the next time you process film.

No more needing to do math or remember how many rolls you've already processed! And with three big chemistry columns, you can go green and reuse the same sheet for three batches of chemistry!

*Extend your Unicolor chemistry capacity at your own risk.

Category Gear & Technique