How to Test Your C-41 Film Chemicals

Avoid Disasters and Maintain Quality Results With a Simple Snip Test

3 min read by Dmitri.
Published on .

Developing film with chemicals is like cooking: you must measure everything and apply a technique. But sometimes, you also have to check if what you’re cooking with is still good.

There are many ways to identify expired food (i.e., smell), but when it comes to film, there’s a process you need to follow to verify if your chemicals will develop your images and not ruin them. Thankfully, there are shortcuts to help you do this quickly.

C-41 colour negative process is the simplest way to develop film at home. But it can still fail if the chemicals are exhausted or expired. Depending on how many rolls of film you develop at once, this can spell disaster (blank rolls) or gradual quality degradation that you can only spot after scanning your first frame.

A snip test is a simple and quick way to spot issues with your chemicals. There are a few ways you can perform it, depending on the degree of confidence you’re looking to get. The simplest method requires minimal setup and can be done in a fraction of the time it takes to develop your film.

How quickly to test C-41 film developer.

Setting up a water bath, warming the chemicals, drying film, and scanning can take a while. Thankfully, you don’t need to do any of these to check if your developer works.

The simplest way to test your C-41 chemistry is to pour some developer into a clear jar or a cup and drop a small piece of fresh film in it. There’s no need for a light-tight tank — a snip test should be done in daylight. Typically, you can snip/clip a piece off the end of your freshly-exposed roll (as you would anyway before loading it in your Paterson tank).

There’s no need to heat up or precisely time your development time. I used my disposable bamboo chopsticks to swirl my film around in the jar (which I discarded after). It takes about five minutes (3 min swirl, 2 min dry) to determine if your C-41 developer is still good:

If the film clipping is the same shade of black on both sides, the developer is OK.

⛔️ If the film clipping is lighter on the underside and isn’t completely black (i.e., it looks similar to how it did before dipping in the chemistry), the developer should be retired.

Of course, this quick test won’t tell you how well your developer works — just whether it’s usable.

You can track your developer’s performance by heating your chemicals, timing the process, and agitating your snippet as you would while developing film. You’ll need to do this immediately after mixing your fresh batch of chemicals to create the first snippet — an “ideal” version. File it and use it to compare with the subsequent tests. As your developer exhausts, your snips will get lighter. You can use this information to adjust your timing or to decide when the chemicals are no longer usable. Consistency and diligence are essential if you want reliable results.

How to quickly test your blix chemicals.

Your blix can be tested using the same process as described above: dip your (undeveloped) film snip into the blix mixture for a few minutes and see if it comes out clear. You can formalize and extend this process by timing, warming, and agitating the chemicals and then comparing them against the first test — the same as you would for the developer.


Spending an extra few minutes before developing your film — especially if you haven’t done so with the aging chemicals for a few days or weeks — can help you save your images from a disaster. Blix and developer can expire or exhaust, which is a gradual process. The worst-case scenario is contamination that may happen unexpectedly (even when you think you did everything right). Contaminated C-41 chemistry will yield you a blank roll. A simple snip test can easily prevent this.