One of the most complicated parts of getting started in screen printing is the creation of a light-safe environment. Screen printing darkrooms are a necessary feature of any screen shop, so let’s dive in to what you need for a good one.

Type of Light

Emulsion exposes in the near-UV spectrum of light, in the 310-420 nanometer range. To avoid any exposure, you want to avoid unexposed emulsion getting hit with this light. Generally, this means that you want a yellow light – often sold in home improvement stores as bug lights, or a yellow fluorescent tube cover.

Some LED lights might work as well, but be sure to read the technical sheets to make sure they don’t emit light in the 310-420 nanometer range. If you can’t find technical information, assume that it is not safe for your darkroom.

The good news is that the amount of light doesn’t matter – only the type of light. You can have a very bright screen printing darkroom provided you are not emitting any light that will expose your screen.

Humidity

Emulsion is hygroscopic, which means it likes to soak in the moisture that is in the air. If you have too much moisture in your emulsion, you can run into issues with inconsistent exposure, premature breakdown, and ruined positive films. Keeping your humidity below 50% is good, but your ideal darkroom humidity should be in the 15-40% range. In some climates you may need to invest in a de-humidifier to be sure to have the air within spec. A hygrometer to measure the humidity is an inexpensive investment.

photo of a hygrometer
A hygrometer is an inexpensive investment that will help you create better screens.

It's Good to have Two Darkroom Spaces

As mentioned before, unexposed emulsion should never see the light of day. After you have coated, dried, and exposed your screen it’s time to wash it out. You still have unexposed emulsion that you want to keep that way until it’s washed out, so it’s really great if you can have your screen room divided in two sections: one dry area for coating and drying your screens, and one area for exposing and washing out your screens that’s going to end up being more humid.

Coating and drying screens should take place in the driest atmosphere you can create. Washing out your screen is invariably going to increase the humidity in that environment – so two spaces makes it so you can have an ideal environment for your screens.

If you can’t make two separate spaces, try to separate out your screen coating and drying time from your screen exposure and washout time. The best way to go about this would be to expose and wash out screens in the morning and then coat and dry your screens overnight.

Conclusion

The darkroom is one of the most challenging spaces to set up when you are getting started in screen printing, but arguably the most important. Without a darkroom, you will run into issues of screens exposing prematurely – or even worse, buckets of emulsion exposing prematurely.

For more information visit the Midwest website, or contact your local sales representative.