Feeling Exposed?

Figuring out exposure times for your silk screens doesn’t have to be complicated. Follow these steps and avoid time wasting re-dos.

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When exposing a screen the time varies depending on the type of light, whether there is reflector, distance from the screen, bulb wattage, etc. If you don’t expose long enough the image gets washed away. If you expose too long, you will start to lose fine detail of the image.

What kind of light to use? I currently use two task lamps with large flood reflector bulbs in them. They are each 150 watts but they are florescent bulbs so they are only using ~40 watts for the same light output. They’re my attempt at being a greener screen printer. I used to use a professional unit that housed a single 1000 watt bulb but that unit is too big for my home based studio so it is in storage. Whatever you use, make sure you have some way of clamping the light source, or mounting it above the frame for an extended period of time.

*You can also use the sunlight to expose a screen. It will work even on a cloudy day since it’s the UV rays that harden a screen and not sunshine and UV rays pass through the clouds. 

I would strongly advise you to run a test to find the best exposure time for your screens and emulsion before you start shooting screens. To do that you will want to take the light you have, and place it above a frame that has been coated in photo emulsion (and has thoroughly dried in a dark cool area of your home or studio). You want to place it high enough that the whole frame gets equally exposed, probably about 12-15”. Once you have the light and placement figured out you’ll want to figure out some rough times. For a 150W clear incandescent bulb the following times might apply:
Screen size, bulb height, exposure time

• 8×10, 12 inches, 45 minutes
• 10×14, 12 inches, 45 minutes
• 12×18, 15 inches, 74 minutes
• 16×20, 17 inches, 92 minutes
• 18×20, 17 inches, 92 minutes

The higher the bulb is above the screen, the longer it needs to be exposed. If the wattage of the bulb is lower, you need to exposure it longer.

Here’s a great way to test which time will work best for you. 

Print a transparency with numbers from 10 to 90 in increments of 5. With the light set up, place the screen under the light to be exposed. After 10 minutes, cover the 5 with an opaque piece of paper. After another 10 minutes passes, cover the 10.Do this until all of the numbers are covered. Then wash out the screen. The lowest numbers that are distinctly printed will give you your correct exposure time.

(This method also works for exposing with the sun but as the seasons change so will the UV intensity of the sun so you may have to do this often.)

Happy Printing!