| Exposing a screen printing screen is like exposing a | | | | able reproduce the results in the future. |
| photograph. For the best results, you need to | | | | Now you are ready to run a test to find the best |
| expose it for the optimum amount of time. If you | | | | exposure time. Here are some base times to start |
| expose it a little less, or a little more, you will still | | | | with (based on a 150 clear incandescent bulb): |
| probably be okay. But the farther you get away | | | | 12 inches above the screen, 45 minutes |
| from the optimum time, the more your results will | | | | 15 inches above the screen, 74 minutes |
| suffer. The variables for figuring out the correct time | | | | 17 inches above the screen, 92 minutes |
| are brightness of the light source, and distance from | | | | The higher the bulb is above the screen, the longer |
| the screen. | | | | the exposure needs to be. If the wattage of the |
| You need to decide on a light source. I currently use | | | | bulb is lower, you need to lengthen the exposure |
| a 250 watt halogen work light with the UV filter | | | | time. If the wattage is higher, then you need to |
| glass, and safety cage removed (you assume all risks | | | | shorten the exposure time. If you use a different |
| if you remove your glass and/or cage from your | | | | kind of bulb, the time may vary. |
| halogen light). In the past, I have used a 75 watt | | | | Here is how to test for the best exposure time: |
| incandescent bulb in a reflector with a clamp. | | | | Coat a screen with photo emulsion the usual way. |
| Whatever you use, make sure you have some way | | | | Print a transparency with numbers from 10 to 90 in |
| of clamping it, or mounting it above the frame for an | | | | increments of 5. If you are using a low wattage bulb, |
| extended period of time. | | | | you should use higher numbers in increments of 10. |
| You need to place the light far enough away from | | | | With the light set up, place the coated screen under |
| the screen, so that the whole screen is being equally | | | | the light to be exposed. Use a clock or stop watch |
| lighted. If the center of the screen is significantly | | | | to keep track of the time. After 5 minutes, cover |
| brighter then the corners, than the light is too close. | | | | the 5 with an opaque piece of paper or cardboard. |
| The bigger the screen, the farther you are likely to | | | | After 10 minutes, cover the 10. Do this until all of the |
| have to place the light source. The farther away the | | | | numbers are covered. Then wash out the screen. |
| light source is, the longer the exposure time will be. | | | | The lowest numbers that are distinct on the screen |
| Measure the distances, and record it, so you will be | | | | will give you the optimum exposure time. |