Learn how to do a basic underbase separation in Photoshop for screen printing. There are a couple techniques we use to create an underbase. In this tutorial we duplicated the spot color channel seps and choked each channel before adding the channel to the underbase channel. Using this technique of creating an underbase allows us to control the amount of ink in the underbase. By adding more or less you can control the amount of ink you'll deposit on the shirt while on press. If you use a 50% underbase you can make the overall print softer then using a solid underbase. You can also change the top spot color as well. So those are a couple variable to keep in mind. We suggest using a RIP software to output your film positives to control the LPI and ink density.