Screen Printing Underbase Basics

by Gary Jurman October 16, 2009

This video demonstrates the basic idea of underbasing. When you see a bright colored ink on a dark fabric, chances are it has been underbased. While the video focuses on an underbase using Plastisol ink, waterbased inks are often underbased as well. Some topics briefly touched on are Traps, Spreads, Chokes, and Flash Drying (aka. flash curing).

Special Note: You may notice that the particular underbase demonstrated in the video requires tight registration (alignment of the screens) because of the level of detail in the lines and knockout lettering. This level of registration is very difficult to achieve and maintain on non-professional screen print presses like the Yudu Personal Screen Printing Machine or the ones found in hobby kits. The Merchmakr can do it, though!

Transcript of the Video

"Ok, so what we want to talk about today is underbasing. What we want to do with an underbase is we're going to put a layer of white ink underneath the print so that it can appear brighter."

"This is what the customer sent in. It is a graphic with some "knockout" text that's really tiny and thin, and some thin lines like in the trigger guards of the guns in the logo."

"What we want to do is produce this on a black garment. This is kind of a "tuffy" because to get all that detail in, you need to put it on a higher resolution screen."

[Special Note: higher resolution screens don't allow as much ink to pass through them, resulting in a thinner layer of ink on your garment, and as a result, a less opaque image.]

What I chose to do is put the YELLOW on a 230 Mesh so that we can get the nice, little, thin lines in the detail. ...but then, here-in lies the problem: when you use such a high resolution mesh with a low-opacity ink (or an ink that doesn't mask what you put it on), you don't get a real bright color on your garment.

"What I'm going to do is demonstrate the problem and show you a solution."

  • "We want to print this on a black garment."
  • "This is a 230 Mesh Screen"
  • "We're going to print with YELLOW INK This is a high opacity yellow ink, but it's still not opaque enough."

"I'm going to lay down our first layer of ink, and we can take a look at what the effect is."

"What we have here is we put down our first print and you can see that some of these lines look OK, and it's still readable in the text, but on the other end of the spectrum you have a really poor coverage. You can see the black of the shirt just pushing right through the ink. You can see that the ink is not very opaque: it's not masking the color of the shirt very well."

"Okay, so I've got a flash unit set up over here, and we're going to rotate this under the flash unit and dry that color."

[Prints a second layer of ink over the flash-dried first layer]

"That looks a whole lot more opaque --it looks a lot better, but your letters are starting to close up a little but, and after a couple of prints they're going to be completely filled in even though I'm using a nice, sharp squeegee on this."

"One other issue is that when I run this down the dryer the ink will become slightly less opaque, and you'll see that modeling coming through a little bit more again."

The Underbase Solution We Decided On.

"So what we decided to do instead of running it this way and having to constantly have to manage these tiny lines in the 'crime scene do not cross,' is to use a white ink underbase to make it nice and bright, but also to leave a nice contrast on the interior of the lettering."

"To create the underbase we made a second film that is a lot like the first film, but the big difference is that we did a trap. What we did was to choke the underbase." [see sidebar for definitions.] "We made it smaller than the print that goes on top. The reason to do that is when you print the underbase it's going to spread and poke out from the edges [of the topcoat] and you really don't want that."

"So we made the underbase and we put it on this screen, and here's what the underbase looks like."

[Prints WHITE Underbase Screen]

"Note on this underbase: you can see that there is a difference from the top-coating where we choked inside the lettering. You see how the lettering right here is a whole lot more open --more open than we really want it, but it's going to fill in when we overprint it. Also look how the trigger guards in the weapons is even incomplete. That's okay, it'll all pan out when we flash-dry this and print the second layer on. You'll see how bright it becomes."

"Also take a look at this line, here, you can see that it's much thinner than the final line will be printed. It's all going to pop once we flash-dry it and put the second coat over it."

"Now this WHITE is only a one-hit WHITE so it might not look super opaque to you but once we lay the YELLOW over it's really going to pop. And note when I do drop the screen and print, how the text is going to change in here, how the trigger guards will appear in the YELLOW, and how this line is really going to pump out."

"So we're back to the same YELLOW we printed before."


[Starting with the YELLOW flash YELLOW]

"So you can still see a little bit of the modeling in the one with the YELLOW underbase. This part right here has the WHITE underbase. You're going to really see this, especially if you're printing on 50/50 garments, where this part here is going to dull down a lot. This part here is going to appear much brighter than it would over here."

Basic Vocabulary:

  • Flash dry: To dry a layer of ink without fully curing it in order to allow a second layer of ink to be printed on top of it.
  • Knockout: When an image is created using negative space or unprinted ink. As an example, a knockout "K" is created when a large square of ink is printed except for the area where the "K" is.
  • Trap: When two layers of ink (often different colors) overlap each other. The purpose of a trap is often to either hide mis-registration of art or to decrease setup time on the press because registration can be less precise when a trap is used.
  • Choke: A type of trap used where the edge of an underlying object is receded so that an overlapping object can have a wider trap.
  • Spread: A type of trap where an overlapping object has an edge extended in order to create a wider/fatter trap with the underlying object.
Gary Jurman
Gary Jurman

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