Gradients and Halftones in Screen Printing

There’s some good conversation on Blake’s post about how to take your t-shirt artwork from good to great.

Jake asked: “What is the best way to blend colors using half-tone patterns that will translate well to screen-printing? Any common mistakes or things designers should be aware of?”

Well Jake, here’s the (really long) answer to that.

Let’s start with a brief explanation of what exactly halftones are:

Basically, halftones are regular patterns of tiny shapes (dots, ellipses, squares are common) that taper out to create the appearance of a color fading (or graduating) to white or another color at the edges.

Take a gradient (like the above left) and render it as a halftone pattern, zoom in a bunch, and it would look something like the above right.

When a screen printer outputs a graphic that contains gradients onto films (which are used to burn screens – which is what the ink goes in), what they’re really outputting are these halftones. If you look closely at a screen printed tee that has gradients, you can actually make out these patterns:

But seen from a distance, it makes a perfect blend. You can see it best on shirts that only have a few colors and are especially ones printed on white:

Printers can adjust the angle, frequency and shape of these dots to increase or decrease the dot size of the halftones. Larger dots = more space in between them, more visible gradient appearance; Smaller dots = less space between them, tighter, smoother gradient appearance.

A lot of this is technical stuff that you never need to worry about as a designer (your screen printing will do all the work with setting up the correct halftones to make your gradients print well) but you can make their life easier by prepping your artwork correctly and understanding a little bit about the process.

Here’s some things you should know about printing gradients:

• Understand Mesh Size
  The screens used for printing come in different mesh sizes ranging anywhere from 40 to 230. The lower the mesh size, the larger the holes in the screen and the more ink is pushed through to the shirt.

  Gradients require the opposite end of the spectrum: high meshes that don’t let a lot of ink through (otherwise the little dots all blur together and look like a blob). Not all screen printers have these higher mesh screens required to do gradients, which is why many of them don’t.

• Be aware of the trade-offs of mixing large solid areas and gradients in the same color
  If you have a color in your design that covers a large of area and has gradients, the printer is suddenly faced a dilemma. Do they chose the high mesh screen that will print the gradient without blurring (but lay down less ink in the places the color has large coverage)? Or do they chose a lower mesh that will give good coverage to the large areas but potentially blur the halftones.

  Generally, there’s a decent in-between option, but most printers will opt to preserve the halftones. So you may notice some lighter/sketchy coverage on the large solids.

• Halftones and Underbases don’t mix well
  An underbase is used when printing on dark shirts to provide, you guessed it, a base for the design to keep the colors from getting absorbed into the fibers of the shirt, and preserve vibrancy. It’s usually a white or light gray, and underlays the entire design (or most of it, depending on the color of the shirt and colors of ink being used). Because you’re covering such a wide area with ink, underbases are generally on a lower mesh screen, which almost never agrees well with gradients… which brings me to our next item:
• Sometimes your solids and gradients can (and should) be printed separately This generally adds to the cost of printing your design (because most printers charge per screen), but it can be a good solution if you have issues with coverage, or a design that’s going to have a white underbase and gradients that fade from color to the shirt.The solids are outputted on one screen with a lower mesh, and the gradients are printed with the required higher mesh.

And here’s some things you should do with your artwork to make outputting your gradients easier:

• If you’re working in a vector program, make sure all your colors (including gradients) are in PANTONE colors.
  This includes using a PANTONE white for gradients that go from a color to white. When prepping your artwork, the printer needs to convert all RGB/CYMK colors to PANTONE for output, and they’ll hate you less if they don’t need to go through and replace colors in the 200 objects of your design that have gradients.
• Don’t flatten your image if you’re designing in Photoshop or another bitmap editor
  This is good advice for any design regardless of whether it includes gradients or not, but it’s significantly easier to split apart the colors of a gradient when they haven’t been combined together.
• And finally… don’t try and use gradients on highly detailed, small areas of your design
  Remember the dots from the up close picture of a halftone? These dots can only go so small, and in smaller areas of your design it can be hard to concentrate enough of them to visually see any time of transition.