Screen printing has become the modern go-to printing technique. But when your beautiful design includes gradients, preparing your artwork for print quickly becomes an unexpected nightmare. Don’t worry, we’re here to help.
What you’ll need:
- The Illustrator File (CS4)
- Adobe Illustrator
- Adobe Photoshop
A Brief Definition of Screen Printing
Screen printing is a printing technique in which ink is pushed through a fine mesh screen, which has a stencil of your design.
- First, you coat the screen with a light-sensitive emulsion.
- Then, you place your photo negative image on top of the emulsified screen. Your image is printed in pure black on a transparent surface, such as a piece of transparency paper, or vellum.
- Expose the screen to a strong light source, ensuring that your image is between the light and the emulsion. The emulsion covered by your image remains unexposed, while the exposed emulsion dries.
- Remove your image, and rinse out the screen. Like magic, the previously protected emulsion washes away, leaving a stencil.
- Push your ink through the screen…
- And now you have your print!
Screen printing is a one-color process meaning you print every color separately using a separate screen. For example, if you want to print an image with dark red & pink, you would print the dark red first (1), then print the pink (2) on top of that to create a final image (1+2):
The Problem with Gradients
Gradients present an issue in Screen printing because of the screen burning process.
With digital printing, every color is printed simultaneously & precisely with varying percentages of Cyan, Magenta, Yellow and Black. When you use a digital printer, your gradient is perfectly fine as rendered on the computer because digital printers can print gradients by merely fading out the amount of ink used:
But when preparing your file for screen printing, it is essential to use halftones because you need a pure, solid color to block the light and burn your screen correctly.
Screens also vary by mesh: a higher mesh means a screen is more tightly woven, which allows for more detail but also allows less ink to pass through; a lower mesh is the opposite, more loosely woven allowing more ink to pass through to better print large areas of color. So you can create finer, smoother gradients by using a higher mesh screen.
Halftones are the answer
Changing your gradients into halftones allows you to create the visual appearance of a smooth blend but still block light properly. When done right, halftones are only visible at very close distances:
How to Separate Gradients Using Halftones
Before starting the tutorial, here are a few important factors to keep in mind about your future designs:
- Just like other situations, if your original file is raster, create it at actual size.
- How fine of a mesh will your screen printer be using? If your artwork is very detailed, this is a good thing to specify.
- How many colors will you use? A ten-color design might look great, but often times clients will want a more affordable option – screen printers will charge more to print additional colors.
- And of course, is your design best-suited for screen printing? Sometimes a certain design, like a photograph, just doesn’t work as a screen print. It’s okay, accept it and move on.
This tutorial is geared towards beginner to intermediate screen printers/designers and people looking for a fairly simple, straight forward process without the need of additional programs or software. In this tutorial we will be preparing a vector rose graphic for a 3-color screen print. Let’s begin.
Create Spot Colors
We will first change each color into a ‘spot’ color, so that it is no longer a CMYK mix, or Process color. This makes it easier to separate each color into it’s own layer to burn separate screens.
1. Open the ‘halftone-gradient-tutorial.ai’ file (Download above)
2. With the Selection Tool, select the rose fill, the blue to red gradient.
3. Open up your Gradient window (Window > Gradient) and select the left, cyan color stop.
4. With the color stop highlighted, go to your Color window. Click and drag the cyan box into your Swatches window to create a new cyan swatch.
5. Now select the right magenta color stop in your Gradient window.
6. Your color window should now have a magenta box. As before, click and drag the box into your Swatches window to create a new magenta swatch.
7. Deselect the rose.
8. Double click your newly created cyan swatch.
9. In the dialogue box, change Color Type from ‘Process Color’ to ‘Spot Color’ and click ‘OK’.
10. Turn the magenta swatch into a Spot Color, using the same method.
11. Reselect the rose.
12. Click and drag the cyan spot color onto the left gradient swatch. Also replace the right color stop with the magenta spot color.
13. Your rose gradient is now using both spot colors.
14. Save your progress.
Separate Your Colors
We will now separate each color to print individually. Although each color will save as black, remember that a black ink image will block light the best for screen printing. You choose the actual ink color for your image once you’re finally printing through the burned screen.
1. Go to File > Print…
2. For ‘Printer:’ choose ‘Adobe PostScript File’ and leave ‘PPD:’ as is.
3. Select ‘Output’ from the options on the left.
4. For ‘Mode’ choose ‘Separations (Host-Based)’ (This could vary depending on your printer)
5. You can leave Emulsion, Image and Printer Resolution to their default settings.
6. In the Document Ink Options, turn off every ink other than the cyan spot color, by clicking the printer icons next to each ink. See screenshot below:
7. Click ‘Save’ – Name the file ‘Cyan Spot Channel’ and click ‘Save’
8. Repeat this process to save a file for the Magenta Spot Channel, and lastly for Process Black – you should end up with 3 separate saved files.
Note: For future projects, be sure your artboard is the same size as your art, otherwise your Adobe PostScript File will be cropped.
Create the Halftones
We’re almost done, but we need to finish the process in Photoshop.
1. While still in Illustrator, go to File > Open to open one of your newly created PostScript files – I will use ‘Cyan Spot Channel’ as the example. On Mac, you must first specify Adobe PostScript files to open in Illustrator.
2. Select the black to white gradient with the Selection Tool.
3. Copy your selection.
4. Open Photoshop and create a new document. The settings should match that of your copied gradient, but just in case, the dimensions should be 2289px wide, 2269px tall, 300 ppi.
5. For ‘Color Mode’ choose Grayscale.
6. Paste the object into your Photoshop document – Paste As: Pixels – Click ‘OK’ – Hit Enter to commit to transform.
7. Hit Control + L, or Command + L on Mac, to bring up the Levels dialogue box.
8. Move the left black color stop to the beginning of the graph, around ’23′. Click ‘OK’.
9. Go to Image > Mode > Bitmap…
10. ‘Flatten Layers?’ click ‘OK’
11. Output: 300 ppi and for Method choose ‘Halftone Screen’. Click ‘OK’
12. You can leave Frequency and Angle at their defaults, but change Shape to ‘Round’ – Click ‘OK’. Note: Changing certain Bitmap settings will help you achieve your desired result, based on the amount of detail you require.
13. Go to File > Save As and save as whatever file type your printer needs – PDF’s are the most widely accepted format.
14. Simply repeat this last set of steps for both your other colors (in this case, Magenta and Black), and your files are ready to go! Note: You should make each file a different Angle for best results.
A zoomed in shot of the final screen-ready image. When zoomed in extremely close, the image will appear pixelated, but at actual print size, it works great. Again, you can also toy around with the Bitmap settings to achieve your ideal results.
If you have any comments, questions, or feedback, we would love to hear from you. Also feel free to share any tips or other strategies as to how to go about the gradient halftone separation process. Thanks for reading.