To make screen printing separations in Illustrator, convert every color in your vector artwork to a named spot color swatch, set overprints and traps where colors meet, add an underbase for dark garments and registration marks, check the result in the Separations Preview panel, then print each spot color as its own film. Because the art is vector, edges stay sharp at any size.
Below is the full spot color workflow, step by step, with the panel and menu names you will need.
Why Illustrator suits spot color separations
Most spot color artwork, such as logos, type, badges and flat illustration, is vector, and in Illustrator each swatch can stand for one ink. Once every object uses a spot swatch, the separation is already mostly done: Illustrator knows which shapes belong to which ink and can output one film per swatch.
Compared with separating in Photoshop, there is no selecting by color range and no cleaning up soft edges. The trade-off is tone. Illustrator is weaker at photographic shading, so tonal art is usually better separated in Photoshop, as covered in our guide to color separations in Photoshop.
Step 1: Set up the document for film
- Match the artboard to your film. ScreenPrinting.com's tutorial recommends making the artboard the size of the film you will print, so you only design and separate what will actually be output.
- Use a print workspace. The same tutorial uses Illustrator's preset Printing and Proofing workspace, which puts the Separations Preview, Attributes and Swatches panels within reach.
- Size the art to the print. Scale the design to the exact width it will print on the garment before you add traps, because trap sizes are physical distances.
- Know your ink count. Decide the shirt color and the inks before you start. Every ink is a screen.
Step 2: Convert every color to a spot swatch
- Click an object in the first color, then choose Select > Same > Fill Color to grab every object in that color.
- In the Swatches panel, click New Swatch, set Color Type to Spot Color and give it a clear name, such as the ink name or its print order.
- Apply the swatch to the selection and repeat for each color.
Watch for near-duplicates. Two reds that differ by a few percent will become two screens unless you merge them into one swatch. This is the cheapest moment in the whole job to cut a screen.
Name swatches by what the printer needs. "White base", "Red 02" or an ink code from your supplier are all clearer than "Spot Color 4".
Step 3: Decide what knocks out and what overprints
By default, a shape on top knocks out the colors underneath it, leaving a hole the exact shape of the top object. That is right for most spot work, because inks on fabric print best on bare shirt or on the underbase, not stacked on each other.
Sometimes you want a color to print over another instead. Thin black outlines and small dark text are the classic case: letting them overprint means there is no hole underneath to register against. Select the object, open Window > Attributes and tick Overprint Fill (or Overprint Stroke for strokes).
Overprint is invisible in normal view. Turn on Overprint Preview in the Separations Preview panel to see what will really print.
Step 4: Trap where colors meet
Screens never register perfectly. If two colors simply butt together, any drift on press leaves a thin line of shirt showing between them. Trapping makes neighboring colors overlap slightly so that gap never appears. Our guide to trapping, choke and spread explains the theory; here is how it works in Illustrator.
- Spread with Offset Path: select the shapes of one color and use Object > Path > Offset Path with a small positive value to grow them under their neighbor. A Smashing Magazine walkthrough uses around 1 mm for fabric work; tighten it on an automatic press that holds registration well.
- Stroke and overprint: add a stroke in the same spot color to the lighter object and set that stroke to overprint, so it spreads into the darker color.
- The Trap option: Illustrator also has a Trap command in the Pathfinder panel and as an effect. Prepress users note it only traps simple solid objects and flat tints, not gradients or images.
| Technique | What it does | Use it for |
|---|---|---|
| Knockout | Removes the color underneath the top shape | Most spot colors on fabric |
| Overprint | Prints the top color over the one below | Thin black outlines, small dark text |
| Spread | Grows a color outward under its neighbor | Lighter colors meeting darker ones |
| Choke | Shrinks a color inward | Underbases, so white never peeks out |
Step 5: Build an underbase for dark garments
On a dark shirt, colors need a white layer printed first. Create a spot swatch called something like "White base", copy every shape that needs brightness, merge them into one shape with the Pathfinder Unite button, and fill it with that swatch on its own layer at the bottom.
Then choke it. Use Offset Path with a small negative value so the underbase sits just inside the colors above it. If it is the same size, any misregistration shows a white edge.
For proofing, the Smashing Magazine walkthrough suggests a temporary background rectangle in the garment color on its own layer. It makes the colors look the way they will on the shirt. Delete or hide it before output, or it will print as a screen.
Step 6: Add registration marks and check the separations
Place matching registration targets outside the art and fill them with Illustrator's built-in Registration swatch, which prints on every separation plate. ScreenPrinting.com's 5-step Illustrator separation guide uses one mark at the top and one at the bottom for small prints, and three across the top and bottom for standard-size designs.
Now open Window > Separations Preview. Turn off the cyan, magenta, yellow and black plates. If anything disappears, it is still a process color and would create an extra film. Fix it, then click through each spot color on its own to confirm every shape is where it should be.
Step 7: Print the films
Each spot color prints as its own film positive: solid black where the ink goes, clear everywhere else.
- Through Illustrator's print dialog: choose File > Print, select a PostScript output, and in the Output section set Mode to Separations (Host-Based). Only your spot inks should be listed as plates. Set emulsion and positive or negative to match your film and exposure setup.
- Through a RIP: most screen shops print films through RIP software such as AccuRIP, which prints directly from Adobe apps to supported inkjet printers and gives denser, more consistent blacks than a standard driver.
Label each film with its ink and print order, and overlay them on a light table against a composite proof before anyone coats a screen.
When the artwork is not vector
Plenty of jobs arrive as JPGs, PNGs or flattened PSDs. You can trace them into vector first, separate them in Photoshop, or use an automatic spot color separator.
Texloom's Separation Studio takes a raster image or PSD and splits it into spot color plates automatically, or into exactly the number of screens you set, from 2 to 12. It adds 0 to 4 px of trapping, registration marks on every plate and an optional white underbase, names each plate after its nearest color in the Texloom Color Library, and exports a ZIP of PNG plates, a multi-page TIFF or a layered PSD. For the bigger picture on methods and halftones, see our color separation guide.
Next step: open your last logo job in Illustrator, run Select > Same > Fill Color on each color and count the swatches. If the count is higher than the inks you meant to print, merge before you go any further.
