· 4 min read · By the DesignFix team
A screen printing press can't print a picture. It can only push one ink through one screen at a time. So before anything is printed, the artwork has to be taken apart into layers, one for each ink, and each layer becomes its own screen. Those layers are the color separations.
Separations decide how many screens a job needs, what it costs, and how the finished shirt looks. If you order screen printing, or you're a shop explaining a quote to a customer, it helps to know what's happening at this step.
What a separation actually is
Take a logo with red, blue and white on a black shirt. The separator produces a black-and-white image for each ink: one showing only where the red goes, one for the blue, one for the white, and usually one more for the white underbase beneath everything.
Each image is printed onto clear film or sent to a direct-to-screen system and used to make a stencil on a mesh screen. On press, the screens print in order and the layers stack up into the full design.
Four inks, four screens, four setups. That's why color count is the first thing a screen printer asks about.
The three main types of separation
Spot color
Each color in the design is a separate, solid ink, mixed to a specific shade, often a Pantone match. This is the standard for logos, text, team wear and most business orders.
- Looks: bold, flat, very vivid
- Best for: designs with one to six distinct colors
- Needs: clean artwork with clearly defined color areas, ideally vector
Shading is still possible in spot color work using halftones, where a solid ink is broken into tiny dots to look lighter. One blue ink can print as solid blue and as a pale blue tint.
Simulated process
Used for photos, paintings and highly detailed illustrations, especially on dark shirts. The image is separated into a set of spot inks, often six to ten, printed as overlapping halftones that blend into a full-color image.
- Looks: photographic, with strong color on dark garments
- Best for: complex art where spot color would need too many inks
- Needs: a high resolution image and an experienced separator. This is skilled work.
Four-color process (CMYK)
The image is split into cyan, magenta, yellow and black halftones, the same idea as a magazine print. It works on white or very light shirts and uses only four screens, but the colors are less vivid than simulated process and it's hard to keep consistent on fabric.
- Looks: full color, softer and less saturated
- Best for: photographic prints on white shirts
There's also index separation, which builds the image from square dots of a fixed set of colors. It's less common but very stable on press.
Why color count drives the price
Every screen has to be coated, exposed, washed out, taped, registered on the press and cleaned afterward. Shops charge a setup fee per screen, and more colors mean a slower run.
On a small order, that matters a lot. Dropping a design from six colors to three can cut the price per shirt noticeably on a run of 48. On a run of 1,000, the setup cost is spread so thin that color count matters much less.
This is why printers suggest simplifying art for short runs. It isn't laziness. It's the math of the method.
The underbase and the order of printing
On dark garments, a white underbase goes down first so the colors on top stay bright. It's usually choked, made slightly smaller than the colors above, so no white shows at the edges. Many shops flash-cure it and add a second white for the brightest highlights.
Where two colors meet, separators use trapping: one color is spread slightly under its neighbor, so a tiny shift on press doesn't open a gap. Good separations build this in. Poor ones leave thin slivers of shirt showing between colors.
What artwork separates cleanly
Separation is fast and accurate when the file is prepared for it:
- Vector artwork with each color as a distinct, named swatch
- A limited palette with no near-duplicate shades
- Text converted to outlines
- Lines and gaps thick enough to hold on a screen, about 1 pt or more
- Pantone references for any color that must match
- For photographic work: a 300 PPI image at print size, not a compressed JPG
And it's slow, expensive or impossible when the file is the opposite:
- a small JPG with fuzzy edges, where the border of every shape is a blend of several colors
- an auto-traced vector with hundreds of tiny shapes and a dozen reds that should be one
- gradients and shadows built with effects the separator has to rebuild
- a flattened image with the background still attached
A separator can't separate colors that aren't cleanly separate in the file. Someone has to rebuild them first.
How to make your printer's job, and your bill, smaller
- Send vector art whenever the design is a logo or graphic
- Decide the number of colors before you ask for a quote
- Say what shirt color it's going on
- Give Pantone numbers for brand colors
- Ask whether shading will be done with halftones, and approve a proof
- For photos, ask whether simulated process is worth it at your quantity
The short version
Color separation turns one design into one screen per ink. Spot color is for clean graphics, simulated process for full-color art on dark shirts, and CMYK for photos on white. More colors mean more screens and more cost, and clean, vector artwork is what makes separations quick and accurate.
If your artwork isn't ready to separate, with fuzzy edges, too many shades or no vector version, we can rebuild it with clean, flat colors. See our vector tracing service, or our page on color separation.
- screen printing
- color separation
- vector files