Get an image ready for screen printing

A screen prints one ink at a time. Every colour in the design is a screen of its own, burned through a film positive that carries that colour's shapes in solid black (Anatol).

Flat colours. Spot colour separation, one film per ink, is done from vector artwork. Ryonet notes that "most screen print designs are one to three flat colors or a spot color" (Ryonet), and every colour is a screen to coat, expose and line up.

No shading, unless it's halftones. A gradient or a shadow can't print as one flat ink. It needs halftones, dots of ink that read as tone. Tracer doesn't make halftones: it turns soft tones into flat bands, which can work as a poster look but isn't the same thing.

Detail the screen can hold. One shop's guidelines ask for "lines no thinner than 1 pt" and text no smaller than 8pt (Oregon Screen). A trace keeps every hairline in the image, so check the artwork at print size.

Print size. Anatol's advice is that "even vector images should be prepared at or near the actual print size" (Anatol). Tracer's EPS has one point per pixel of the traced image, so a 1,000-pixel image comes out about 35cm wide, and its SVG has no physical size at all. Scale it to the print before you separate.

Print shops ask for vectors; Oregon Screen's list is "Vector Files – .ai .pdf .eps .svg". Tracer exports SVG and, on Pro, EPS and PDF. It doesn't write AI files.

The outline on colour shapes. In a colour trace's SVG and PDF, every shape carries a thin stroke in its own colour, which closes hairline gaps on screen. It makes each shape half an image pixel bigger all round, a small spread already built in. The EPS has the fills only.

The colours are RGB, not inks. Tracer writes each layer's colour as RGB. Which ink, Pantone or otherwise, prints each layer is decided in separation.

Tracer's colour styles split the image into four bands of brightness and fill each band with the image's own colour for it. Each layer is then a candidate film. Colours of similar brightness land in the same band, though: a red and a blue of about the same lightness come back as one colour, on one layer. Check the layers against your design first, then:

• —It is always four layers. A design in two or three colours comes back with near copies among the four, and each one would be another screen. As Screen Printing magazine puts it, "if you print fewer colors and achieve the same result, you will make more money" (source). Delete or merge them.
• —The layers are stacked. The lightest layer covers the whole design, and each darker one sits on top of it. Output as they are, every film also carries the areas of the colours above it, and the inks print over one another. For knockouts, take each upper shape out of the one below it.
• —Then trap. Colours that only touch show a gap when a screen shifts. The basic methods are overprint, choke and spread, and they exist "to compensate for any possible misregistration" (Graphics Pro).
• —The background is a layer too. A white or coloured background traced as a shape becomes a screen of its own. On a one-colour trace, turn on Remove background before downloading; on a colour trace, delete that layer in your editor.

• —Films in solid black. "Change the color on each layer to pure black for printing the positive" (Anatol). A film that's too light "won't expose correctly and you'll lose valuable detail" (Ryonet).
• —Registration marks. "Add registration and center crop lines to each image layer", so the films, and then the screens, line up (Anatol, same guide).
• —Underbase on dark garments. On a dark shirt, a white or light grey underbase prints first and is flash cured before the colours go on top (Anatol).
• —Coat, dry, expose, wash out. Coat the screen with emulsion, let it dry in the dark, expose it through the film, and wash it out (Anatol).

• —Starting from a web image. "Web-based art is 72 dpi at the actual screen size, and was never intended to be screen printed" (Screen Printing magazine). Trace from the largest original you can get.
• —More screens than the design needs. Four near-identical layers are four screens. Merge them first.
• —Tracing a photo for a flat print. The tones turn into flat bands. A photographic print needs halftones, made from the original image.
• —Lines thinner than the screen holds. Lines under 1pt "will likely be too thin to print" (FM Expressions). Thicken them or leave them out.
• —No trap. Colours that butt against each other show slivers of shirt when a screen moves.
• —A white box on the film. That's the traced background. Remove it before you separate.