Technical

CMYK simulated process printing on custom T-shirts and clothing

Michel Leblanc | 13 July 2009

Simulated process t-shirt La MauditeLa Maudite simulated process T-shirt

T-shirt Unibroue

Do you understand what we mean with that complicated title? In screen-printing jargon, “simulated process” is used to refer to a high-quality printing process.

When used well, simulated process can reproduce any image over any background colour. This technique is an art, and those with the talent and patience to develop it have access to a wide range of technical and creative possibilities. Part of W2’s reputation has been built on the extremely high quality of its reproductions on clothing, particularly using simulated process printing.

On paper, to reproduce a multi-tone image using offset printing, such as a photo or illustration, you use 4-colour process reproduction. By separating out the colours and printing them with Cyan, Magenta, Yellow and Black (CMYK), you can reproduce almost anything. The process is so common that it’s become mundane; even digital printers use this process.

But textile screen printing is much trickier. To begin with, there are many limitations and constraints: significant dot gain, low resolution (50 to 65 lpi in general), shininess, “muddy” tertiary colours, etc. And that’s not even when you’re printing on a coloured shirt!

When printing on coloured fabric, you must first print a white underbase, work with opaque colours, and flash-cure certain colours. Often, the results are underwhelming: we’ve all seen one of those shirts with a horrible disk of plastic ink on it.

A key element to making a nice reproduction lies in the quantity of underbase you use: to make sure the fabric stays soft, you have to limit the underbase to areas of the image where the colours are bright or where the image is white. To make things trickier, the underbase also depends on the colour of the fabric. For example, red printed on orange fabric doesn’t need an underbase. The same goes for dark red on black fabric: print a pure red directly on black fabric, and the result will be dark red. A second white is often also used, printed at the end, to enhance the details and highlights in the image.

The inks all have different levels of opacity, which makes the task of separating them much more involved. But this constraint can work to our advantage; by printing directly on the fabric, without white sections underneath, we can get some nice nuanced dark colours.

Colour selection must be very precise. If there is green in the image, we have to print green, not overlapping yellow and cyan. This requires a broader range of colours for reproduction; 6 colours is standard, but we often use up to 8 colours. Of course, the fabric is also a “colour,” which complements the range of colours we use. On a black T-shirt, the black in the image is the black in the T-shirt.

In the end, the term “simulated process” is a bit nonsensical, because a process is already a simulation. That leaves us with a simulation of a simulation! A term like “extended process” would be a little more accurate: more colours, an interaction with the background and very precise colours.

At W2, we’ve developed our own techniques for colour separation. Every image is processed on a case-by-case basis. This job goes beyond the computer screen—you have to get behind the screen-printing press where many adjustments often have to be made.

Claude de Repentigny
W2 Co-Associate

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