Multi-colour Digital Mockup for Screen Printing

[WORKING FILE]

Trying to digitally mimic the often serendipitous, and predominant guesswork of transparent screen printed layers of ink on paper is very difficult. One of the biggest obstacles we face is that most inks we use for screen printing have some unquantifiable level of transparency to them. This guide was created to help understand how digital colour separations work in relation to the real life building of ink layers on paper.

Here is a 3 colour image, mocked up digitally. To the right are the 3 colours used and below are the output equivalents:

PIGMENT, BASE, COLOUR

Generally, pigments rely on the whiteness of the paper for their brightness. So a highly saturated colour is mostly pigment, we then add a transparent base to brighten the colour.

Colours are mixed by eye, so the print technicians’ skill and experience is one factor into how the digital image is rendered on paper.

[ insert image: 3 swatches = 100% cyan / 50-50% cyan and base / 10% cyan and base ]

The way the ink is composed is determined by the outcome in relation to the other inks. So a dark red can be made by using just 2 colours, Medium Red + Black. But if that colour is to be used as an overlay, the technician would take that into account.

[ insert image: 2 similar reds on blue, one transparent, one as opaque as possible ]

 

DIGITAL COLOUR LAYERS

Image manipulation programs like Pixelmator, Gimp, and Photoshop have layer effects like ‘multiply’ and ‘darken’,
but I don’t think they really help us understand in the digital world how things will look in real life.

I usually avoid those layer effects and work directly with the layers’ opacity level when trying to mimic transparent colours. A good % range to work with is 50-70%. I’ll start with 55% in the example below:

 

Once the layers’ opacity is dropped, I ignore the pantone colour and visually alter the hue, saturation, and lightness of the colour to my liking. This is similar to the print technician adding white,black, or transparent base to colour match.

You will find that visually, your colour saturation level will be capped by the % of transparency that you gave your layer.
This holds true to real life where more transparent base will eventually yield a less intense colour.

At this point I need to change my layer transparency level to visually match what I want to see. I changed the 255u Magenta layer from 55% to 70% to give it more punch.

Because I am now referencing colours visually instead of with a physical pantone book, I change the the pantone colour names in the Layers window so as not to confuse anyone.

Also, we generally screen print layers from lightest to darkest. Note above right; I changed the layer order of the magenta and blue layers. I want the colour block in the middle of my image to be more magenta than blue. So I reorder the layers so the magenta is printed last.

 

PANTONE VS ‘MATCH TO SCREEN’

When I don’t have a pantone book on hand, I generally just ‘match to screen’. I change the name of the layer from a pantone colour to a descriptive word for colour reference. This is done so that I am not confusing the technician who is mixing the colours.

IT IS VERY IMPORTANT if you DO NOT have a Pantone book, DO NOT reference Pantone colours in your digital file. Most of the time, a pantone colour chosen in a digital program will not look like the real life swatch in our hand.

Digital files from any of the apps mentioned above carry an imbedded colour profile which helps make colours look visually similar across different monitors (when opened in their respective environment). While this may not always be perfect, especially when going from a Windows machine to our Mac, it is still better than guessing a Pantone match.

THE FINAL MOCKUP

I finish my digital work with 2 files:

  1. The 300 dpi, 100% to size, layered file (marked ‘out’ or ‘final’).
  2. The 72 dpi mockup file.

In order to go from digital to screen print, the colour layers need to be converted to grayscale. Then the grays need to be turned into halftones or dissolves to make every layer contain either black or white pixels. Black is where the ink colour sits, and white is left as paper.

 

The above screen capture shows a ‘print ready’ file. It is a layered file in grayscale. The file is 12″x18″ (100% to size) with a resolution of 300 dpi. The area that looks gray is actually black and white halftone dots at 50 lpi.

Grayscale-to-Bitmap

This is the gray layer, converted to disolves and halftones. The black area will be replaced with a Gray 4u ink when printed.

The ‘Threshold’ filter is helpful as well to determine what your layer will look like on a screen mesh. Threshold eliminates any grays by either converting them to black (fill with ink), or white (leave as paper).

 

The mockup file is a small file used for colour reference. AVOID using Photoshop’s export option that will ‘save for web’. Often that option will change the colour palette of your image.

CLOSING NOTES

As screen printers, the only thing we can control acuratley in terms of transparent colours, are the colours sitting directly on the paper. The secondary colours created by the process, are just that, created organically and almost impossible to control.

[ insert screen printed version here ]