Large Format Printing: How (and Why) to Use White Ink

My fiancee handed me a food label the other day and showed me where white ink had been printed under process inks. She then asked me how the commercial printing vendor had produced the label. She asked if the white ink had been printed before the process color layers or at the same time. I didn’t have an answer, so I went online and did some research.

The Nature of Process Colors

I knew from many years in the custom printing field that process colors—cyan, magenta, yellow, and black—are transparent, unlike many spot colors, which are opaque.

I knew that the transparent ink films act a bit like filters placed over theatrical spot lights, although in the case of commercial printing inks the filters actually subtract certain wavelengths of light to produce the colors you see. Furthermore, I knew that if you were to inkjet print (or screen print) process colors directly onto transparent media (such as acetate) with no white background, nothing would reflect the light back to the viewer. Therefore, the colors printed directly on clear plastic would appear muted. Having a white background on the other hand would make the process colors printed on top of the white jump out, giving them more definition and brilliance.

But how could you do this on an inkjet printer? Would you first print a white layer of ink and then come back and print the process colors on top?

YouTube proved quite helpful. I found a number of videos showing white ink being printed in exactly the positions onto which the cyan, magenta, yellow, and black inkjet inks would then be printed. Due to the immediate curing properties of UV inks (inks “dried” instantaneously under UV lights), the inkjet print heads could travel back and forth, laying down the white undercoating followed by the process color inks of the actual artwork in one pass, as the printheads moved from the top to the bottom of the substrate.

When to Use White Ink

I could see in the videos how this process could add brightness and opacity that might be essential in the following projects:

1. 1. Backlit signage, in which the white would act as a diffusing layer under the colors. In fact, I had seen an example at a cosmetics counter, when the sales attendant had opened a back-lit signage case, showing me the white background behind the full color advertisement.

1. 1. Static clings. Not only would the bright white background increase the brilliance of the hues printed on the surface of the vinyl clings, but this would also allow for printing one image on one side and another image on the reverse side. Once placed on a window pane, the static cling could then be viewed from either side.

1. 1. Standees with clear panels. In a prior blog article, I had mentioned the standee for The Lone Ranger, which included clear acetate panels onto which images of the two main characters had been printed. From the back of the panels, you could see white ink covering only those areas over which process color images were visible from the opposite side.

1. 1. White backgrounds on inkjet printed shirts. I saw another video in which an inkjet printer was printing white letters on a blue sweatshirt. Beyond the intriguing nature of the video, which showed exactly how ink could be printed on a fully made piece of clothing (which was positioned firmly on an unmovable platen), the video also made me think of other garment printing applications.

      After all, if you’re custom printing a bright image on a black sweatshirt, a background of white inkjet ink would prevent the black cotton substrate from dulling down the transparent process colors printed on top.

      At the beach last summer, I had seen numerous shirts like these, on which colors could be much brighter than the fabric of the dark shirt itself. I knew this could be done with custom screen printing, and I had seen similar techniques used to offset print process color images on dark paper (with an intervening layer of white, on top of the press sheet but under the process colors).

      But the YouTube video showed exactly how inkjet technology could do the same thing with the same result, allowing white ink to be positioned and then immediately followed, line by line, pass by pass, by the brilliant process color images on top.

This entry was posted on Monday, May 5th, 2014 at 6:20 pm and is filed under Large-Format Printing. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.