White Printing Inks
For most designers and printers the concept of white ink is new. Until recently, when you wanted an element of your job to print white, you reversed (or “knocked out”) the type from the background. That is, you didn't print anything within the letterforms, just around them as a background.
In short, white was the absence of ink.
But there are situations in which white ink is actually a necessity. For example, let's say you need to print white type on a dark substrate, like brown or black paper for an elegant and somewhat avant garde invitation. What would you do?
If the press run is long enough for offset printing (approximately 500 to 1000 copies), you might use an offset white ink, which would probably be based on titanium dioxide. This pigment is thick and has a high degree of opacity (covering power).
(Envision yourself painting a room white that had previously been painted a dark color. The white paint has to have good covering--or blocking--capabilities, or your white room will be darkened by the underlying paint. In fact, you might need to paint two coats or more.)
Offset Lithographic White Ink
One offset printer I worked with on a client's job a few years ago printed white type on a light beige press sheet
(just the lower-level subheads). The type was small, and the contrast between the press sheet and white type made reading difficult. Moreover, the type itself was not completely uniform (printing a completely even ink film using white ink is a challenge).
Some printers would have refused a job like this, instead suggesting screen printing as a more reliable way to get a consistent film of thick white ink for the type.
When my client was displeased with the print job, the printer, my client, and I put our heads together and came up with the following solution. Only the covers of my client's booklet had been affected by her choosing to offset print the white ink, so we removed the covers and kept the inside pages of the booklets.
My client then redesigned the covers. She had the printer create the brown background with ink (rather than using a beige paper stock). She only used white (in this case the paper white of the stock, knocked out of the brown) for larger, headline type. The smaller subheads that had been white on the first printing were changed to blue. They were much more readable when printed, and my client and her client were happy.
The printer split the cost with my client, and the amount my client had to absorb was charged “at cost,” significantly less than what the printer normally would have charged.
From this we can learn a number of important lessons:
- Printing white ink via offset lithography is a challenge. Sometimes the ink film is not completely even.
- Screen printing can do more to ensure an even ink film due to the thicker inks used.
- Sometimes it's better to create a “faux-white” ink by just not printing a certain area, or by creating an artificial tint for the surrounding paper and then reversing the type rather than using a colored text sheet.
- White ink is harder to read than a darker colored ink (whether it is actually white ink on paper or type reversed out of a darker background).
- Readability is even more problematic when the contrast between the background color and the white type is subtle.
- Therefore, it's very important to only use white ink (or reversed type) for larger, display type on a background with sufficient contrast to the text.
Digital White Ink
Enter digital printing: laser and inkjet. How do we print white ink using digital technology (if the press run is small or there's a need for variable data imaging)?
Titanium white is the basis for digital white ink as well as offset white ink. Unfortunately, the particles are heavier and larger than pigment particles in other inks (so the ink must be thicker, which can cause inkjet print heads to clog). The titanium dioxide particles also have trouble staying suspended in the ink vehicle (and must be agitated). Fortunately the technology is improving.
That said, some manufacturers only have the skill to underprint a uniform, flood white layer (for a backlit transparency, for instance, or between the front and back images on a static cling) rather than print precise, individual image detail or type.
In many cases, if the white ink must be completely opaque, more than one pass may be required on the digital inkjet press (white is available for xerography, but it's not commonplace). Two passes use more ink and take more time, so the process can become expensive.
Fortunately, the recent development of large, flatbed inkjet presses using UV-cured inks has given impetus to the development of new formulations of reliable white inks. People are demanding the ability to print on various non-white substrates, and this requires an initial coating of white as a base. According to Oce, a manufacturer of large-format inkjet presses, more than 90 percent of their customers opt for the white printing capability. It's becoming a core component of today's wide-format printing.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]