For some time I have seen and enjoyed the LensWork magazine. I understand it is printed in duotone as opposed to four-color printing. I have this question: Why duotone and not four-color printing?
Secondly: One color is of course black – what is the other color?
Thirdly: Have you any Lightroom preset that emulates this specific variation of duotone that LensWork is using?
— Peter Høvring
There are several reasons to choose duotone over four-color printing, chief of which is quality. To be even more specific, consistent quality. What you refer to as "four color" printing is technically CMYK printing, the most common printing industry practice. By dividing full color images into the four colors of Cyan, Magenta, Yellow, and blacK (hence, C-M-Y-K), a reasonable number of the colors of the full spectrum rainbow can be simulated. Reasonable, but not all colors. (Aside: those colors that can be reproduced are said to be inside the "color gamut" of these inks, those that cannot be simulated are said to fall outside the color gamut.) CMYK printing has been an industry standard for decades and suffices for most printing needs, particularly where absolute color fidelity is not the most important issue. It's good enough for 99% of all commercial printing.
Except for us picky photographers for whom color and image fidelity are all important.
Photographers have recognized that the inherent limitations in the range of possible colors that can be printed using just CMY and K inks. CMYK printing will change the color fidelity of their finely crafted color photographs. Other color schemes have been pioneered for a broader color gamut, probably the most common ones are Pantone's Hexachrome (six colors) color printing for offset commercial printing and the current batch of inkjet printers for personal use that employ extra colored inks to expand the range of possible colors that can be produced. (Additional background information on color theory and printing, and some background info from Epson.) Color photographers can be a bit more satisfied with this expanded color gamut. If you want to see an example of simply superb color printing, buy Bill Atkinson's book Within the Stone. (Bill's website.) Even if you aren't interested in photographs of stones, you will be amazed at the color fidelity in this state-of-the-art printing example.
But what about black and white images? If we want a warm-tone image in LensWork, why not just print using CMYK with a warm-tone tint?
The answer is consistency. The press that prints LensWork is capable of printing 8,000 sheets an hour. They zoom through the press. You can just imagine the challenge of keeping the ink levels in perfect balance throughout the full press run — fighting things like ink temperature and viscosity, plate coating consistency, paper thickness variations, humidity, etc. It's a daunting challenge. If the colors drift even the tiniest bit from dead center, black-and-white photographs can quickly become ever-so-slightly-blueish-black-and-white. Or, a bit too cyan, a bit too magenta, a bit too yellow. Any of you who have done a black-and-white book from Blurb.com or Lulu.com know what I'm talking about. A dead neutral grayscale is almost impossible to achieve.
Now, if it's difficult to accomplish this during the course of a single press run, imagine the difficulty of achieving consistency from issue to issue of a bimonthly periodical, year after year. Yikes.
Instead, we use duotone printing which employs only two inks — black and, in our case, Pantone Warm Gray 11. These two inks can be applied year after year and they will always be exactly the same "colors" because they are made for each press run to exacting spectral standards. If either of them drift a bit in printing — an inevitability — the color of the printing doesn't shift. Since there is no cyan, magenta, or yellow on the press, these bad boys can't rear their ugly heads and mess anything up.
Just as important, duotone printing allows an overlay of the two inks that build to a blacker total density than either of them are capable of by themselves. This increases the richness of black and white images and, with today's presses and stochastic screening, rivals the black density of the best selenium toned gelatin silver papers from a traditional wet darkroom. Amazing.
Duotones are tricky to use because they cannot be proofed except on press. This can be an expensive learning curve, especially for a single book press run. Thankfully, with a bimonthly periodical, we have a chance to tweak and adjust if we need to every sixty days. And — no small consideration — because we use two less ink plates than CMKY printing, there is less press setup and fewer printing plates to pay for.
So, quality — comprised of consistency, better black density, and control — is the short answer to the benefits of duotone printing.
As to presets, here are a couple you can try. If you have a properly calibrated monitor, they'll be a good place to start, but keep in mind that perfectly matching a duotone on a printed page and a backlit monitor image is going to be almost impossible. Nonetheless, here is the Lighroom preset and the Photoshop B/W adjustment layer we use in-house.