We can almost feel the frustration in the email when one of our customers can't seem to get the PMS color (the one they loved in the book and now are trying to print) to match. We wish we could say that we have never shipped out a color that wasn't an exact match to the book but hey, even we aren't that good! 98% of the time though something else is going on, and it usually boils down to one main reason in almost every case. But we'll get to that in just a minute.
Each color in the Pantone Ink Formula guide is printed individually as a spot color by the offset printing method. The ink is run to a specific ink density as checked by a densitometer. Boring scientific explanation: The densitometer measures the percentage of light reflected from the paper and the ink to help evaluate the proper amount of ink to be laid on the paper. Regular person explanation: The densitometer assigns a number value to the ink density; the higher the number, the thicker (denser) the ink film. Density (or thickness) of the ink film can drastically affect the look, color, shade of the printed ink. When matching a color, the ink maker has to have some standard to go by to make sure the color strength is right, the only real standard is the pantone guide. Love em or hate em, the whole world uses the pantone system. (Others have tried, but pantone is the last man standing).
When mixing our inks, we rely on the densities of the pantone book to be our guide. For consistency there's not really any other option. Most of the time, we mix the ink, proof it, check the density, tweak it, proof it, check the density, (you get the picture) and ship it out and someone happily prints their job. Occasionally though we get that email.
So, here's where we tell you what the problem usually is, if you haven't already guessed. Our inks, printed at the density specified by pantone are strong. Full strength colors (no transparent white) are typically not a problem. It's when we get into those colors that contain 50, 60, 90(!) percent transparent white where the problem usually pops up. Letterpress printers can have a hard time running their ink film down enough to get to the color they need. It can be extremely frustrating and lead people to believe that we've shipped the wrong ink or didn't do our job right. Believe it or not, even after decades of mixing ink some of the lighter colors can still eat up a lot of time to tweak and get right, so we sure don't want to have to mix them again. Rest assured, unless something crazy has happened the ink you receive has had a lot of attention paid to it.
So, what do you do? Some of our customers have found that ordering the color one shade lighter allows them a wider window with their density to achieve the color they need. Some folks put a note on their order to reduce the color strength of their mix (usually 15%). A lot of our printers keep some transparent white on the shelf to knock the strength down if it is an issue. Other things like the stock you're running on can also be a factor. Strong inks do have their advantages, such as quicker drying (less ink, quicker dry) better mileage, among others. We are here to help you; we want ink to be the least of your worries with the crazy printing process.