Since many printed matter contains spot colours such as Pantone or HKS, the question often arises whether these colours can be proofed at all. The answer is “no”. Only an approximate simulation of these colors is possible.
The reason: Each special ink is a specially mixed, “real” ink and therefore cannot be mixed from the 4 printing inks (cyan, magenta, yellow and black).
Today, modern proofing machines have up to 12 different printing colours and, in addition to the classic primary colours, also have, for example, orange and green and violet as real colour pigments in the machine. Proof printers such as the Epson SureColor P9000V are therefore capable of displaying significantly larger color spaces than, for example, ISOCoatedV2. The spot color simulation in these devices is therefore sometimes very good when controlled via a Contone driver, which can access the entire color space of the proof printer. Epson himself points out, for example, that “98% of all Pantone colors” can be covered. This may be doubted, but a number of over 90% of all Pantone colors is realistic from our point of view.
In the past, Pantone and HKS colors were simply converted by the proofing systems to CMYK and then simulated in the standard color space, i.e. mostly ISOCoatedV2. The representation of the colors here is mostly completely insufficient. For the reproduction of Pantone and HKS colours in a proof it is therefore immensely important to have a modern proof printer with many colours and a high colour gamut and a modern proofing software which is also able to precisely control the printed gamut.
Differences in the quality of the simulation of spot colors can quickly be seen in the different printing systems: If the proofing service provider prints with an older 6-color or 8-color system (Cyan, Light Cyan, Magenta, Light Magenta, Yellow and Black or Light Black), spot colors are simulated worse than, for example, with a modern 11-color system with Cyan, Light Cyan, Orange, Yellow, Magenta, Light Magenta, Photo Black, Matte Black, Light Black, Light light Black and Green.
The higher simulation quality of the spot colors is generated by the fact that orange, for example, already exists as a separate color and does not have to be mixed from magenta and yellow before the spot color simulation.
Of course, it must be said that there are limits, especially in the area of metallic or fluorescent colours; these colours are currently not reproducible in proofing.
The spot-colour simulation of gradations is also critical
In most proofing systems, only the 100% values of a Pantone or HKS color are underlaid. If, for example, a font logo with 100% color application of a Pantone color is to be simulated, this is precise and is well represented in most proofing systems.
However, it becomes more difficult if the logo contains not only 100% areas but also a 30% Pantone colour area, since this is not defined in the proofing system, but is simulated by the proofing system. In some cases, considerable deviations from e.g. HKS colour fans can be observed.
It becomes even more difficult if, for example, a grayscale TIFF lies on a 100% HKS area and overprints. For the graphic professional it is immediately comprehensible that the HKS surface simply has to become correspondingly darker at this point due to an overprinting 30% black. However, the proofing software must recognize this effect correctly, calculate it correctly and then simulate it correctly with the 11 colors available from the proof printer. It is easy to understand that countless errors can occur. And the supreme discipline: 7-colour Pantone files with lots of overlaying and overprinting Pantone colours or HKS colours with overprinting CMYK elements can at best be calculated even by the most modern proofing systems, but can by no means be colour-accurately simulated.
The bad news is that a proof with spot colors is therefore never as color-binding according to the current state of the art and varies more depending on the proofing system.
But the good news is that spot colors, especially solid colors, can now be simulated well by modern proofing systems. A modern proofing system therefore also offers the possibility of getting a realistic impression of spot color prints at a fraction of the cost of a test print on a offset press.