Why are Pantone Bridge CMYK levels slightly different between Coated and Uncoated?

Question

Pantone Solid – Shows same formula, different outcome.

Pantone Bridge – Shows different formula(C 0,0,56,0 vs. U 0,0,50,0) and different outcome?

So Pantone Solid defines formulas for their spot colours. The C or U show what that formula would look like on the respective finish while the mix remains constant.

Pantone Bridge provides CMYK matches for these Solid colours.

My question is if C and U are for defining how the same ink-mix looks on different finishes why does Bridge have different CMYK values for C and U?

My best guess is that Bridge U is trying to match Solid U and Bridge C is trying to match Solid C? Why wouldn't they just take the same approach as Pantone Solid and have Pantone U be defined by how the same mix looks on Uncoated?

Answer 1

There are two different things going on here, and both are unrelated.

The first is that inks look different when printed on coated versus uncoated stock.

The formulas are the same. The only real* difference is the paper coating. On uncoated stock, inks tend to absorb into the paper, on coated stock however inks sit on top of the coating, and dry by oxidization. This results in a slighly more vivid colour on coated stock.

Secondly, for the differences between solid and CMYK colours, it's because CMYK colour is only an approximation of a solid colour. Some solid (or spot) colours can't really be achieved accurately using CMYK. CMYK printing is a different printing process from printing Solid Pantone colours. Because of this, they will never look the same. There's more info here on another similar question I answered.

I think the reason the CMYK values differ for the Bridge CMYK colours (for coated versus uncoated) is because the guys at Pantone have tried to compensate for the problems of simulating Solid colours using CMYK process printing on coated versus uncoated stock. Because it's a different process, if they left the CMYK values the same, the colours would look even more different on different stock.

*Note: I say only "real" difference, but sometimes printers alter the formulation of an ink depending on the stock or different processes involved in printing. This is not something that affects colours or that clients/designers generally need to be aware of. It can involve the use of additives or using different bases such as oil or rubber based inks, etc.

Answer 2

When inks are applied to coated paper, they tend to "sit up" on the paper stock and dry by oxidation. When they're applied to uncoated paper, they dry by absorption into the paper stock so tend to die back slightly. This affects the depth of color that you see when applied to either coated or uncoated paper.

Using process color to simulate PMS spot colors is affected by the nature of the stock. On top of that, process simulation colors tend to be "dirty" when compared to spot colors. You'll never get an exact match and some colors are worse than others.

What the chemists/engineers/mixologists are trying to do when changing the values is compensate for the above variables.

Although a good pressman can sometimes compensate for these variables depending on how much ink he lays down on the sheet, the swatchbooks are providing the most realistic and consistent looks.

Keep in mind that printing is chemistry. Sometimes you have to play with the formula in order to get what you want.

Answer 3

Pantone color materials are much less transparent than C, M and Y printing colors. They do not show the underlying paper as long as there's enough color. But practical print machines cannot handle that much, so uncoated (which suck a part of the ink between the fibers) and coated papers still produce a little different results with the same Pantone color material mix as the book shows. Otherwise you wouldn't need different books.

The "uncoated" and "coated" books are organized to show the result with the same Pantone color material mixes, but because the result is a little different, the names of the seen colors are separated with letters U and C.

CMYK print colors (except k) are transparent color filters - the result depends heavily on the underlying paper.

I'm not at all sure which Pantones can really be created with CMYK. As far as I know there are numerous colors which are impossible for CMYK. Metallic glosses are not the only ones, there are also many Pantones which have too high chroma (=colorfulness, deviation from grey).

The CMYK versions of Pantones should be seen as "best efforts" - not perfect, but as colorful as CMYK process can create. The best effort needs different CMYK numbers on differently color sucking and reflecting paper. The printed book of the subject shows the best effort and what you can get with it.

Check this text for more details: https://www.advancedlabelsnw.com/blog/3-misconceptions-about-pantone-colors-for-labels