Are spot colors limited and why CMYK mix is not treated same as spot color mix?

Question

I read this article today. I understood a few things, but few remained unanswered.

The article mentioned 18 basic colors. The things little confused me after that line. I assumed Pantone have only 18 spot colors currently.

So 18 basic colors are spot colors.

Okay, that's about spot colors.

Now, in process colors, I understand so far that colors produced while printing by using C, M, Y and K inks are called process colors.

Also, the article mentioned that mixing of colors produce spot colors (if I understand correctly). So, when CMYK is also a mixing of colors and results in new colors, I wonder why the colors aren't called spot colors.

Given all that, it may seem a lot of doubts, but the ultimate aim is to know the true meaning of spot colors and why CMYK mix is not same as spot color mix.

Answer 1

Simply:

CMYK is not mixed. A printing process generally do not mix colors. It is kind of the holy grail of printing processes but it does not really exist as of yet.

What happens instead is that printing processes layer transparent inks on top of each other. Each ink only being able to produce either full ink color or no ink color. The indeterminate colors are achieved by alternating these cells of of ink or no ink on top of each other. Result is what looks like some value between the colors and white but is no where as rich as a mixed ink. We call a super cell of printer dots that produces a apparent color we call a print raster.

Spot colors on the other hand are mixed. So if you want lime green no problem lets mix lime green. You can again not print different mixtures, just rasterize different spots or process colors together but if all you want is lime green then you get it exactly as it is.

To understand the biggest difference between the two you would have to work with retail packaging. See in retail you have packages form different batches, possibly form different factories side by side. Now if there is a small but discernible color variation between these batches people would act as if the other batch is somehow tainted, they would gravitate towards the other batch, this leads to a lot of lost sales.

Now process color is more fragile when it comes to reproduction than spot colors. Mainly because reflected surfaces react with ambient light. The inks have some color spectra, humans of course do not see spectra. However when the surrounding light around reacts with the different inks something special can happen. They can under some lights seem the same and different when seen in other light condition. So while CMYK can reproduce same color under same light a spot color can reproduce the same physics as the other if substrate is same. Also if you are willing to mix custom proportions you can possibly get same color on other substrates.

You also get a cleaner color, and a wider gamut if you are willing to mix colors. You also get more even surfaces of same color and possibly gradients too. Also it is possible to dye plastics or fabrics with some spot systems so then you can order material in your exacting color, none of which you can easily do with process colors.

Answer 2

TLDR: No, spot colours are not more limited than CMYK, and they aren't treated the same because they are different printing processes.

Process printing (or CMYK printing, also sometimes called full-colour printing) uses separate inks. They aren't mixed.

The inks are layered onto the paper, usually using halftone dots to build up a pattern of dots to simulate a solid colour when viewed at normal viewing distances, or often as not for reproducing full-colour illustrations or photographs. In offset lithographic printing, this usually means using a press with four print heads, and four printing plates, one for each colour, or sometimes using one or two heads with multiple passes through a printing press.

A typical 4 colour process offset lithographic printing press, showing the four colour heads (CMYK), and ink ducts, which supply ink to the rollers, and subsequently to the 4 printing plates, and the image is transferred to a rubber blanket, and then onto a sheet of paper under compression between the blanket and a steel cylinder.

A spot colour is printed using one single ink, often made by physically mixing different base colour inks to a formula from a Pantone guide book - a bit like the same way you'd mix some base paint colours to get a new colour.

Mixing a spot colour ink

Each spot colour is printed using only one printing head, and one plate, and typically with solid areas of ink, although it's possible to use them with halftones too. Spot colours have a wider gamut than CMYK colours, and there are spot colours which have no equivalent in CMYK - for example, metallic colours, or fluorescent colours, or inks with pure pigments such Reflex Blue, which is notoriously difficult to reproduce in CMYK.

Sometimes very large printing presses have more than 4 print heads, allowing the extra ones to be used for spot colours. Multiple spot colours are possible, and spot colours can also be layered on paper to create different colours.

You will likely need to use a magnifying glass to see it, but this is what a printed process colour looks like compared to a solid spot colour close up.

Answer 3

Alright a typical printer has 4 cartridges, CMYK. It looks kinda like this with the black cartridge usually a bit larger because it gets used more frequently:

If you print on this printer and the image has green in it then its going to put tiny dots on the paper of both Cyan and Yellow in order to make that green. This is what CMYK process is.

Pantone and Spot Colors in general can be thought of almost like this. You have your CMYK and then you have a pre-mixed precise color. Say its a Green spot color. Now you have a precise green and don't need to mix Cyan and Yellow to attempt to get the right green. You just put down the already mixed green.

This is very expensive and while I have no stats to support it would venture to say most print shops cannot even do spot colors like this.

Let's pretend your Coca-Cola and typically always use a very precise spot color for your red. But if you're Coca-Cola you may at times be using a printer that doesn't do spot colors. Internal memos likely are printed on basic office printers. In that case they approximate their signature red using as close a CMYK equivalent as they can.

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Another key thing is some colors cannot be produced at all within the CMYK space. Neon colors for example require the use of a neon pigments. This would be another example of a spot color. See Alan's answer here: https://graphicdesign.stackexchange.com/a/4473/2611

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Now regarding the 18 base colors it talks about. They use 18 base paints, which they mix in industrial mixers to precise ratios, and then that mixture becomes for example Pantone 1925C.

Answer 4

The Pantone Matching System is a colour space. Like the RGB colour space that you're probably familiar with on computers, CMYK is another colour space for printing. By mixing or layering together the colours yellow, magenta, cyan, and black, you can obtain many colours. But like all colour spaces, it has limitations. No matter what you try, you cannot obtain white ink by combining yellow, magenta, cyan, and black ink. If you're printing on white paper, that's not a problem. CMYK lets you say "put no ink here and the white paper will be visible". But if you're printing on another colour, such as uncoated cardboard, then to have white you need another colour space.

The Pantone Matching System is another way of specifying colours. I expect that it can completely cover the CMYK colour space, but it also has many colours which cannot be represented in CMYK. If RGB is a three dimensional colour space, and CMYK is a four dimensional colour space, PMS could be considered an 18 dimensional colour space. PMS not only includes regular colours like yellow and blue, but also metalic and neon inks, which cannot be represented on a computer screen or by CMYK printing. (And even PMS can't represent all possible inks, it doesn't have white for example.) Furthermore, Pantone specifies different recipes for producing inks depending on whether you are printing on coated or uncoated paper. It is designed for large-batch printing where you communicate directly with a printer and tell them the individual inks you want. The PMS system lets them reliably mix the colours you request (which is why there doesn't need to be a Pantone white - you can just tell the printer you want white, and they'll already know how to produce it.)

A Pantone spot colour is an ink mixed by the printer, possibly by the bucketload. It does not get mixed or layered in the printer as in ink jet, laser or offset printing, but is pre-mixed and fed into the printer as a finished colour. This ensures the colour is completely consistent, and reduces the likelihood of misaligned printing (at least for a single colour; it is still possible when you're using multiple spot colours.)

Answer 5

A factor not yet mentioned is that the cyan, magenta, and yellow inks used in a CMYK process are deliberately chosen so that, as nearly as practical, overlaying cyan on magenta will yield blue, overlaying magenta on yellow will yield red, and overlaying cyan on yellow will yield green. It would be possible to have other inks which, when printed alone, appear identical to cyan, magenta, and yellow, but which when overlaid with each would yield different colors.

Spot colors are often not chosen for purposes of being overlaid with other colors, and the effects of overlaying them may differ from what the "color table" would imply. It's possible that two printers have red inks and orange inks that look identical by themselves, but which when overlaid yield very different results. For example, an orange ink that transmits red and green light, but absorbs light at intermediate wavelengths, may be visually indistinguishable (in isolation) from an one that absorbs a lot of red and green but transmits intermediate wavelengths, but overlaying the former with red would yield a much darker result than overlaying the latter.

Unless one specifies how spot colors must behave when mixed, there's no guarantee that a document which overlays spot colors will appear consistent when processed by different printers using different inks, even if the colors of the inks, in isolation, would match perfectly.

Answer 6

Process or CMYK colors are, as you've seen, colors mixed from C, M, Y and K inks.

Spot colors are generally printed using a specific color ink mixed from one of the 18 Pantone inks that you mentioned, though sometimes printers use a formula that allows them to mix a spot color (or an approximation of it) using CMYK inks.