Black on black

It is the non-colour colour, enigmatic and seductive. But far from easy to obtain and reproduce. More than "black", we should talk about "blacks" because, beyond the printing inks, there is also the black management of the graphics or DTP programs, on which those inks derive and depend. Here's what you need to know to create black printing projects.

By Lorenzo Capitani | on PRINTlovers #91

Black as night, darkness, the cosmic void; black as the witch's cat, the Frisian horse's coat, the raven and the panther; black as blackberries, elderberries and currants. Black as coal. There is a lot of black around us! In reality, there is no such thing as black, in the sense of a colour with zero luminosity. Perhaps the only thing that is absolutely black is the black holes up there or, in terms of human affairs, the blackest black, the blackest substance ever created, composed of carbon nanotubes, developed in 2019 by MIT in Boston: capable of retaining 99.995% of light, it has surpassed the Vantablack patented by the British company Surrey NanoSystems, with which BMW has created a special paint for its X6 Vantablack. But black is also the colour of newspapers, photocopies, books, documents, ink comics: in short, it is the colour of printing par excellence and electronic ink.

Black as ink
Black is the colour of text but also of images when only one colour was printed, and above all, it is one of the colours of four-colour printing. Cyan, magenta and yellow, which on their own would theoretically produce black, even at maximum intensity, only produce a very dark brown – bistro - without black. Jacob Christoph Le Blon, painter, engraver and inventor of a four-colour copperplate printing system, had already realised this when in 1725, in his volume Coloritto, he reproduced a portrait of a young woman by superimposing three inks (blue, yellow and red), adding a fourth plate inked in black to improve the image.
The easiest way to obtain black in offset is to use the black ink, the one in the last letter of the initials CMYK, where the K does not refer to blacK to distinguish it from blue, as the legend has it, but to the term "Key", because the black plate is the "key" one, the one used as a reference for the alignment of the register between the plates of the other three colours.

Black and beyond
Even newspapers, once the undisputed kingdom of black, use colour, despite their print output and paper. And if we exclude book publishing - the only one for which it makes sense to print only in black - in the world of commercial printing, between new technologies and digital, the myth of using just one colour to minimise the cost of printing has also fallen. In the age of imaging, converting everything to greyscale with colours reduced to a single channel made by the black screen, with more or less smooth transitions depending on the linework, makes everything look like a well-made photocopy.
The addition of black in print improves colour rendering by adding more contrast and depth to images, allowing fuller blacks, widening the gamut of colours obtainable towards darker colours and making the control of the balance of the other three colours less critical, i.e., as they say in the jargon, stabilising the grey axis.
Yet if cyan, magenta and yellow alone cannot produce black, it is also true that black cannot do without them. Gianni Camusso, senior graphic designer and former deputy art director of Mondadori Libri, who has worked with numerous publishing houses, explains: "I would start by distinguishing the black of a background or lettering from the black of an image. Perfect for text, it is not sufficient in terms of coverage for large surfaces, such as a cover, or work where the quality of the images is essential. Black ink, even at maximum density, appears washed out and drained, almost grey, on backgrounds alone", especially if the paper tends to absorb it, or again, if the perforation is not set up correctly and the overprinting leaves any underlying graphics visible, "but in this case, the software automatically overprints it over the other colours on which it rests".

I see black
Generally, to make black look good, it is best to create a black reinforced by a second colour or made up of all four inks, creating a so-called rich black. It all depends on how we are going to print, the type of job and the budget.
Camusso continues: "In the case of a background that will contain negative text, it is better to limit the enrichment of black. That's because you want to avoid the out-of-register effect that would affect readability, as we often see in magazines and journals. It is always difficult in printing to ensure that the four colours are perfectly in register and that white texts can be clearly read on a four-colour background. On solid backgrounds, you can make up a black reinforced with 50% of a second colour, but this will inevitably have a dominant effect depending on the colour chosen: "enriched with cyan, it will look imperceptibly cooler, warmer with red", while using yellow it will have a more golden hue.
If you wish, you can also take advantage of the spot colours made available by the Pantone system and double the black with a second ink from the black range: a ploy that makes the black colour more intense and compensates for the risk of capers on solid backgrounds. There is an embarrassment of riches to choose from: a search on the PantoneConnect platform is enough to find at least fifty.

The colours of black
Two blacks undoubtedly improve things, even in the case of b/w images printed in 4 colours. But it is necessary to work in prepress, building a second black, called "skeleton" or "fallback" black, from the CMYK image, duplicating one of the channels (almost never yellow) and, in the curves, lowering the shadows to create a new spot colour that fills and designs the halftones. But you can do more, especially if you are looking for maximum quality: add a grey as a spot colour. If you print with two blacks and a grey, the image is first converted to a 4-colour b/w; then you will generally use the cyan channel to print the halftones with black ink, the magenta channel (at 80%) for the grey and the black channel for the skeleton, eliminating the yellow which does not draw and makes it dirty. Deciding in advance which of the greys to use is difficult because the on-screen simulation does not actually render what the print will look like, all the more so when using a Pantone. For this reason, it may be advisable to agree in advance with the printer and be prepared to patiently chase the desired result at start-up. Of course, if you are looking for special effects such as sepia, you can use another Pantone.
"When I only have the four-colour process available to print a b/w photo," explains Camusso, "if the image is already in b/w, it generally already has contrasts that the photographer originally studied and it may not be necessary to intervene, while if it is converted from a colour original, it will almost always look flat and without much contrast. It will then be necessary to intervene in the curves to restore depth to the blacks and light to the whites for greater three-dimensionality. In both cases, however, I always convert the image into four-colour to have fuller blacks, taking care not to exceed 300/320% in the sum of the colours, measuring a black point of the image".
For the most neutral b/w possible, starting from an RGB image, you can convert it to CMYK with a high GCR (Gray Component Replacement): in the image, it will work much more with black and less with the other colours, improving neutrality.

Deep black
Of course, the most practical solution to achieve a nice full black in backgrounds is to create a so-called rich black made from the 4 four-colour process colours in different combinations. Each graphic designer has their own recipe: Camusso prefers C40, C40, Y40, K100, but also used are C30, M30, Y40, K100 or even C50, M30, Y30, K100. There is not much difference; the important thing is not to exaggerate with the percentages of inks which, added together, should not exceed 310% for a coated paper. This threshold, which is in any case indicated by any preflight system, depends on the type of substrate and represents the maximum quantity of superimposed inks tolerated (TIL = total ink limit) before giving rise to the phenomenon of rejection, which occurs when the paper is unable to absorb the inks. Certainly, a black made this way will appear full, uniform and well covering, but what about the register? It depends on where it is used: rich black should not be used inappropriately for fine graphics or small texts for which only black should be used.

It's easy to say black
In short, more than "black", we should talk about "blacks" because, beyond the printing inks, there is also the black management of the graphics or DTP programs from which those inks derive and depend.
In Photoshop, apart from flat black (C0, M0, Y0, K100), there are two different basic compositions for four-colour black: C75, M65, Y60, K80 with 280% opacity, which is obtained by converting flat black from RGB to CMYK, and the so-called Photoshop black or C91, M79, Y62, K97 with 330% opacity, which corresponds to the maximum achievable black (Lab* 0, 0, 0 - RGB 0, 0, 0 - hexadecimal 000000). In InDesign, where the basic black is flat black, and there is no possibility of conversion between document colour spaces, it will be at the moment of creation of the PDF that, according to the settings, the correct conversions to four-colour process will take place: flat black will remain K100, 4-colour blacks will maintain their compositions, and any blacks in RGB will be converted proportionally to CMYK values (e.g. RGB 30, 30, 30 = C75, M65, Y60, K80). But the mistake that should not be made in InDesign is to use the black called [Register]: this is a colour sample, which cannot be modified or removed, obtained from the maximum percentage of the four colours, which is carried over to each channel and is used for printing marks, such as register marks, cut marks, page information, indentations and so on.
Remember that what you see on the monitor is not what you will print, so set the black appearance in the InDesign and Illustrator preferences so that flat black looks like a dark grey and rich black is actually black.

Printing black
But let's get down to printing. In offset, you often see backdrops or text with large bodies printed in black with clearly visible transparent images underneath. It is easy to see this on the screen when you are setting the page, provided you leave the overprint simulation activated. Black ink alone, no matter how rich it is, cannot completely cover the underlying screen of the other colours. Rich black helps, but when you can't use it, you can get around the graphics program settings by setting black only at that point in perforation and not in overprinting so that it "pierces" everything underneath. Be careful, however, that in the creation of the pdf or the ripping phase, you do not restore the initial situation.
In digital, the logic does not change, but there are greater technical possibilities precisely because it is possible to intervene as required copy by copy, with maximum precision. With Indigo technology, for example, it is possible to create rich blacks to obtain excellent coverage; where the black channel is only made up of 100%, it is possible to print the colour several times (from 2 to 16 times); in addition to this function, it is possible to decide to rip (reprint) only K100 so as not to vary the colour on a job or to reprint the whole K100 and its halftones.
Moreover, it is much easier to intervene precisely on the quantities of ink on the texts and images to reduce the effect of black closed that sometimes the digital gives, especially in the shadows and in the very dark b/w. When ripping, the images can be sharpened to provide more detail or smoothed to provide further softness to the shadows' colour transitions. The concept of a second black reinforcement is also present in digital, especially for rendering b/w images. By preparing the work in two colours (black channel + light black channel), you can obtain high-quality prints without another colour's predominance.



| Interview |
Printing black digitally
Printing black digitally has features in common with offset, but it also has its own peculiarities: we talked about it with Fabio Galimberti, Solution Architect for HP Indigo Division.

What is the best practice for printing a b/w image digitally?
Start with an RGB file. HP Indigo uses an algorithm that automatically transforms the input file to 2 separations Black + light Black for black and white images; otherwise, the algorithm will transform it to 5 separations CMYK + light black for colour files.
Light black ink was initially developed to meet the needs of the photographic world to achieve very high quality in black and white. Typically, to print this kind of image, we always worked with four-colour files, but the final result often had a predominance of yellow, magenta or cyan; it was tough to have a neutral image in grey tones that would easily bring out all the details. HP Indigo overcame all these problems simply and automatically, initially creating an algorithm that worked only for two-colour black and white; then, as the demand shifted to four-colour, with a second algorithm for colour images.

What are the differences between printing quality black in digital and offset?
With HP Indigo, we have no differences; our technology allows us to repeat the black channel several times, which means that the separation has a double pass of ink. If I want, I can also do this on all the separations in my work (CMY).

In digital, how do you avoid excessively closed blacks in the shadows and very dark b/w?
Being a digital offset, we use the same printing philosophy, working on the black channel compensation curves and correcting the opening of the shadows where necessary.

How do you prepare the file to print a deep, neutral quality b/w?
Basically, in two ways. The first is automatic, without prepress operator intervention: just copy the file inside the DFE Indigo, and the HP Indigo algorithm does the separation for both colour and b/w jobs. Or manually, by creating 2 Black + Light Black channels via Photoshop: in this way, the graphic designer will decide where he wants the second colour printed. Again, in the end, I will copy the work into the DFE.

How many blacks are there in digital in terms of 4-colour and special blacks (Pantone or special inks)?
We have no limits; the HP Indigo presses can print up to a maximum of 7 colours simultaneously: being Pantone certified, I could insert three different types of black. In addition to Pantone, I can insert custom colours (Coca-Cola red, Poste Italiane yellow, to give a few examples). All you need is the LAB value and the type of paper you intend to print on, and HP Indigo can provide the desired ink. We also have other special inks: a new white ink with high opacity; an invisible yellow, whose graphism I can't see with the naked eye, which is activated by UV light; a fluorescent pink ink; light cyan and magenta inks; and last but not least, a transparent ink that allows you to have a spot varnish effect (only visual and not protective).