black and white versus color-profiles

What kind of printing technology will be used?

Printing black & white images with a standard CMYK profile on an offset press very often leads to a color cast – usually magenta, sometimes cyan.
I have gotten very good results using a custom CMYK profile that uses less CMY inks and more black ink. A properly calibrated press and a skilled operator also helps.
 

Digital printers were also problematic in the past, but they may have improved in recent years. The last time I had something printed digitally was about 10 years ago.

In either case, I recommend having a test print made before sending the whole book for printing.

Thanks to all of you:-)

But I do have another question concerning the workflow of my photo book. It seems to be strange that the icc-profile I need for the paper of choice comes in CMYK only, although RGB is demanded for the book. Apparently lightroom cannot handle CMYK and is not able to find the profile at all. The only way seems to use photoshop in cmyk and convert into RGB (very well planned by the book printer...). Unfortunately ps is too expensive and in most cases lrC with nik-suite are completely sufficient.

As I understand it, Lightroom Classic always exports a three-channel RGB file even if the original source file is one-channel grayscale, and there may not be any way around it. I noticed this when seeing exported grayscale scans of B&W film take up more space than expected, since a three-channel file is larger than a one-channel file.

Even in Photoshop, you have to be careful. Although Photoshop has many ways to save a JPEG, most of them always produce RGB. One way that can preserve single-channel grayscale in JPEG is to specifically choose File > Save As and choose JPEG. But for example, if in Photoshop you choose File > Save for Web, the JPEG will always be RGB. 

(Apologies if you got a notification that this got marked Best Answer by me. I hit that by mistake and then reversed it.)

In Lightroom, as in many other software, it is possible to de-saturate a full colour image’s original hues,  so that every pixel shows a shade of grey. There are several ways to do this, but the Lightroom image editing “world” then still remains full colour capable.

One may de-saturate original hues by applying a Basic panel adjustment (or HSL, whatever) - and this is equivalent in effect to choosing a black-and-white profile. But it is important to note:

• if each pixel is given an equalised R, G and B value that still does not guarantee a neutral-hued appearance will result when printed / viewed / whatever. The output method may itself produce some sort of colour cast anyway, in other words. Even if printing uses a truly monochrome technology / a display technology operates solely in levels of brightness.  
• Even if original picture hues have been fully de-saturated, that does not guarantee Lightroom Classic will always output pixels with equal R G and B values. They are still produced in a full-colour editing environment. There are opportunities to postprocess in a deliberate colour cast for aesthetic reasons (Color Grading, say, does not obey any B&W processing profile used) - also, to impose for calibration reasons an output profile which then tweaks the RGB values for each pixel in the output file.

all pixels in histogram do have same values! Some photos still seem to be slightly different, but only R70 G71 B69.5 e.g.. I think that won´t make any difference, at least for my eyes... 

thanks, I understand.

Due to book printer`s FAQ (translated from german) : If a grayscale image in the RGB color space does not have identical color values, a color cast may appear in the image. You need to check whether the RGB values are identical and adjust the image if necessary before placing the order.

To be honest I do not know what to do exactly...

“For printing, I need RGB files that contain only neutral gray values (no color information) in order to avoid any color cast in the final print.”
 

That is not possible, by definition. RGB images contain three channels, R, G and B. That is the definition of RGB. A real greyscale image contains only one channel, but then it’s a greyscale image, not an RGB image. An ‘RGB greyscale’ image contains three identical channels, but that means it still contains three color channels, not a single greyscale channel.
 

Lightroom cannot export true greyscale images, but Photoshop can convert RGB to Greyscale. Do realise that the book printer must support greyscale!