Thanks all for your questions and suggestions. Here are a few selected answers.
Is it possible to show a picture of the printed result?
Have you previewed with a proof-profile somewhere in your workflow?
Working on a picture of the result. I soft-proofed to the extent possible - ie sRGB which is what LR converts to prior to upload. Of course its not possible to soft proof to blurbs CMYK profile. I should say that while there are a few image where the color is wrong, I am for the most part satisfied with the accuracy of the color reproduction.
Before ordering had you seen a Blurb book before ? Had you proof printed the images via a desktop printer ?
The "graininess" you're seeing may just be the halftone like screening (a bit like inkjet dither patterns, but larger) on all output from the HP Indigo.
No, I have not seen a printed result before. Yes I did print some (not all) of the "problematical" images. I have an Epson 2880 printer and I printed either at the same size or larger than the book. I did not observe the same problems.
You probably have a point about the "graininess". For some reason I assumed that the blurb printers would be higher quality/more accurate than my own. Maybe, I am wrong there. I do not know much about the HP printers they use. See also below about paper quality.
Things to check. First export to pdf from LR and check the pdf file to make sure it is not a problem with your images. Second after uploading to Blurb but before ordering do a preview of the whole book on the Blurb website.
Good luck. Final thought - what paper did you choose for your book? I only use the more expensive photo pearl option.
I did export to pdf and did not observe the same issues. Nor on the site preview. Of course the screen resolution is not the same but ... no, nothing observable.
I used the intermediate cost pearl paper.
Do you see the vertical banding running consistently through all the images?
Oddly enough, no. Just on a few images. But maybe its less visible, depending on the colors etc.I assume they do a single print run. I definitely do not see it in my own prints