In book production, the spine is the key connection between the cover and inner pages. For a strong, lasting bond, this area needs to be free of anything that could interfere with the glue—especially ink.
Ink can create a barrier, preventing the adhesive from properly gripping the paper fibres. If that happens, pages may loosen or even detach over time.
When creating your cover design for your perfect bound book, we ask that no images, graphics or text are within 6mm from the inner spine area on the inside cover. When glued together the unprinted section of the spine won't be seen by the naked eye.
For more information on how to set up cross-over images for your cover pages in your perfect bound book, please see our article here - Tips on setting up a Perfect Bound Book with crossover images and text.