Wow, whoever originally backed this 19th century publisher’s binding should’ve really taken a moment to calm down and take a deep breath first before continuing. They really beat the crap out of it with the hammer!

Backing is  “the process of shaping a ridge or shoulder on each side of the spine of a text block prior to the application of the spine lining material.”

It was accomplished with the use of a backing hammer, while the book was held spine-up in a job backer (a special type of bookbinding press).