For rare books restoration and conservation purpose; in many cases, spine lining, and animal glue should be removed (cleaned off) completely, in order to restore and conserve the sewing or the spine.
Several techniques are used for loosening and clean off old glue from spines.
Be careful when you clean off the animal glue from the book spine. Watch this video tutorial, demonstrate one of the most applied practice.
In this video methylcellulose solution with a concentration of 4% has been used (Viscosity: 2000 cPs at 2% in water, pH 7.0.)