My favorite adhesive!

E6000 is a tough, flexible and highly versatile rubber-based compound that exhibits exceptional adhesive, contact adhesive and sealant qualities. -Eclectic Products, Inc., E6000 manufacturer

It is also clear, industrial strength, self-leveling, waterproof, paintable, and safe for photographs! The only ingredient listed is perchloroethylene, but the package does state it contains an unnamed chemical known to the state of California to cause cancer. Deliberate misuse may be harmful, as may inhalation or ingestion.

Highly superior to rubber cement, Elmer's, or any normal glue, E6000 can stick just about anything to anything. Permanently.