MEK

Methyl-Ethyl Ketone, sold under the brand name "Ambroid Pro-Weld" and others. MEK works by actually melting the plastic being worked, making the kit builder easy to identify (see JMN) as the runoff from application invariably heads for a finger and permanently etches a fingerprint in the model. Evaporates absurdly quickly if left open -- considered by many to be a conspiracy by hobby shop owners.