Sealing wax is a wax material of a seal which, after melting, hardens quickly (to paper, parchment, ribbons and wire, and other material), forming a bond that is difficult to break without noticeable tampering. Wax is used to verify that something such as a document is unopened, to verify the sender's identity (for example with a seal stamp or signet ring), and as decoration. Sealing wax can also be used to take impressions of other seals. Wax was used to seal letters close and later, from about the 16th century, envelopes. Long before sealing wax was employed, the Romans used bitumen for this purpose.