Sealing wax is a material which, after melting, quickly harens (to paper, parchment, ribbons and wire, and other material) forming a bond that cannot be separated without noticeable tampering. Wax is used to verify something such as a document is unopened, to verify the sender's identity, for example with a signet ring, and as decoration. Sealing wax can be used to take impressions of other seals. It can be used to create a hermetic seal on containers. Wax was used to seal "letters close" and later (from about the 16th century) envelopes. (Before sealing wax, the Romans used bitumen for this purpose.)