A cachet is basically a rubber stamp. It is NOT a postmark. Postmarks can only be applied by official Post Offices where as anyone can design a cachet and put it on their cover. A cachet makes a cover unique and tells its story. It might show that the cover has been carried – for example this cachet on our Concorde cover shows that it was flown on the very last flight of Concorde.
Alternatively, a cachet could be used to give information about a signer or a postmark.
[First woman in Space] A good example is this cover signed by the first woman in space. A superb signature but not very readable and of course, if people don’t know who has signed, they don’t understand the value of the cover. In this case, the cachet gives information about the autograph.
[Hornby Cover] [QE2 Cover] As Royal Mail no longer counts pre-decimal stamps as valid and will not postmark them, you will often see cachets used to cancel any old stamps on a cover in the manner of a postmark. In the same way, it might be used to cancel a Cinderella stamp. The cachet is the link that touches both the stamp and the envelope and ties them together. For example, this Hornby coverhas a Hornby Cinderella, cancelled by a Hornby cachet while this QE2 cover is a prime example of cachets at their best! Details like cachets are what make a cover really special so they are worth looking out for.