Does the diamond come with a certificate for insurance purposes?
Usually, a single diamond over 0.30ct in weight will come with an independent diamond certificate.
Uncertified diamonds are available - and can offer a more cost effective alternative to certified stones as you are not being on-charged for the certification process.
For insurance purposes you will need to get the finished jewellery assessed by an independent registered valuer and they will probably need to see the diamond certificate with the jewellery. They will test and verify all the materials that the ring is made of and estimate the value of the ring for insurance purposes.