Here at CM Weldon we use tried and tested techniques for sizing our rings here at the workshop. When you buy an engagement ring you more than likely have to have it sized. you can see in this video the use of more modern laser machine for accuracy as the ring is adjusted to perfection. To size a ring up, a little piece of metal is usually added after the back of the ring is heated almost to melting point allowing the bench jeweller to insert the piece and then solder it back into place. After that the ring is filed down and polished so that any trace of the sizing is virtually undetectable.