Things You'll Need
Fine grit sandpaper
Ring resizing is a fairly common practice and is the most-used method to fit old rings to a new hand or to correct a sizing mistake. The ring-resizing process can be performed in a few different ways, and the method of choice often depends upon the complexity of the band. For a large sizing discrepancy, rings are made bigger by cutting open the band and adding extra material, which is a fairly involved process. For smaller changes on a simple band, however, ring band size can be increased with the use of a ring mandrel.
Slide the ring onto the ring mandrel and push it as far as you can down the length. Make note of the current ring size and how much it needs to be increased.
Take the mallet and tap the ring band gently on all sides, so that you are creating an even size change.
Push the ring farther down the mandrel, if possible.
Tap the ring band with the mallet again, hitting all its sides evenly. Check the sizing again by pushing the ring down the length of the ring mandrel.
Continue tapping and moving the ring band until you have achieved the desired size expansion. If necessary, give the ring band a brief sanding and polishing.
Resizing a ring on a mandrel will certainly make the ring band thinner. Make sure the ring you are working on is initially fairly thick. Thin bands may break or you may reduce the life of the ring significantly. Do not use this method of resizing if you need to expand the ring by more than half a size. Do not use this method of ring resizing on a ring that has stones, especially those fit with a tension setting, as you may damage the setting.