There are four known methods for sizing any ring - the first of which is simply using a ring stretcher, though this is rarely used as it makes the shank thinner and weakens the overall integrity of the ring. These courses of actions are not often endorsed or recommended by experts for these reasons.
The second method - much safer than the first - is used solely on plain wedding bands (those that have no stones in them) for both men and women: The ring is first placed in a cylindrical bowl that is a size smaller than the ring. Then, with a flat-shaped tool, pressure is applied to an area of the ring, which compresses it. No gold is added or lost in this process.
The third method, used for sizing rings up, involves cutting the bottom of the shank, pulling the two sides apart, building a bridge of new gold based on the size needed and then soldering it in - preserving the thickness at the base of the ring, where it is most essential. Usually, a laser is used to weld the extra bridge of gold - giving us the ability to size a ring quicker and more accurately than with the traditional style.
The last method, used for sizing rings down, is accomplished by cutting the bottom of the shank, taking out the proper length of gold and soldering the two pieces back together. A laser welder is used for the process as well, ensuring the most accurate sizing.
One concern that customers tend to have relates to the integrity of the side stones after a ring has been sized either up or down. The stones are always checked before sizing; if any of them are loose, they are tightened before continuing. This ensures that none of them will be compromised during and after the process.