A gemstone has to be set in such a way that it lasts - of course! That's the most important. The metal of the setting is carefully hammered over the stone in microscopically small steps. Be very careful - because the tool must not touch the stone. But there are a few other criteria to consider, for example that the setting covers as little of the stone as possible, or that the ends of the settings are rounded so that the ring does not get caught on anything.