Sapphires are on the whole, very durable stones and are safe to use in jewellery dips and ultra-sonic cleaners, however avoid using heat with untreated stones as this could affect the colour and future recertification. Avoid coating with borax before applying heat as borax may eat into sapphires.
More care is needed with treated stones.
Sapphires can be treated to improve colour by a process called diffusion. Older stones treated in this way may only have treatment near the surface, so if you become aware that you or a customer has a stone treated in this way avoid repolishing.