False. Opals are made up of hydrated silica – which are water molecules. Exposing your solid opal to moisture is absolutely fine and they can be washed in tepid (body temperature warm) water. As with other precious gems, exposure to water is not the issue – it is the dishwashing detergent and other chemicals that may be in the water that may damage your opal. It is always best to take your opals off before handling food or other chemicals.