Googled it, and this is the result :
It seems they use "collodial silver"
"it is well known that the ancient Greeks knew the medical value of silver. It was observed that those ancient families who ate from silver utensils rarely were sick and had few infections. This knowledge passed on to kings, emperors, sultans and their families and members of their royal courts. They ate from silver plates, drank from silver cups, used silver utensils and stored their food in silver containers. As a result of this use, silver was ever so slightly rubbed off and mixed in their foods. And after a generation or two, they received the full benefit from the silver particles which found their way into the body of these people, hence had little chance of getting any infectious illness.
These royals were called Blue Bloods because their skin had a blue tint, due to the accumulation of minute traces of pure metallic silver. The common red blooded folk, however, ate from earthenware dishes with iron utensils and frequently were sick, whilst the royals enjoyed the freedom from infectious disease as early as from birth"