Cobalt rings has the premium white color which matches most white gold and platinum jewelry. We use the same cobalt chrome superalloy that is used in making jet engine and artificial joints it is bio-compatible and extremely durable. Because it is bio-compatible it is also hypoallergenic and will not cause any allergic reaction on any skin types. All our cobalt chrome rings are made true to size according to the U.S. ring scale and they all have the comfort fit design. Please note that cobalt rings are not resizable due to the extremely high melting point. Cobalt chrome has a very high tensile strength so titanium rings are very hard to be bent like gold or silver rings and they will always retain the perfectly round shape it will never shatter upon impact. Since our cobalt rings are made from solid cobalt chrome without any plating they will never change color or turn your fingers green they really do last forever.