18ct White Gold Blue John 0.53 Carat Diamond Cushion Top Ring. R897. This enchanting ring boasts a striking cushion shaped piece of rare Blue John stone that has been directly sourced from Treak Cliff Cavern in Castleton. The stone is set within exquisite 18ct white gold and surrounded by a sparkling array of 0.53ct brilliant cut diamonds that frame the Blue John stone and run down the split shoulders, finishing in a classic band. All our Blue John jewellery is designed and crafted within our very own workshops in Ashbourne, Derbyshire where a team of skilled craftsmen turn the raw Blue John stone into these stunning pieces of jewellery. You can find other matching Blue John jewellery and other Blue John rings on our website. 18ct White Gold Blue John 0.53 Carat Diamond Cushion Top Ring.