BRITISH COLOUR STANDARD - Mineral Blue Handmade Glass TumblerMade in an unusual blue tone, this beautiful hand blown glass tumbler is designed to deliver some colour. The colour Mineral Blue is taken from Blue John (also known as Derbyshire Spar) a semi precious mineral, a form of fluorite with bands of a purple blue. Lighter and finer, these tumblers are stackable. Every piece is hand made by skilled artisans and no two are exactly alike. Hundreds of tiny air bubbles in the glass create a light, bubbly effect