Hi. Can some help with this pair of slag glass tumblers. Found in the North West of England. They measure 4.5 inches (11.5 cms) high x 2.7 inches (6.5 cms) in diameter at the widest part (rim). Colours are shade of purple & whites. Quite heavy each one weighs almost 200 grammes. I think there is a makers mark on the base - possibly a Y. I've attached photos so if anyone can help it would be much appreciated