It is a decorative piece what can have a function as underground for, by example, a thee set. The glass is as normal glass, the colors variate from dark yellow till dark red/brune. Slag glass is thicker as I see on the internet. This is more real glass. The descripe worked means carved for decorations. I don’t know the origin, maybe it is England. I’m from the Dutch, but don’t think it’s Dutch.
Today I will make a better pricture what shows the glass type (hope).