Uranium is/was used in glass as a colorant. On it's own it produces a bright lemony/lime green colour, which is greatly enhanced in daylight (i.e., by the UV in sunlight). With other colorants it gives a richness to many variations of green glass, but quite why it was used in some blue and amber glass I have no idea. In Murano glass, it seems to have been used mainly as a colorant for clear glass either as an outer layer or below a clear upper layer, as far my observations go