Try shining a black light (they make LED black flashlights now - lights are purple) on it, at some point, you won't see the purple of the light, you will see the glass kind of change color and become sort of creamy and shiny.
This is called amberina glass. It's yellow glass and the red part is held in the "glory hole" of the furnace for extra time, and it turns red. It has to have some gold in the glass to do that (in the old days) so it was extra expensive. I have a great collection of Amberina, just LOVE it. Someone will love this piece!