All fused glass will have a shiny side on the side that’s “up” in the kiln. The down side, against the kiln shelf, will pick up the “texture” that it is fired against. Fiber paper helps a lot in making a smooth bottom, and the kind that is disposable after only one firing (use your respirator – it’s toxic after firing!!) seems to have the smoothest surfact.
Hope that’s helpful,
Windows listen attentively for the sound of broken glass.