Stained glass colored throughout its thickness is called pot-metal glass.
The name refers to colorants being mixed into the molten glass in the pot or furnace before the material is rolled or blown into sheets. Because the color runs through the entire piece, cutting or scratching the glass does not remove a thin colored surface layer.
Pot-metal glass contrasts with flashed glass. Flashed glass consists of a thin layer of colored glass fused onto a body of clear or differently colored glass. A maker can sometimes abrade or etch the flashed layer to reveal the glass beneath, which is useful for detailed designs.
The phrase “stained glass” can therefore describe several different constructions. Some pieces are colored in the batch, some have surface-applied enamels, and some combine multiple layers. Pot-metal glass is a material description, not the name of a window style or a joining technique.