Alabastron
Greek core-formed alabastron of opaque, milky-blue glass with a flaring rim. To create this piece, a core of organic and inorganic materials in the shape of the vessel's interior would have been formed on the end of a rod and then dipped into a gather of blue molten glass. The core materials would then have been removed from the interior of the vessel as part of the finishing of the piece.
Images courtesy of The Metropolitan Museum of Art (CC0)