Hi Sue, glass with a hint of opalescent fire as you refer to it. The pontil mark is simply a flat ground bottom. In reality the piece is likely mold blown and cut from the top. ground and polished rim, and merely ground flat and polished on the underside to make it stand up.
By cabinet vase I am referring to an example which is much too small to actually use as a vase, and were commonly stored in cabinets. Even small flowers and water would make this example quite unstable.
I would date the piece to early 20th, or late 19th century.