A glass article such as a sham bottom tumbler with a decorative air bubble encapsulated in its base is produced on existing automatic glass-forming machines by injecting a bubble of air into a charge of molten glass in the gob-feeder section of a glass furnace as the charge is being formed into a gob. This is accomplished by mounting an air supply pipe in the gob-feeder orifice. Preferably, the outlet end of the pipe extends radially to the center of the orifice. Puffs of compressed air are supplied in synchronism with the feeder plunger cycle so an air bubble is formed in the lower end of the gob, and the gob is then formed by normal procedures into a finished article.