The short-lived [Harry] Bastow Glass Co., Coudersport, Pennsylvania (late 1903 to May, 1904) made a line called Pompeii which had ribs and frit. I've seen items in green glass with amber frit that look much like this shape, I think. A nice profile picture would really help, especially so I could see the contour near the bottom of the piece.
I don't think this is any sort of "baked on" enamel or a cold decoration. The white/blue colors and texture look much like Harry Northwood's "Granite Ware" from Ellwood City in 1894-95, and Bastow was there, learning all he could from Harry Northwood.