The glassworkers of northern Italy used the robustness of the iron blow-pipe to particularly good effect during the second quarter of the 1st century A.D. to produce a range of small, colorful bowls with a distinctive pinched-rib finish. Some glass of the ground colorusually amber or purplewas gathered up while hot, and several threads of white glass were wound about it. Reheating this mass softened it sufficiently so that, as it was rolled on a flat wooden slab, the white glass was pressed flush (marvered) into the surface. This two-color gather was then blown into a globular shape, its lower side-wall modified with square-nosed pliers and its upper body cut to form the bowl's rim.
A similar technique also was used to create polychrome two-handled jars and bottles, except that the initial gather was partially blown before it was rolled in a heap of colored glass chips. Subsequent marvering then smeared out the decorative colors and completion of the blowing process stretched those colors into a host of flowing patterns. The pinched-rib bowls were exported the length and breadth of the Empire, whereas polychrome vessels only found favor in the western provinces.