Many vessels are simple, but around half contain designs of some type, most often lines and waves produced by impressing a string onto wet clay before the fire, thus the term Jomon or rope design for the ceramics and time frame of this era of Japanese culture. Scholars distinguish between Chinsen-mon in the east of Japan, where seashells were used to perforate the clay, and Oshigata-mon in the western area, where imprints were formed with a dowel. Toward the conclusion of the era, decoration is reduced and, in some areas, vanishes entirely.