The oldest known examples were created by incising a flat surface with a rigid tool rather than applying pigment with a secondary object, e.g., Chinese jiaguwen carved into turtle shells.The ancient Sumerians and their successor cultures, such as the Babylonians, produced their cuneiform writing by pressing a triangular stylus into soft clay tablets, creating characteristic wedge-shaped marks.The original form of "lead pencil" was the leaden stylus used by the ancient Romans, who also used it to write on wood or papyrus by leaving dark streaks where the soft metal rubbed off onto the surface.Initially, pens were made by slicing a suitable nib point from the end of a thin, hollow natural material which could retain a small reservoir of ink by capillary action.Quill pens were standard in Europe and the United States up through the 18th and 19th centuries, and are still used in various contexts, such as calligraphy and formal settings such as major bank transactions.Depending on the design of the pen, the ink reservoir can be filled in several different ways: direct addition by eyedropper, suction from an internal mechanism, or disposable pre-filled cartridges.This makes them particularly useful for fine diagrams or small handwriting, although different sizes of refill leads cannot be interchanged in the same pencil unless it has been specially designed for that purpose.The bristles are gently swept across the paper with just enough pressure to allow ink to wick onto the surface, rather than mashing down the brush to the extent of substantial friction resistance.Although pens with semi-flexible nibs and liquid ink can also vary their stroke width depending on the degree of applied pressure, their variation range is far less obvious.