paper with an uneven, corrugated surface, rather like exaggerated laid lines, but caused by passing the paper between ridged rollers. Viewing the stamp at an angle towards a light source will cause shadows to appear along the ribbing. The illustration to the right has been digitally enhanced to show off the horizontal ribbing. Some stamps, notably a few in the Wilding series, come either horizontal or vertical ribbed. Some ribbing may only show on one side of the stamp.