A fountain pen contains an internal reservoir of water-based ink that draws the ink to the nib through a combination of gravity and capillary action. The earliest known record of a similar writing utensil, which did not constantly leak or require pressure, is from documents written in the 10th century about a North African caliph. More modern references to pens with ink reservoirs have also been traced to 17th and 18th century Europe when the term "fountain pen" started to be used. In 1830, stainless steel pen nibs began to be mass produced, allowing pens to be more accessible and encouraging literacy. Gold alloys and iridium (of the Platinum metal group) were also commonly used in nib-making as they resisted corrosion and wear. By the 1940s and 1950s, fountain pens were the most widely used type of pen as ballpoints were expensive and inconsistent. Esterbrook was a major manufacturer as they offered interchangeable steel nibs at a reasonable price. Though beloved by artists and students, Esterbrook met its demise with the advent of the inexpensive ball pens.