A pen is a common writing instrument used to apply ink to a surface, usually paper, for writing or drawing. Historically, reed pens, quill pens, and dip pens were used, with a nib dipped in ink. Ruling pens allow precise adjustment of line width, and still find a few specialized uses, but technical pens such as the Rapidograph are more commonly used. Modern types include ballpoint, rollerball, fountain and felt or ceramic tip pens.
The main modern types of pens can be categorized by the kind of writing tip or point on the pen:
- A ballpoint pen dispenses an oil-based ink by rolling a small hard sphere, usually 0.5–1.2 mm and made of brass, steel, or tungsten carbide. The ink dries almost immediately on contact with paper. The ballpoint pen is usually reliable and comes in both inexpensive and expensive types. It has replaced the fountain pen as the most common tool for everyday writing. (There are certain ballpoint pens combining multiple colours in a single barrel; the writer or artist may depress the tip with the desired colour.)
- A rollerball pen dispenses a water-based liquid or gel ink through a ball tip similar to that of a ballpoint pen. The less-viscous ink is more easily absorbed by paper than oil-based ink, and the pen moves more easily across a writing surface. The rollerball pen was initially designed to combine the convenience of a ballpoint pen with the smooth “wet ink” effect of a fountain pen. Gel inks are available in a range of colors, including metallic paint colors, glitter effects, neon, blurred effects, saturated colors, pastel tones, vibrant shades, shady colors, invisible ink, see-through effect, shiny colors, and glow-in-the-dark effects. Refillable rollerball pens have recently become available using cartridges of fountain pen ink.
- A fountain pen uses water-based liquid ink delivered through a nib. The ink flows from a reservoir through a “feed” to the nib, then through the nib, due to capillary action and gravity. The nib has no moving parts and delivers ink through a thin slit to the writing surface. A fountain pen reservoir can be refillable or disposable; the disposable type is called an ink cartridge. A pen with a refillable reservoir may have a mechanism, such as a piston, to draw ink from a bottle through the nib, or it may require refilling with an eyedropper. Refill reservoirs, also known as cartridge converters, are available for some pens which use disposable cartridges. A fountain pen can be used with permanent or non-permanent inks.
- A felt-tip pen, or marker, has a porous tip of fibrous material. The smallest, finest-tipped felt-tip pens are used for writing on paper. Medium-tipped felt-tips are often used by children for coloring and drawing. Larger types, often called “markers”, are used for writing in larger sizes, often on other surfaces such as corrugated boxes, whiteboards and for chalkboards, often called “liquid chalk” or “chalkboard markers”. Markers with wide tips and bright but transparent ink, called highlighters, are used to highlight text that has already been written or printed. Pens designed for children or for temporary writing (as with a whiteboard or overhead projector) typically use non-permanent inks. Large markers used to label shipping cases or other packages are usually permanent markers.
- A gel pen uses ink in which pigment is suspended in a water-based gel. Because the ink is thick and opaque, it shows up more clearly on dark or slick surfaces than the typical inks used in ballpoint or felt tip pens. Gel pens can be used for many types of writing and illustration. Gel pens often come in bright or neon colors.
- A stylus pen, plural styli or styluses, is a writing utensil or a small tool for some other form of marking or shaping, for example, in pottery. It can also be a computer accessory that is used to assist in navigating or providing more precision when using touchscreens. It usually refers to a narrow elongated staff, similar to a modern ballpoint pen. Pens exist which contain a ballpoint tip on one end and this sort of touchscreen stylus on the other.