Most printing today relies on ink, but there are many inkless options.

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In an increasingly paperless world, you'd guess printing would become obsolete. But that's not the case. Because reading computer screens strains people's eyes and they'd prefer to hold a book or newspaper in their hands, printing technology remains indispensible. Ink on the other hand, we could do without.

Let's face it -- ink is messy, expensive and high-maintenance. Wouldn't it be nice to eliminate it? Some old and new technologies provide the opportunity to do just that. Of course, whether a process is truly "inkless" depends on what your definition of "ink" is.

Generally, true ink consists of a dye or pigment, which can be organic or inorganic, in a liquid. A dye is a colored substance that dissolves in a liquid solvent, while a pigment consists of very fine, sometimes powdery, colored particles that don't dissolve, but rather are suspended in a liquid. The solvents and liquid that hold the dye or pigment can be water, or even oils or alcohols [source: Evans].

Many methods, both ancient and cutting edge, allow us to forego ink. The old methods of printing, such as engraving, don't involve anything like ink. Engraving uses a tool to imprint or carve words or images on a hard surface. However, as impressive as it looks on special plaques, engraving obviously can't be used on common paper, so it's an impractical, difficult and expensive process. Another inkless printing technique, hot foil printing, applies foil to a surface by applying heat and pressure. While the text looks attractive, this method is also impractical for mass production.

But newer technology is allowing us to print conveniently and cheaply without a drop of ink. What are these cutting-edge inkless printing methods? Keep reading to find out.