Writing is an age-old cultural technique. Thousands of years ago, humans were already carving signs and symbols into stone slabs. Scripts have become far more sophisticated since then but one aspect remains the same: Whether the writer is using cuneiform or a modern alphabet, a solid substrate, such as clay or paper, is required to fix the written structures in place.
Click here for original story, Writing in water using an ion-exchange bead as a pen
Source: Phys.org