Scrying comes from the Old English word "descry" meaning "make out dimly" or "reveal." By adding the prefix/suffix 'be', we get the modern word "describe".

Scrying has been used in many cultures as a means of seeing the past, present, or future; in this sense scrying constitutes a form of divination. It the occult practice of using a medium, most commonly a reflective surface or translucent body, to aid perceived psychic abilities such as clairvoyance. The media often used to "see" are crystal balls, water, polished precious stones or mirrors. Scrying, thus, uses a "visual" process. There are some who believe the art of scrying is not limited to the use of "reflective" or "translucent" bodies only, but includes other media.

The Ancient World
Scrying has been used for thousands of years by different cultures. Ancient Egypt used scrying in their Initiations including water scrying, dream scrying, oil scrying, and mirror scrying.

One legend states that the goddess Hathor carried a shield that could reflect back all things in their true light. From this shield she allegedly fashioned the first magic mirror to "see."

Ancient Greeks and Celts practiced scrying using crystal, black glass, polished quartz, water, and other transparent bodies.

Nostradamus allegedly used a small bowl of water as a scrying tool into which he gazed and received images of future events. Alchemists Edward Kelley and John Dee employed a form of scrying using a small crystal ball or shewstone, a piece of polished obsidion. Merlin was said to favor a crystal globe for scrying.

Although crystals may grow to a considerable length, they seldom exceed one inch in thickness. There are however some exceptions. Flaws in a crystal such as cracks, bubbles and discolorations do not make crystals unfit for scrying, although they may distract your attention.

Practical Application of Scrying
With respect to the medium used, size is not important and bigger does not mean it will work better.

Crystal scrying should be done in near or total darkness. The main thing is to avoid reflections on the surface of the crystal. The best method is to use the light of a candle when scrying but make sure the candle does not reflect in the ball.

Focus your gaze on the center of the crystal not on its surface. Try looking through the crystal as if it were a mirror upon the astral world.

The first thing you may see is clouds that change colour. Eventually a mist will spread outwards from the center of the crystal to reveal images.

When you scry for visions sooner or later you will achieve communication from the spirits. These spirits will help you to understand what you have seen in the visions.

It may be helpful to charge your crystal once a month with moonlight. Place the crystal in a glass bowl of natural water in the glow of a full moon.