To cut a long story short, it need not be a crystal ball, it started with frozen ice sphere found in river beds when the weather is very cold. The ice freezes around the debris and flows away first; overnight the ice crystal balls form and are very clear.
The ice ball is placed in a receptacle made of light metal (Aluminum) in a hole in the center of a table. Underneath is a basin attached to the table containing amber coal. This is how people keep warm in cold regions; they hide their legs under the table cloth; a fire place under the table.
In summary,
The crystal is a focusing device. The hollow aluminum holder and a temperature gradient, hot below, cold atop is the crux.
Compare this setup with Kozyrev's mirror of spiral aluminum partition, the ground on which the mirror is placed, is cold and the air on top of the mirror is warm. It is the opposite to the temperature gradient in the crystal ball set up above. Maybe, this is the reason why Kozyrev's mirrors are nauseating.
Which brings to mind,
one sees the future, the other looks into the past; left, right respectively. The focus however is not onto the eye, but on the forehead between the brows. Time energy is aimed into the pituitary gland, often called The Third Eye. Place the end of the telescope made of aluminum tube on the middle of the forehead.
To cut the story even shorter,
To be able to manipulate time flux, is true mastery over time.
Good grief.