The Romans used shiny objects and stones. Water has been used for gazing into. Mirrors are often used. There is an example of the interior of a cauldron being painted black, then filled with water at night, a silver coin was dropped into the water so to reflect moonlight. Such means have been employed to see visions and read mystical signs.
Many witches scry in a magic circle to prevent outside influences from distorting their visions.
Also, this is why most scrying is done at night in order to receive better psychic vibrations. As a general rule most diviners work at night in order to avoid the excessive psychic vibrations that are generated in the day due to the confusion of everyday living. The methods of scrying differ but after a period of concentration on the speculum visions, mental images, or impressions appear. Frequently the visions are symbolic and the scryer must be trained and skillful in interpreting their meanings.