what substances can be used as magnifiers?

Answer 1

Glass, quartz, clear plastic like acrylic...any clear substance in a double convex shape (not concave!) will work as a magnifier. The magnification ratio depends upon the curvature of the lens. The more curved, the shorter will be the focal length and greater will be the magnifying power.

Answer 2

anything that is clear and shaped in a concave shape. These shapes will bend the light creating a bigger image than the actual object, thereby magnifying it