Glass and ceramic stove tops, though shiny and appealing, require more careful use than coil tops. Dragging canning equipment and cast-iron skillets over the cooktop can scratch the surface. In a worse-case scenario you may damage the heating elements or break the stove top. Although some say it's OK to use cast iron on a glass-top stove, it's a risky venture.
Cast iron is a heavy product, and a pot full of water or soup puts substantial weight on the glass cooktop. A slip of the hand while lifting a cast-iron pot may crack the top, making the stove unsafe and unusable. Manufacturers suggest removing heavy items from shelves over the cooktop to avoid damage from falling objects, as well. Whirlpool, a manufacturers of these stove tops, does not rule out the use of cast iron pots on a glass or ceramic cooktop but suggests that you use caution.
Pots and pans with flat bottoms are essential for even heat distribution on glass and ceramic stove tops, and most cast-iron cookware isn't perfectly flat. Nonflat cookware increases cooking time by 30 percent, reports the Utah State University Extension Service.
The recommended pot size is no more than an inch larger than the burner. Many cast-iron pots are much larger than the burners on your glass-top stove. If the pot is larger than the recommended size, the heat distribution is uneven. The element cycles on and off, reducing the cooking speed and the life of the element, according to Utah State University Extension Service. A large heavy pot like cast iron traps heat under the cookware. This heat buildup shortens the life of the element or may damage the cooktop surface.
Cast iron has a rough finish that can scratch the surface of a glass cooktop. Cast iron with enameling on the bottom is equally unsafe on the glass-top stove. If the pot overheats, the enamel may fuse to the stove top. Stainless steel is the metal of choice for ceramic or glass cooktops. Aluminum is usable but may leave gray marks on the surface.