A magnetic stirrer, or stir plate, produces a rotating magnetic field that causes a magnetic stir bar to spin, mixing liquids within containers placed on or over the stirrer's platform. Stirring bars are included with some stir plates. Also known as a magnetic mixer, a magnetic stir plate is generally more efficient and easier to clean than a motorized mixer. It has no external moving parts and the stir bars are the only parts in contact with the liquid being mixed.
Among the factors to consider when selecting a stir plate are the platform size and material, speed range, and stirring capacity. Platforms, or plates, may be sized to hold one or more lab containers, and may be made of materials such as ceramic, aluminum, porcelain- or powder-coated stainless steel, and plastic. The speed range and stirring capacity varies from model to model. Units are available with top speeds of more than 2,000 rpm. While stir plates typically have a capacity of several liters or less, large volume stirrers used in pilot plants or as part of process equipment in manufacturing can have a capacity of 200L or more.
Some stir plates have a temperature control so they can also function as a hot plate and these units often have an indicator that signals when the plate exceeds a certain temperature. Other features may include a digital display, a timer for setting the duration of operation, an onboard memory for storing user-defined stirring functions, an output for transmitting data to a computer, and an integral ring stand holder. Certain units meet International Organization for Standardization (ISO) 9001 standards or are Ingress Protection (IP) rated against dust and water. There are immersible models that can be placed into water baths. A magnetic stirrer is used in a variety of applications such as laboratory research, paper making, brewing, and even calligraphy for mixing metallic inks.