Pot metal is a widely used, inexpensive material whose properties, including whether it attracts a magnet, often cause confusion. This is because the term is not a precise metallurgical designation but a catch-all for various low-cost alloys. The magnetic behavior of any metal depends entirely on its internal atomic structure and the elements it contains.
Understanding Pot Metal Composition
Pot metal, sometimes called white metal or monkey metal, is a generic term for alloys characterized by a low melting point, making them ideal for fast, inexpensive casting processes. Historically, the name originated from manufacturers melting various non-ferrous scrap metals together in one “pot.” There is no single, standardized composition for pot metal.
The primary component of most modern pot metal alloys is zinc, which has a relatively low melting temperature of 786°F (420°C). This high zinc content is mixed with varying amounts of other low-melting-point metals like tin, lead, copper, aluminum, or magnesium. The exact proportions change depending on the manufacturer and the intended use.
Ferrous Metals and the Source of Magnetism
For a metal to be strongly magnetic, it must exhibit ferromagnetism, a rare characteristic primarily confined to three elements: iron, nickel, and cobalt. These metals possess a specific atomic structure with unpaired electrons that align their magnetic moments in the same direction, creating a strong attraction to a magnet.
The term “ferrous” describes metals that contain iron and are commonly magnetic. Conversely, “non-ferrous” metals, such as copper, aluminum, and zinc, do not contain significant amounts of iron and are inherently non-magnetic. Zinc, the main ingredient in pot metal, is classified as diamagnetic, meaning it is very weakly repelled by a magnetic field—an effect undetectable without specialized laboratory equipment.
The Magnetic Properties of Pot Metal
Pure pot metal, which is predominantly a zinc alloy, is not magnetic and will not stick to a household magnet. Since zinc is non-ferrous and lacks the atomic structure necessary for ferromagnetism, the resulting alloy remains non-magnetic.
The main source of confusion is that many objects made of pot metal do attract a magnet, but this is not due to the alloy itself. This magnetic attraction is typically caused by the inclusion of a separate, ferrous component within the finished product. Common pot metal castings, such as antique toys or die-cast hardware, often feature embedded steel screws, pins, or internal rods for added strength or functionality; these steel parts are highly magnetic.
Trace amounts of iron contamination from scrap metal used in production are usually too low to cause significant attraction. More commonly, the magnetic pull originates from a magnetic component beneath the non-magnetic pot metal shell. If a magnet sticks to a pot metal item, it is almost certainly attracted to an internal steel element rather than the alloy itself.