Tungsten (element W, atomic number 74) is a refractory metal known for its immense robustness. It possesses the highest melting point of all known elements at 3,422°C. Tungsten is also one of the densest metals, comparable to gold (19.3 g/cm³). Pure tungsten is a silvery-white or grayish metal.
The Characteristic Color of Tungsten
Pure, unoxidized tungsten at room temperature exhibits a bright, metallic luster. Its inherent color is best described as silvery-white, sometimes possessing a subtle gray undertone. This appearance is characteristic of many transition metals, reflecting light across the visible spectrum.
The metal can be polished to achieve a mirror-like finish, maximizing its reflectivity. However, tungsten’s overall brilliance is slightly less than that of highly reflective metals like silver. When compared side-by-side with pure silver, tungsten often presents as a more steel-gray hue.
How Surface Conditions Affect Appearance
The color of tungsten can change significantly based on its surface condition and environment. A highly polished sample displays the maximum reflective, silvery-white color. In contrast, typical industrial samples or those exposed to air may appear duller or distinctly colored due to surface films.
Tungsten is susceptible to oxidation, or tarnishing, when exposed to air, especially at elevated temperatures or with moisture. This process forms a thin layer of tungsten oxide on the surface. The most stable oxide, tungsten trioxide (WO3), is a distinct yellow crystalline solid.
The thickness of the oxide layer determines the resulting color through a phenomenon called thin-film interference. Before the entire surface turns to the bulk yellow oxide, the thin film can produce iridescent effects. This can cause the metal to display colors like gold, blue, or purple.
The Color of Incandescence
The most common public perception of tungsten’s color is the light it emits when heated, not its reflective metallic shade. Due to its high melting point, tungsten is the material of choice for filaments in incandescent light bulbs. In this application, the metal is heated to extreme temperatures, typically ranging from 2,000°C to 3,000°C.
At these temperatures, the tungsten filament begins to glow brightly, a phenomenon known as incandescence. This glowing metal emits light in a continuous spectrum, which is a form of black-body radiation. The color of this emitted light is a warm, yellowish-white.
The characteristic color temperature of a tungsten filament lamp is often around 3200 Kelvin, giving it a golden hue perceived as “warm light.” This emitted light must be distinguished from the reflective color of the solid metal, which remains silvery-white until it is heated to the point of glowing.