English: Demonstration of flame colors used in the flame test by heating potassium chloride in a Bunsen burner flame. Excitation of electrons causes release of electromagnetic radiation whose wavelengths are element-specific. In some cases, these wavelengths fall into the visible spectrum, making them useful as a test for certain elements, in this case potassium. The lilac flame color of potassium is often obscured by tiny amounts of sodium impurities which color the flame a bright yellow. The potassium flame is visible through a piece of blue cobalt glass which filters out the yellow light.