Performing a flame test (yellow) on barium. A flame test is a simple way to test for the presence of certain metals in a compound. A small amount of the sample is held on a platinum wire in a Bunsen flame. Some metals can be detected by the colour of flame produced. The colour of the flame is caused by the fluorescence of the metal ions within it; the compound is ionised by the heat and the excited metal ions give out light of a characteristic wavelength or colour. Platinum wire is used as it does not give a flame test colour of its own.