That is chemical analysis of metals from the spectrum of its components. Here is a sample in a spectrometer by means of arc spark test (also evaporate or burn in a flame is possible). That everything from the spark arc (or flame) sent light is split into its spectrum, so that the characteristic spectral lines of all elementary material components are visible.

These spectral lines are identified and there is the qualitative analysis of the individual elements contained in the sample. The light intensity of the spectral lines depends always on the mass content of the respective material components, thus can be performed in addition to the qualitative and quantitative analysis. Here, a certain characteristic spectral each of the elements in question with other spectral lines of different light intensity is compared.

From the measured intensities are calculated the concentrations in the unknown sample by comparing measurements with samples (reference-/calibration samples) of known element contents.

The most important thing for a successful measuring is a good sample preparation. To receive significant analysis results, a clean and plane grinded sample surface is essential. Outer pollution like rust or grease can cause falsifications of the results. Just a simple finger print at the surface of the sample to be analyzed can become noticeable. This example shows, how highly sensitive the instruments can react. A optimal sample preparation shows the video (SCHÜTZ+LICHT Prüftechnik GmbH).

Additional references:
GJS 
GJL 
GJV 
Sample taking 
Pig iron 
Sample grinding machine 
Remelting unit 
Electron probe micro analysis
Electron microscopy
X-ray
Element distribution