Introduction and Basic Overview

The flame will visually impart colours when selected elements such as sodium (yellow), potassium (blue) and calcium (predominantly red with a little green and blue) 

A Practical Approach to Quantitative Metal Analysis of Organic Matrices Martin Brennan 2008 John Wiley Sons, Ltd 

German physicist Joseph von Fraunhofer (1787-1826) discovered dark lines [1] and with the advent of more sophisticated optics he was able to attribute these lines (bands) to characteristic wavelengths. An early practical example of this is the separation and identification of lithium (Li) and strontium (Sr) in solution. In the Li and Sr example, one line or band is the wavelength for Li and the other for Sr. However, it is worth noting here that Li+ emits only one waveband while Sr emits several and despite this they are still identifiable for each element. Elements giving multiple colours (as calcium, above) illustrated the presence of several lines associated with a particular element. Kirchhoff and Fraunhofer were the first to observe these lines that are now assigned to wavelengths in modern spectroscopy. 

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