text: The chemical composition of slag can reveal much about the smelting process. XRF is the most commonly used tool in analysing the chemical composition of slag. Through chemical analysis, the composition of the charge, the firing temperature, the gas atmosphere and the reaction kinetics can be determined.
  Ancient slag composition is usually a quaternary eutectic system CaO-SiO-FeO-AlO simplified to CaO-SiO-FeO, giving a low and uniform melting point.  In some circumstances, the eutectic system was created according to the proportion of silicates to metal oxides in the gangue, together with the type of ore and the furnace lining. In other instances, a flux was required to achieve the correct system.
  The melting temperature of slag can be determined by plotting its chemical composition in a ternary plot.
  The viscosity of slag can be calculated through its chemical composition with equation:
  where  is the index of viscosity.
  With recent advances in rotational viscometry techniques, viscosities of iron oxide slags are also widely undertaken. Coupled with phase equilibria studies, these analysis provide a better understanding of physico-chemical behaviour of slags at high temperatures.
  In the early stages of smelting, the separation between melting metal and slag is not complete. Hence, the main, minor and trace elements of metal in the slag can be indicators of the type of ore used in the smelting process.