Abstract: A process of determining the type of a diamond of unknown type, said process including the steps of (i) applying a laser input signal to a diamond of unknown type such the NV? centres or other C centres such that fluorescence is generated from said diamond; (ii) applying a magnetic field to said diamond and applying a variable microwave frequency to said diamond; (iii) acquiring the light intensity of fluorescence as a function of microwave frequency; and (iv) determining the type of the unknown diamond by comparing the light intensity of fluorescence as a function of microwave frequency of (iii) with light intensity versus microwave frequency characteristics diamond of known of a plurality of diamonds known types.