A method of spectroscopic analysis of a diamond for determining whether the diamond has been artificially treated to change its colour may include: generating light emission from a diamond upon optical excitation at a wavelength equal to or smaller than 680 nm; optically producing a dispersed light emission; detecting the dispersed light emission across a collected spectral region including emission wavelengths of from 670 nm to 735 nm; processing the output signals to produce a spectral intensity distribution as a function of emission wavelengths; analysing the spectral intensity distribution to determine the presence or absence of a spectral pattern including either an intensity peak at 681 nm or a combination of intensity peaks at respective wavelengths 705 nm and 725 nm; if a spectral pattern is present, establishing that the diamond has been treated; and if a spectral pattern is absent, establishing that the diamond has not been treated.