Ferrography is Microscopic / Morphological analysis of Wear Metals in Oils where by operator use a Microscope to visually see the particles and identify the metals same based on color, structure. also this gives a approximate understanding on the type of wear in the machine.However Sprectrographic (spectroscopy)is using a spectrometer where by intensity of light is used to determine the element and counts / intensity the quantity.
Ferrography is subjective - qualitative in a way and Spectroscopy is quantitative.
both are goo tools for Relaibility.