The principles and development of ferrography, a method of particle analysis for fluids, especially wear particle analysis for oil-wetted machine components, will be explained. First, a brief review of the particles of wear, a knowledge of which allows prediction of incipient failure, will be presented, then a model (1)* to explain why wear particle concentration reaches equilibrium in the oil of any machine. Recently, ferrogram preparation materials have become available which allow deposition of non-magnetic organic particles for subsequent analysis which will also be discussed.
