Fig. 2
Composition of the microscopic substrate. MP particles imaged in reflected DIC mode appeared bright on dark background, however the contrast depended on the presence and direction of topographical features in the range of the polarised beam shear. Boundary creeping effects can lead to deviations or defects in the epoxy layer around particles, which may scatter light and become visual obstacles for image analysis: (a) sloping due to attraction to particle, (b) pit formation (depressions which become visible when particles would be destroyed). Normal smooth layer surface (c) typically found in inter-particle space shows no optical interference and provides an evenly dark background. Drawing not to scale