What is particle count?
Particle counting reports how many particles of each size range remain on a cleaned component, rather than just their total mass. Specifications are written as size-class limits — for example, no particles above 600 µm — because one large hard particle can fail an assembly that a gram of fine dust would not.
After the extraction wash used for a Millipore test, the membrane is scanned optically and particles are binned by their largest dimension. Modern systems also classify them as metallic, non-metallic or fibre, which is diagnostically useful: metallic swarf points at machining, fibres at wipes and packaging.
This distinction is why gravimetric mass alone is an incomplete specification. A part can pass on mass and fail catastrophically in service because of a single hard particle lodged where it will score a bore or block an orifice.
Chasing a particle-count spec usually means attacking sources rather than increasing wash time: finer bath filtration, better drag-out control, cleaner baskets, and packaging that does not shed.
