As I mentioned, for me in started with the airplane when our mechanic recommended that the oil and filters from the gas turbine engines be sent to lab for testing periodically. You have to send in the filters because they are typically 10 micron and don't leave much in the oil for them to test what might be wearing or breaking down. The reports tell you about the life of the oil, debris found in the oil, size, and probable source, detergent capability, contaminants found (for autos this would include coolant, fuel, additives, etc.
From there, I started sending oil from cars in for testing, using primarily Blackstone Labs, with the additional particul analysis. The lab measured the results, and they provide you with a detailed analysis of what your oil is doing compared to their extensive database, and they give recommendations. The particle analysis tells you right away if what size the filter is removing particles down to.
The SAE has published a couple of articles that correlate the size of debris in vehicle engines with excessive wear, and IIRC they were bigoing on trapping everything above 20 to 25 microns.
Travis