ISO 8502-3:2017 describes a method for the assessment of dust remaining on cleaned steel surfaces prepared for painting. It provides pictorial ratings for the assessment of the average quantity of dust. It also provides descriptive classes for the assessment of the average size of the dust particles. The method described is a qualitative test useful for a steel surface, before cleaning, corresponding to rust grade A, B or C as defined in ISO 8501-1. It can be used as a "pass/fail" test or to provide a permanent record of the dust present on a surface.NOTE The quantity ratings and size classes referred to in this part of ISO 8502 are derived from ISO 4628-1.