The 1 mm [0.039] thick aluminium plate is bent over a cone – one end has a small radius, and the other has a large radius. The smaller the radius, the more potent effect on the paint and consequently it will crack, meaning that the metal will become visible. For a positive result, the paint should not crack where the radius exceeds 2.25 mm [0.088]. (The test is per the following standards: DS/ISO 2408, 1976).