The nitric acid test is not suitable for gold coatings less than 0,6 micrometres thick, for coatings less noble than gold or platinum , or for gold-flashed palladium and its alloys
BS ISO 14647:2000 history
2000BS ISO 14647:2000 Metallic coatings - Determination of porosity on gold coatings on metallic substrates - Nitric acid vapour test