ISO/TR 15922:2011描述了评估铬酸盐转化涂层卷材和板材产品中观察到的暗斑现象特性的方法。 含有三价或六价铬离子的铬酸盐转化涂层应用于热浸金属锌和电镀锌钢产品，以增强部件的耐腐蚀性。 在高温和高相对湿度下长期储存后，如果打开带有转化涂层的镀锌包装卷材和板材产品的包装，板材产品的表面会出现污点。当使用这些受影响的板材生产零件时，这种变色表现为深色或黑色污渍，并影响外观和耐腐蚀性。

ISO/TR 15922:2011 describes the methods to evaluate the properties of dark-stain phenomenon observed in chromate conversion-coated coiled and sheet products. Chromate conversion coatings, with trivalent or hexavalent chromium ions, are applied to hot-dip metallic zinc and electroplated-zinc steel products to enhance corrosion resistance of the components. When zinc-coated packed coiled and sheet products with conversion coatings are unpacked after long-term storage at elevated temperature and high relative humidity, the surface of the sheet products appears tarnished. This discolouration appears as dark or black stain and influences the appearance and corrosion resistance, when parts are produced using these affected sheets.