ISO 4630-2:2004 specifies a method for estimating, by means of the Gardner colour scale, the colour of clear, yellow/brown liquid products using colour-measuring instruments. The results may be invalid if other products are tested. The test uses the Gardner colour scale described in ISO 4630-1, which describes a visual method. The method is applicable to drying oils, varnishes and solutions of fatty acids, polymerized fatty acids, resins, tall oil, tall oil fatty acids, rosin and related products. The method described provides a more precise way of measuring Gardner colour than that described in ISO 4630-1. It is applicable to products having colours from Gardner 1 to Gardner 18. The Gardner scale is not applicable to products with colours lighter than 1 or darker than 18.