This part of ISO 4628 describes a method for assessing the degree of blistering of coatings by comparison with pictorial standards. The pictorial standards provided in this part of ISO 4628 illustrate blisters in the sizes 2, 3, 4 and 5, and each size in the quantities (densities) 2, 3, 4 and 5. ISO 4628-1 defines the system used for designating the quantity and size of defects and the intensity of changes in appearance of coatings and outlines the general principles of the system. This system is intended to be used, in particular, for defects caused by ageing and weathering, and for uniform changes such as colour changes, for example yellowing.