Since the visual appearance of finished products is of high importance in terms of both aesthetic and functionality points of view, surface of the aluminum coil to be does have to have a high degree of clean lines and purity. Thus, existence of oxides, segregations, holes, stains, water stains, oil stains, scratches, bubbles, roll marks, chatter marks, orange peeling, color differences or any kind of impurity is not accepted. Incidents like grain growth or appearance difference etc. On surface are not tolerable in case they adversely affect the visual quality of finished product. Surface must be uniform.
Surface dirtiness, which is composed of both organic and inorganic (oil, smudge, oxide etc.) constituents, shall not go beyond 20 mg/m2 (sum of both surfaces). Measurement of dirtiness is carried out by weighing a sample with a certain surface area before and after cleaning with an appropriate solvent. Scale to be used shall have a precision of 0,1 mg at least. Difference of before and after weighings is divided by the surface area of the specimen to obtain dirtiness level.