How is Sulphuric Acid Anodizing different from other types of anodizing?

It is particularly suited for applications where hardness and resistance to abrasion is required. However, where parts are subjected to considerable stress, (such as aircraft parts), the possible presence of the corrosive acid residue is undesirable. The porous nature of sulphuric acid films prior to sealing is used to particular advantage in the production of coloured surface finishes on aluminium and its alloys. The porous aluminium oxide absorbs dyes well, and subsequent sealing helps to prevent colour loss in service. Although dyed anodized films are reasonably colourfast, they have a tendency to bleach under prolonged direct sunlight. Some of the colours are: Black, Red, Blue, Green, Urban Grey, Coyote Brown, and Gold. Parts can be treated chemically or mechanically prior to anodizing to achieve a matte (non-reflective) finish.