Sulphuric anodising, is formed by using an electrolytic solution of sulphuric acid at room temperature and a current density of 15 to 22 amps per square foot. The process will run for 30 to 60 minutes depending on the alloy used. This will produce a generally clear coating, depending on sealing, a minimum of 8cm thick.
There are hundreds of governmental, industrial and commercial anodising specifications in use, each with their own method of calling out coatings, seal, dyes etc.
Sulphuric anodising is rather tolerant to aluminium alloys with the exception of high-silicon die-cast alloys. The less alloying elements there are the higher clarity and depth of colour of the anodise coating.
Sulphuric anodising provides for several desirable qualities such as:
Sulphuric anodising coatings are often sealed to enhance corrosion resistance, lock in dyes, or both. Hot water seals produce the clearest sulphuric anodise while sodium dichromate yields a yellow/green appearance but generally a better seal.