By anodising the aluminum, a lattice of pores form and these must be closed for the product to obtain optimal compression, weather-resistance, and aesthetical appearance.
The sealing process “seals up” the surface by creating Böhmite crystals, so water is chemically bound in the anodising layer.
When sealing, the pores in the surface absorb the water so they are sealed off, and the surface itself is now sealed.
The process takes place in 98°C hot water, where the water becomes chemically bound to the anodising layer by creating Böhmite crystals. Sealing in water is a standard procedure when anodising, which can be deselected – for instance, if paint or adhesive will be applied to the surface.
To maximise the protection for corrosion, anodised products can be dichromate sealed. Dichromate sealing is a chemical chrome compound which also seals the built-up anodising layer. During this process, chrome is absorbed by the surface.
Normally this process is not used for decorative purposes as the surface becomes dark green – and it is not possible to dye the product afterward.