[Nasher]

Looking good Mr G

Not sure if I'm confused about exactly what process you've had done.

I Know the Blackening process for Mild steel as Chemical Blackening.
But it's often called Black Anodising as it's a process of converting a thin surface layer on the outside of the steel part to an Oxide, then the Black is created by dipping the part into hot Oil, which not only colours the part by seeping into the porous oxide layer, but seals it and hardens it.

Anodising Aluminium is exactly the same as the surface is turned into a Porous layer of Aluminium Oxide, it's dipped into a coloured Dye solution then dipped in hot water to seal the surface and harden it.

Not to be confused with any process that adds a layer of something different to the surface and makes the part slightly bigger.
Plating, painting etc.

If you electronically strip an Anodised part it will get smaller.