As I´m also a fan of OG finishes I gathered some info over the last years sending parts to 2 different companies for anodizing. Happy to be corrected of course, I´m not a chemical engineer.
Silver/clear ano is one and the same, it´s just anodizing without colouring afterwards. It usually goes like this: Surface treatment (polishing- brushing etc), etch bath in NaOH or similar to prep the surface (can also be used beforehand to remove old ano), anodizing to the preferred surface thickness, colouring ("silver" is not a colour).
Aluminium does develop an oxide layer just being exposed to air. Ano is just thicker and a much more robust oxide layer. The etch bath is mandatory before ano not only to remove contaminants but also to get rid of the "natural" oxide which does nearly nothing in terms of resistance to scratches. The longer the part is exposed to the bath, the duller the finish will get. So even a fully polished part will get a bit duller. This can be corrected afterwards to some degree, but you can´t polish too much. That´s why it´s important to have clear communication with the chosen company.
The XT 730 cranks are just anodized from factory, as far as I know the XTR 900 have an additional clear coat (lacquer). I think the latter could also be coloured in a light grey? Not sure as I never compared them. The XTR logos should indeed be lasered. There is no way the cranks came directly from casting (thought they were also forged?) to anodizing without polishing. Every tiny scratch will show up afterwards, even more so as the oxide layer is partly growing on the surface. IIRC 1/3 of the layer grows "outwards", 2/3 into the surface.
The XT cranks I had done came back a bit duller than factory as I thought I had to prep the surface to the desired end finish and cut the polished arms with some fine 3M.
The results after ano can also vary depending on the alloy the part is made of. In my experience the Shimano cranks give no problems here.
De- anodizing at home. Cranks were silver, turn black-ish in NaOH
Surface after etch bath. White residue is grease to protect the threads
Polish&cut back
Slightly brushed finish in the end, but happy nonetheless
Deerhead crank fully polished beforehand, but some small surface defects possibly due to alloy
Sorry for the massive post, but I struggled myself to get some on-hand info before attempting this.
Eager to see how your XTR cranks turn out
@d8mok!
