Pitting & reanodising window frames

Seeking advice from anyone who has bright anodised their aluminium window frames (LWB)

The original frames were scratched so we had them dip-stripped of the old anodising & polished. Some minor pitting (oxidation) revealed itself on the “outside” of the frame (surfaces that were exterior). Looked acceptable.
Had them bright anodised. Now the pitting appears accentuated & more widespread on the exterior surfaces. Not the improvement we were looking for. The interior surfaces look perfect.
Could it be that the polishing left residue in the pits & the anodising didn’t coat those areas? I realise the anodising won’t “fill” the pits. Didn’t expect it to.

What now? Go again? Strip … polish deeper to remove the pitting … and reanodise?

Appreciate any input from those who have been here.

Someone in this vast group must have experience in re-anodising window frames?

shawn at tru6

Thanks! I’ll contact him.

My anodiser said this is a common issue with reanodising. I believe you repeat the process but still not guaranteed to work a second or third time.

I just got off the phone with Ed Mcnamee of Fuchs Restoration (https://www.fuchsrestoration.com/cars-for-sale) he's in the process of offering window frame restoration including bright-dip anodizing. I suggest you give him a call to discuss.

Hi 911GP,
I thought I replied to your comment but it seems to have vanished ….. so to repeat myself :D

Yes, your comments align with others’ observations. I’m learning that the pitting caused by the aluminium oxidising can be like borer - and the depth can be deceptive to gauge.
It’s interesting to note how perfect the inside of the frame is, not having been exposed to the elements, even after all these decades. Also how “concealed” the oxidation/pitting can be - the only defects on the frame prior, appeared to be some medium scratches which were removed by polishing. Once polished, minor pitting was barely evident, but after anodising it was markedly amplified.
I’m going to try sanding one piece of the frame, machine polish and see what result I obtain. If I can remove the pitting without ruining the surface contour, then I’ll try anodising again. Fingers crossed.

Thanks blucille. I’ll give Ed a call - learning never stops.

Thanks for the responses Mepstein, 911GP & blucille.
I ended up stripping & sanding the frames with 240 / 400 / 800 / 1200 grit. 240 on a multi-tool and the others by hand, then finishing off with Meguiars Mag & Alu polish - essentially what the polisher could have done first time around. A satisfying day in the garage.
4-5 tiny pin-hole pits (the pitting ran deep like borer) but you have you have to know when to stop. And they are hard to see unless you know where to look.
Re-anodised. Now as perfect as I could expect them to be! The outsides look like the insides.Attachment 577060
Lesson learnt: polish them yourself next time! I hope there’s not a next time! ;)