Trying to spruce up some raw aluminium forks, and all over them it has these dark blemishes, that neither IPA or warm water with a bit of white vinegar in will shift. Any particular polishes I should be looking into?

I’m no metallurgist but I reckon that’s likely to be aluminium oxide. Once that’s present even when you scrape it off the raw aluminium underneath just reacts with oxygen in the air and it comes straight back. It’s not particularly agressive in the same way that rust is so not necessarily a worry, but I guess it’s unlikely you’d be able to treat it successfully without some kind of galvanisation.

galvanisation

I think that is specific to iron and steel, aluminium is more often anodised. I think it’s going to need a proper polish first though

@tomhoward why don’t you splash a little of your immense wealth on having them cerakoted? I’d love to know how durable that stuff is

I’ve always had a tube of Halfords /autosol metal polish in my tool box for about 25yrs that does a great job of polishing up bear metals.

https://singletrackworld.com/forum/topic/raw-aluminium-frame-options-for-protecting-it-clearcoat-anodising-or/

You need some Scotch Brite pads and elbow grease. I own two raw aluminium frames and keep on top of them with light polishing using fairly mild Scotch Brite pads. You’ll end up with a lightly brushed finish. If you want highly polished then continue the process using fine steel wool with Autosol polish or Peek metal polish. Final step for me – and I’ve only done one frame so far – was acid etching it using phosphoric acid, to prevent further oxidising.

Scotch Brite pads I use:

‘Red’ pad, #64659, very fine – this is apparently the pad supplied with new Geometron/Nicolai frames for refinishing.

‘Grey’ pad, #64660, ultra fine – slightly finer than the red pad, I used this to finish my Geometron ahead of acid etching it.

End result from red pad, grey pad then acid etching:

Edit: next on my list is to polish the remaining black finish off my crank arms (half-removed with the usual heel rub) and acid etch them too.

Nah, you need a new bike mate.

Nice job Ally – one point though, Geometron frames are 7020 aluminium, which is different to the 6-series alloys most other frames use, so they oxidise less/differently. Fork lowers are most likely different again, with lots of magnesium, so again will behave differently

Re the acid etching – how did you do that? Assume you don’t have a massive tank of acid to dip the frame in?

I’d be surprised if forks were raw aluminium, they would get corroded very rapidly. They might be anodised with no dye. If corrosion has broken through the surface I don’t think there’s much you can do except smooth it off to minimise wear on the seals.

Nice job Ally – one point though, Geometron frames are 7020 aluminium, which is different to the 6-series alloys most other frames use, so they oxidise less/differently. Fork lowers are mst liekly different again, with lots of magnesiu, so gaint will behave differently

Thanks, I’m happy how it turned out and it seems to be holding up very well. Despite the 7020-T6 my Geometron was staining badly beforehand mainly with me being a sweaty bstard. Perhaps not oxidising – I’m no metallurgist – but it was frustrating after initially going for a much shinier finish when I first bought the frame. The previous owner preferred to ride it as intended (and produce a DH podcast) than polish it, but I must be more of a tart than George 😃

Re the acid etching – how did you do that? Assume you don’t have a massive tank of acid to dip the frame in?

No tank – can you imagine the size of tank needed for an extra-longest Geometron 😃. Big sheet of polythene underneath, frame clamped in old workstand. Used a heat gun to warm the frame as I was doing it outdoors, in Scotland, in January, but not sure if strictly necessary. Using a 500ml bottle of phosphoric acid bought online, wiped it on with a microfibre, left it a couple of minutes, then carefully washed off with soapy water. A mate successfully did a couple of his frames previously using this method and turned out OK.

Cool, that’s interesting – and it has held up well?

Might be wasted on me, mine lives under a layer of dirt, I mainly wash chains and cassettes, and just brush off the worst elsewhere

Cool, that’s interesting – and it has held up well?

Early days. Mostly rode my other bike through the winter so it’s only done maybe a dozen rides since, but they’ve been filthy, hard rides. Picking up the usual scuffs from use but no staining/permanent marking, the real test will be in warmer conditions when I’m dripping sweat all over it.

Hope it’s been worth it. TBH wasn’t that time-consuming but it’s still extra work I’d not have to do on a painted frame (as it’s been pointed out repeatedly by some mates).

I’d be surprised if forks were raw aluminium, they would get corroded very rapidly.

Correct-ish – raw aluminium is very reactive so pretty much everything we think of as aluminium is not; it has a self protecting thin layer of oxide over the top.

So if your forks were raw aluminium, very quickly thereafter they’d be passivated aluminium and therefore won’t corrode – they don’t need to be anodised or coated to protect them.

I’d try a fine grinding paste on those blemishes, or a fine wire wool or scotchbrite, to remove whatever is on the surface that is causing the discolouration, then the dull grey aluminium oxide will come back.

For speed, you could also use oven cleaner plus a scotchbrite, but wash off well after.

First suggestion is try an abrasive block – we use garyflex 240 fine on our aluminium profiles.
That or cream cleaner and a cloth.

Bear in mind that the raw finish you have there doesn’t look raw at all but quite heavily polished so you’ll need to buff it once you’ve got rid of the mark.

Are you still in/round Harrogate? I’ll see if I can find any offcuts of raw (which is it say mill polish, ready for treatment) for you to attack with various things, and see how quickly your finger prints etc mark the damn stuff.

Soda blasting works well. It is as described. Blasting with bicarbonate of soda. Will polish up after that .

Brasso.

Thanks all,

After further enquires, I think they’re clear anodised, so not a lot can be done, luckily it’s not on the stanchions, so functionally they’ll be fine, and the blemishes are only noticeable up close.

Not sure how well cerakote etc would work @rubber_buccaneer, as there’s millions of ridges, so the finish would likely be a bit meh.

Have they been like that since day 1 or is the blemish “developed”?

Developed I think. Though I haven’t had them from new. I can’t imagine Intend would let them go out like that, and they have changed the manufacture since.

Hmmmm

Looking at the mark, I’m guessing it’s a cable tie – looks like two parallel lines with a square bump part way? Probably holding one of those silly Enduro mudguards things that make a mess of (edit) fork lowers.

I’d be tempted to give them a go with an abrasive to be honest, then lacquer over (assuming you’re not wanting to get them stripped back and re-anodised). Try it somewhere out of sight first!

(edit: yeah that auto correct needed putting right!)

or is the blemish “developed”?

I’d call it the patina of their rich history

It’s not just that blemish, there’s a few all over, will get more pics later.

I’d call it the patina of their rich history

I’ve got a few of those

It’s not just that blemish, there’s a few all over, will get more pics later.

If you are still here abouts I’ve plenty of bits of satin anno silver, raw, and possibly even a bit of clear anno if I can manage to get the box down so you can have a bash at some without running the fork.