Safe treatment of oxidized die-cast aluminum?
February 19, 2019 11:32 AM Subscribe
My SO has a turntable platter that’s made of die-cast aluminum. It has a greyish film in spots that I gather is oxidization (?). What are the best products (or ingredients) to treat it (clean it without damaging the finish, prevent further oxidization, make it look good)? What should be avoided?
Apparently some people use Brasso, some never do and only use aluminum-specific stuff (what would that be?), some use lemon juice or vinegar, some say to never do that, something something alkaline (have seen both yes and no to that), sandpaper (same), cream of tatar, Arm & Hammer (same and same). No consensus online IOW.
We’re in Canada. Looking for products or ingredients you could easily get at Home Depot, Canadian Tire, Amazon.ca, etc. We don’t have access to any kind of blaster or other machine. Wouldn’t like to spend too much.
Apparently some people use Brasso, some never do and only use aluminum-specific stuff (what would that be?), some use lemon juice or vinegar, some say to never do that, something something alkaline (have seen both yes and no to that), sandpaper (same), cream of tatar, Arm & Hammer (same and same). No consensus online IOW.
We’re in Canada. Looking for products or ingredients you could easily get at Home Depot, Canadian Tire, Amazon.ca, etc. We don’t have access to any kind of blaster or other machine. Wouldn’t like to spend too much.
Aluminum naturally forms an oxide layer, which unlike steel is protective and in a non-marine environment won’t consume the material. Unless it’s really pitted and uneven, you can leave it alone. If it’s too serious, gentle wet sanding to smooth out the finish and then polish with Noxon.
posted by a halcyon day at 12:11 PM on February 19, 2019 [2 favorites]
posted by a halcyon day at 12:11 PM on February 19, 2019 [2 favorites]
A long time ago I used to use a product called Simichrome on aluminum parts of my motorcycle engine.
posted by under_petticoat_rule at 12:35 PM on February 19, 2019 [2 favorites]
posted by under_petticoat_rule at 12:35 PM on February 19, 2019 [2 favorites]
Best answer: Most turntable platters like this have a thin layer of laquer to protect the finish. While you can clean these with Brasso it will take quite a while (like an hour of scrubbing by hand) to get through the laquer to the alloy metal below.
With or without laquer it is strongly recomended that you avoid touching the platter with fingers as any sweaty fingerprints can become permanent.
Once polished a platter will look good for about 6 months - but without laquer it will tarnish again and probably far worse than before. So you have 2 choices, either keep polishing it twice a year or polish it once and try to replace the laquer. Adding laquer is where this gets tricky as it is very easy to add just enough weight in laquer to throw the turntable out of balance.
Manufacturers generally recommend you don't attempt this, they will instead recommend you either live with it (embrace the patina) or just buy a replacement platter.
I think there is a reason that none of the major manufacturers sell platters that are polished/shiny when new and that is that the duller finish degrades more gracefully over time.
posted by Lanark at 2:24 PM on February 19, 2019 [5 favorites]
With or without laquer it is strongly recomended that you avoid touching the platter with fingers as any sweaty fingerprints can become permanent.
Once polished a platter will look good for about 6 months - but without laquer it will tarnish again and probably far worse than before. So you have 2 choices, either keep polishing it twice a year or polish it once and try to replace the laquer. Adding laquer is where this gets tricky as it is very easy to add just enough weight in laquer to throw the turntable out of balance.
Manufacturers generally recommend you don't attempt this, they will instead recommend you either live with it (embrace the patina) or just buy a replacement platter.
I think there is a reason that none of the major manufacturers sell platters that are polished/shiny when new and that is that the duller finish degrades more gracefully over time.
posted by Lanark at 2:24 PM on February 19, 2019 [5 favorites]
Best answer: As a halcyon day said, aluminium naturally (and almost instantly) forms a protective hard oxide coating that's usually best left alone.
It is however slightly porous on the surface, and will tend to absorb contaminents like salts & oils from handling which, over time, can add up & dull/change its appearance in spots. That goes double for die-cast aluminium, which has a rougher surface than machined/polished aluminium & therefore somewhat more surface area to absorb/hold crud.
I don't know of a guaranteed foolproof way of cleaning such handling/contamination spots off die-cast aluminium. The problem with using things like polishes or sanding is that they change the surface texture, smoothing out the naturally rough surface & creating shiny(er) spots that stand out like dog's proverbials against instead of the natural grey die-cast surface.
Without polishing the whole damn thing (which will totally change the surface finish & look, but at least it can be made even), you want to clean the salts/oils/whatever from the porous oxide surface. And doing that as gently as possible is dependant on knowing what the contaminant is…
(On preview: Lanark also makes a good point, but it depends on the manufacturer & age - at various times the fashion has been for polished, unpolished, or die-cast finish; sealed, anodised, or natural, etc. Determine exactly what the finish is before attempting to fix it.)
As a first guess, if it's unfinished die-cast aluminium then marks on a turntable platter are probably mostly from skin oils or salts. I'd start with plain water, and work my way up through mild detergent, methylated spirits, naptha / white spirit, then actone or toluene. If none of those worked, I'd be tempted to sit and think about whether what I wanted to achieve was worth the chance of a worst-case outcome (i.e. the whole thing looking unevenly dull and splotchy) - and if so, bring out the caustic cleaners. They'll break down most organic contaminants, but at the risk of affecting the existing protective oxide coating.
posted by Pinback at 2:45 PM on February 19, 2019 [2 favorites]
It is however slightly porous on the surface, and will tend to absorb contaminents like salts & oils from handling which, over time, can add up & dull/change its appearance in spots. That goes double for die-cast aluminium, which has a rougher surface than machined/polished aluminium & therefore somewhat more surface area to absorb/hold crud.
I don't know of a guaranteed foolproof way of cleaning such handling/contamination spots off die-cast aluminium. The problem with using things like polishes or sanding is that they change the surface texture, smoothing out the naturally rough surface & creating shiny(er) spots that stand out like dog's proverbials against instead of the natural grey die-cast surface.
Without polishing the whole damn thing (which will totally change the surface finish & look, but at least it can be made even), you want to clean the salts/oils/whatever from the porous oxide surface. And doing that as gently as possible is dependant on knowing what the contaminant is…
(On preview: Lanark also makes a good point, but it depends on the manufacturer & age - at various times the fashion has been for polished, unpolished, or die-cast finish; sealed, anodised, or natural, etc. Determine exactly what the finish is before attempting to fix it.)
As a first guess, if it's unfinished die-cast aluminium then marks on a turntable platter are probably mostly from skin oils or salts. I'd start with plain water, and work my way up through mild detergent, methylated spirits, naptha / white spirit, then actone or toluene. If none of those worked, I'd be tempted to sit and think about whether what I wanted to achieve was worth the chance of a worst-case outcome (i.e. the whole thing looking unevenly dull and splotchy) - and if so, bring out the caustic cleaners. They'll break down most organic contaminants, but at the risk of affecting the existing protective oxide coating.
posted by Pinback at 2:45 PM on February 19, 2019 [2 favorites]
Response by poster: Once again, I feel fortunate to be a part of such a knowledgeable community! Thanks, all, for your answers.
The turntable was purchased second-hand, so, I don’t know what materials it’s been exposed to. It’s a Technics SL1100, for reference. The specs refer to do-cast aluminum, I’m not sure about finish apart from that.
Here are pics of the platter we have, and here’s what a clean one should look like.
Thanks again!
posted by cotton dress sock at 4:40 PM on February 19, 2019
The turntable was purchased second-hand, so, I don’t know what materials it’s been exposed to. It’s a Technics SL1100, for reference. The specs refer to do-cast aluminum, I’m not sure about finish apart from that.
Here are pics of the platter we have, and here’s what a clean one should look like.
Thanks again!
posted by cotton dress sock at 4:40 PM on February 19, 2019
Response by poster: Argh, *die-cast, not do-cast, sorry! Autocorrect.
posted by cotton dress sock at 4:58 PM on February 19, 2019
posted by cotton dress sock at 4:58 PM on February 19, 2019
Best answer: Good pics 🙂. Looks like it's die-cast and machined - the top surface (where the turntable mat sits) looks machined & uncoated, the sides are finely machined or brushed/polished & look coated with lacquer or something, and the rim (where the strobe dots are) is infilled with paint and probably coated with lacquer too.
Most of the marks look like random crud; dirt and sticky oily gunk just caked on. In fact, I wonder if the turntable mat didn't "go off" and turn all crumbly &/or gooey at some stage - it kinda looks like the gunk from start of that process. It'd probably respond well to very gentle cleaning as I described.
A few tips:
posted by Pinback at 5:47 PM on February 19, 2019 [3 favorites]
Most of the marks look like random crud; dirt and sticky oily gunk just caked on. In fact, I wonder if the turntable mat didn't "go off" and turn all crumbly &/or gooey at some stage - it kinda looks like the gunk from start of that process. It'd probably respond well to very gentle cleaning as I described.
A few tips:
- Examine it carefully for signs of flaked/lifted/lifting lacquer. If it's lifted in spots, it's likely to come off during cleaning & in the future. Consider if you're OK with that possibility, and maybe jumping straight to my last tip…
- The top surface at least should clean up with a gentle touch - cotton makeup pads, wet with the cleaning solution, are good for that - though as I worked my way through I'd probably stop at the metho step & re-assess. It'll be under the mat anyway, so I'd treat it as an 'exploratory cleaning' step to test various cleaners & methods.
- If that works, I'd gently try a few as inconspicuous as possible bits on the sides - e.g. the very edge below the strobe rim - and see how they clean up. Chances are, if the lacquer isn't lifting it'll come up quite well.
- Easier alternate way, if the lacquer & paint all appears intact: soak it in a tub of gently-warm water with just a *touch* of wool wash or fabric softener - literally just enough to get the water ever-so-slightly frothing when you agitate it. Leave it there for a few hours and see if the gunk wipes off easily.
- That said, if I was doing a full restoration I'd consider stripping all the lacquer off, very very gently polishing it, infilling the paint on the strobe rim if necessary, and either (a) leaving it to age gracefully (preferred), or (b) giving it a couple of very light coats of lacquer.
posted by Pinback at 5:47 PM on February 19, 2019 [3 favorites]
(Oh, and I'm assuming in all that that you've got the platter out & free - it looks like you have, but I realised I'd assumed that! Work on the platter alone & separate from the rest, and definitely don't go soaking the whole thing!
And I'm not a turntable expert; I've done a few, but my evaluation & tips are based on general experience with restoring old[er] electronics. If a turntable restoration expert turns up & disagrees with me, I'd recommend listening to them 🙂.)
posted by Pinback at 6:02 PM on February 19, 2019 [1 favorite]
And I'm not a turntable expert; I've done a few, but my evaluation & tips are based on general experience with restoring old[er] electronics. If a turntable restoration expert turns up & disagrees with me, I'd recommend listening to them 🙂.)
posted by Pinback at 6:02 PM on February 19, 2019 [1 favorite]
What’s your goal with the turntable? Just playing records, or cosmetically restoring it?
If the former, the strobe ring should work just fine with a light cleaning, and a new mat will cover the platter surface. It’s more important to replace the belts and stylus, and adjust the tonearm.
posted by a halcyon day at 7:28 PM on February 19, 2019
If the former, the strobe ring should work just fine with a light cleaning, and a new mat will cover the platter surface. It’s more important to replace the belts and stylus, and adjust the tonearm.
posted by a halcyon day at 7:28 PM on February 19, 2019
Your platter looks to have spots with significant pitting on both the side and top. Does a finger nail catch on the discoloration if you scrape over it? If yes I really doubt you'll be able to wash it away with any product.
posted by Mitheral at 11:19 PM on February 19, 2019
posted by Mitheral at 11:19 PM on February 19, 2019
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posted by cotton dress sock at 11:47 AM on February 19, 2019