Polishing old cloudy transparent plastics

[MrBungle]

I have a couple of heathkit items (VTVM + AC Voltmeter) here from the late 1960s where the meter face on them has gone slightly cloudy. Can anyone recommend a way of cleaning these up?

Automotive headlight polish?

[paulsherwin]

Any cutting compound will work, but the cloudiness is often below the surface so difficult to polish out.

[MrBungle]

Thanks both for suggestions. I'm going past halfords later so will have a look for something suitable.

If it's below the surface I'll have to live with it

[paulsherwin]

T-Cut will be as good as anything. I think Halfords do their own version of it, as do Poundland (called 'scratch remover' or something similar).

[Dickie]

The bees knees is Greygate plastic polish, from the people who make "paste polishing no5" for bakelite. Works a treat on removing scratches from perspex turntable covers.
http://www.greygate.com/product/plastic-polish/

The headlight polish has a weeny bit of solvent in it makes for a shinier result, harder work, a bit like french polishing.

[Uncle Bulgaria]

A word of warning - if it's acrylic then a solvent-based polish will likely cause it to craze either immediately or in the near future. There's something in the reaction of the stressed material and the solvent in polishes like Brasso/Silvo etc. that causes this reaction.

I'm wondering the same thing as I need to polish a newly-cut cover. I think a dedicated plastic polish is the way to go, or perhaps a DIY compound involving bicarb or toothpaste.

[MrBungle]

Thanks all. I have a sacrificial very duff cracked one I will try a few things out on I think and see which one works out the best. I will report back as soon as I have an answer!

[David G4EBT]

Nothing ventured, nothing gained, but I think this is the same issue as with Bush TR82s, where the large transparent knob, (sometimes incorrectly described as the 'dial') goes milky right through and no amount of polishing makes an iota of difference. Maybe it's due to damage caused by exposure the sun's rays. Luckily, almost all of the Heathkit meters I've had - AV3-U, MM1-U, V7A-U etc - haven't suffered from this problem.

Good luck with it MrB.

[G6Tanuki]

The problem with the likes of car-headlight plastics is that the plastic progressively degrades/discolours throughout its full depth - so 'polishing' the outer surface doesn't give a lasting cure, it only takes-away the first millimetre of the worst-discolored surface.

Keeping the plastic away from sources of ultraviolet light slows the inevitable transition-to-discoloration, but you can't beat it forever: the tendency-to-discolor is built-in to the plastic at the time of manufacture.

[Karen O]

this is the same issue as with Bush TR82s, where the large transparent knob, (sometimes incorrectly described as the 'dial') goes milky right through and no amount of polishing makes an iota of difference

I wish I'd known that seven years ago! I spent a whole weekend polishing away at my TR82C knob with nothing to show

[Bazz4CQJ]

T-cut is a fairly abrasive material, so if you use it and you're getting a result then changing to something finer may work well. In Halfords, I think that most of the car polishes made by Meguiars show a scale indicating how aggressive they are.

I polished the face of a meter on an old Farnell psu recently and got a good result, the only surprise being that a for some hours afterwards, the pointer on the meter was incredibly sensitive to static charge, but the effect soon faded away.


B

[Argus25]

Most vintage clear plastics go cloudy and yellow on the surface, but as noted, some it is all the way through they yellow or crazed. But, mostly, the degradation is due to the surface layer becoming crazed and scratched.

Therefore, most of these cases, including acrylic, benefit significantly from polishing. I struggled for years with this problem, trying all sorts of automotive cutting and polishing compounds. Some are disasterous as they react with various plastics. After all that I found the 3 step specialist plastic polish made by Novus and available from Antique Electronics USA. After using this, there is no going back. It comes in 3 grades and you need to buy three bottles but they are not that big or expensive. A lot of the time you just need the fine and or medium grade.

With the fine version I managed to restore an oscilloscope acrylic filter and it looks so good, almost new, these show the smallest fine marks and abrasions from people touching them over the years or wiping them with a dry cloth when there is fine grit and dust on the surface, thinking they are cleaning them, but really applying multiple fine surface scratches (don't get me started on this topic).

If the plastic surface is damaged badly, it needs to pass through the three stages or grades of polish. If the surface is very very bad then 2000 grade paper prior to the coarse polish works if the next two grades of the Novus polish are also used. The chemical base in this product, unlike many others not specifically intended for the application, does not react with the plastic.

So my advice after many decades or wrestling with this problem is save yourself a whole lot of headache and go for the correct product designed for the job, rather than an alternative that might or might not work out and even if you think you have succeeded, this polish would have given you a better result.

[Tractionist]

My attitude is 'in for a penny - in for a pound' i.e. if a lens is unusable, then you haven't got much to lose!

I've cut loads of plastic lens's [dials/IR transmitters/headlights etc.] always with great success - except of course TR 82 tuning knobs!

My technique varies dependent upon the extent of damage [pitting/scratches] etc. Worst cases get treated to varying grades of wet and dry paper - but I nearly always finish-off with Solvol Autosol metal polish [which is essentially Jewellers Rouge in a gel carrier]. However - in order to preserve the result, it is essential to finish off with a decent plastic polish.

The only items that I have ever had to do again are car headlight lens's [every three years or so] - these haven't yellowed or gone cloudy ..... it's essentially because they are permanently exposed to the elements [rain, snow, sun ....... and road abrasion]. Headlight lenses therefore sustain much 'micro-pitting' - which makes them look slightly opaque [rather than translucent], and ergo this 'stars out' [refracts] the beam.

[ronbryan]

I have polished out fairly deep scratches on a Heathkit meter just using Brasso applied with folded up kitchen roll. I think it took about an hour. It has to be done carefully because excessive pressure could cause the plastic to crack, as can picking the meter up by the handle with your wrist laying across the meter face!

Ron

[MrBungle]

Excellent info from all. Much appreciated.

[yesnaby]

Edd from Wheeler Dealers did this successfully to car headlights, though the process started by sanding them to become very rough and matt, then several stages with finer and finer sanding/polishing. Seemed to work well.

[Terry_VK5TM]

Many years ago, we used to use toothpaste on Arcade machine perspex.

May not work now with the change in toothpaste formulations

[FIXITNOW]

QUIXX make scratch / polishing kits for Perspex might do the job