Polishing perspex - cleaner?

[Another John]

We've just reassmebled a very large (6'h, 4'w, 1'd) perspex cabinet for the historical collection for which I work. The material itself is solid perspex sheets (about 8mm thick), bolted together: it's a wonder of smalscale precision engineering.

The sheets had all been wrapped in cling film for storage - to keep them dust- and scratch-free. We didn't know at the time that they would be stored for FIVE years!

The patterns of the cling film (clinging to the sheets, and to each other) have "etched" the patterns on to the shiny surface of the perspex.

The plastics experts on the internet (so far) say "never use anything but soap and water", and microfibre cloths to polish perspex. Well, soap and water's no good for this job (I found, after half an hour on one square foot), so I bought some spray-on window spray: also no good. My elbows have been thoroughly de-greased this afternoon.

Is there anything that has a teensy bit more bite (preferably something for the job) that I might try? My plan for the window cleaner was to use it, then (having succeeded) wash that off.

The display case is useless if it is not crystal clear, so these beautiful big sheets of perspex may be heading for the tip :-(

Cheers John

[Colin Bignell]

I would try polishing it with whiting powder.

[Theo]

Are you sure it's an etch into the surface, rather than something sticking to the surface? For the former there's nothing for it but to remove further material to get a flat surface, for the latter a solvent might dissolve the gunk without damaging the surface.

As to what solvent, depends what the residue is. For sticky labels and such I've had good results with cooking oil as an oil not water based solvent (scrub with a brush, wash off with washing up liquid), and doubt it would attack the perspex. IPA is stronger but I think it wouldn't damage it.

Do you have a piece you can try things on without it mattering?

If it is actually etched, I've used toothpaste to polish out scratchea, but there are better products. See guides for how to de-fog car headlights, which are the same material.

Theo

[Animal]

You can always use the same methods used with fogged car headlights. (There is also flame polishing, but I would definitely not recommend it here.)

[Cursitor Doom]

T-Cut or something similar. It's a cutting polish intended for this kind of thing. Whilst normally used to re-vitalise car paintwork that's dulled, it can be used on perspex as well. It will involve quite a bit of elbow grease if you're doing large areas, but I personally would use a rotary polishing mop to speed things up.

[Spike]

In order to defog my car’s headlamps, I use a microfibre cloth dampened in warm washing-up water, applying some toothpaste, and using some elbow grease rub into the plastic. Every now and then rinse off with said washing-up water, turn the cloth, and start again. Finally, rinse with clean washing-up water, dry, and rub with a cloth well dampened with IPA. After three years of MOT advisories, the last one didn’t mention the headlights at all.

[Jim the Geordie]

My garage uses T-cut and water

[alan_m]

T cut would probably be too aggressive and leave too many fine scratches. there are other polishing compounds for car paintwork finishes that are a lot finer.

[The Natural Philosopher]

Again there are kits for polishing headlights that will work fine.

You need a fine abrasive - a scouring powder like ajax and a buffing wheel might work

[HVS]

On 03 Feb 2024, alan_m wrote

What about jeweller's rouge?

[Animal]

You really don't need a wheel/machine, perspex/acrylic cuts very quickly.

[Another John]

As so often Theo I think you may be bang-on: this may be gunk, not etching.

I have had suggestions from other friends: WD40, Contact cleaner, and a "Magic Sponge" -- a weird thing I'd never heard of before, available under various names, but I've just bought two packs of 4 from Yorkshire Trading Company: a quid each pack.

I can't get at the panels/cabinets today to experiment, but I have an old perspex picture frame here at home, which is very crusted with dust of decades and which I scribbled on with a "permanent" black felt pen, and also with a permanent Sharpie:

WD40 - removed everything, with a little persistent rubbing. A faint shadow of the pens remained which would have come off if I'd continued rubbing I guess.

Contact cleaner: removed everything, _instantly_.

"Magic sponge": removed the dust gunge, but didn't do much on the pens, so I used the contact cleaner, and again: it went _instantly_.

I washed the perspex with washing up liquid immediately, then rinsed. I'm now waiting to see if there's any further reaction.

Those magic sponges seem like they'll have a use in the future! What the hell are they?? It's a pretty insubtantial sort of sponge material, and you use it like a normal sponge: dunk it in plain water.

Of course: my frame may not be the same sort of perspex as the cabinets, but tomorrow I'll test the three solutions.

(Apologies for wittering on!)

Thanks SO much everybody! There's nothing like Usenet for _useful_ discussion!

John

[jkn]

"Magic Sponges" are a melamine foam. The material itself is extremely hard, but in sponge form microscopic parts break away in use. I presume the reason they are so effective for some things is that the new surface exposed continues to be very hard and sharp.

They are pretty handy things; as long as you remember they are an abrasive, albeit a very fine one. I try to keep a few around, they certainly have their uses.

[Dave W]

The trouble with polishes is that although the result is shiny, it's also 'wiggly', i.e. acts like a concave lens, which would not be acceptable in your application where the subject matter is a long way behind the perspex.

[Sn!pe]

Brasso works for me.

[Sn!pe]

Oops, apologies for posting to stale thread.

[nick]

If you have any actual scratches then the suggested very fine abrasive should deal with them. As for getting an overall smooth sheen on the Perspex surface, we used to use a lambswool polishing bonnet applied very lightly so as not to burn in any new marks. Mind you, our Perspex sheets were much smaller than yours so you've got a bit of a job on there!

[Another John]

OP here - replying to my own post:

I finally cleaned the cabinet last week (or so -- time flies so quickly ... and yet I never do anything [exciting]!)

I decided _not_ to risk the magic sponges: they are mysteriously magical, but it would have been a disaster to have got even one smear of micro-abrasive damage on the cabinet.

(By the way the cabinet was in its component pieces, which made cleaning it infinitely easier than the other one I'd done a few weeks ago, which had already been re-assembled).

I decided to take the slightly smaller risk of using the electrical contact cleaner, applied with a new microfibre cloth. This removed the 'gunk', sometimes with a bit of persistence, but usually: like magic.. I then immediately cleaned the surface again with mildly soapy warm water (different cloth of course). Then I cleaned it again with clean warm water (different cloth again). Then I dried it and polished it with another cloth.

To tick the last box here I hope: to clean it, I laid each sheet (some measuring 6' by 2') on a table, on which I had laid a thick towel. I also had to prop them up against the window, at the last stage, in order to see any remaining small patches of gunk, some of which had to be given the contact cleaner again before disappearing.

Cheers and thanks for all the proffered advice! John