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Old 9th Sep 2020, 6:14 pm   #1
G6Tanuki
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Default Cleaning discoloured coloured/printed plastic.

I've got a Pye AC200PU power-supply here - this was the 1980s-era unit used to convert a M290/MX290-series mobile radio for use as a desktop base-station.

It's clearly had a hard life but has cleaned-up well, except for the plastic strip that runs along the top of one of the extruded-aluminium case parts.

See below - it's gone a nasty yellow. It should be the blue you can see at the edges (which have been covered by the edges of the slot it slides into).

Any suggestions about how best to restore overall blueness without damaging the - presumably moulded-in - text? I've tried washing-up-liquid and bleach so-far without success.

The problem isn't tobacco-staining - this unit came from an environment where smoking on-site would get you fired instantly!
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Old 9th Sep 2020, 7:18 pm   #2
Bazz4CQJ
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Default Re: Cleaning discoloured coloured/printed plastic.

If you're convinced that chemical cleaning won't do it, that leads towards abrasives; people are always polishing up plastic headlights these days.

If the retaining fixture caused the shadowing, maybe it was light (esp sunlight) which has had an ageing effect

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Old 9th Sep 2020, 7:46 pm   #3
G6Tanuki
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Default Re: Cleaning discoloured coloured/printed plastic.

There's no adhesive used - the plastic strip simply slides into the end of a channel in an extruded-aluminium moulding.

It slid out of its channel with only a gentle finger-push, I then tried to clean it with washing-up liquid and then bleach, to no avail.

The channel is sort-of like a laterally-squashed letter C; the 'proper' blue you can see on the edges of the plastic is where it has been under the slightly turned-in retaining edges of the channel in the aluminium, which has protected it from the elements. The rear side of the strip is consistently blue too.

I'm thinking of first giving a go to one of the 'oxygen' stain-removal gels and exposure to the UV of sunlight - a technique I've seen here recommended for dealing with the yellow discolouration of monitor-cases, mice etc.
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Old 10th Sep 2020, 9:08 am   #4
Petedox
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Default Re: Cleaning discoloured coloured/printed plastic.

I would give the gel a go. You can also use hairdressers hydrogen peroxide cream, which is fairly mild, spread evenly and expose to UV light for a few hours.
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Old 10th Sep 2020, 11:17 am   #5
Goldie99
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Default Re: Cleaning discoloured coloured/printed plastic.

The original plastic will have been formulated with either a blue pigment, or a blue dye, and quite possibly UV stabilisers (esp. if it was intended for exterior use). What I suspect has happened is UV degradation - the stabilisers get depleted over the years, with UV exposure, and eventually can no longer protect the plastic, or the pigment / dye. If so, it's irrevsersible.

Unfortunately, I think your best option for a good result is to scan the text, and make a replacement. Either way, if you scan it first, you then have little to lose in trying any cleaning techniques.

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