Restoration method for blackening plastic material ?

[Greybeard]

Is there a restoration method for blackening plastic (analog to bleaching by H₂0₂)?
The original plastic material has discoloured/greyed by sun light and/or contact with human skin...

[BILLPOD]

I've found any automotive wax works 'to a degree' but I don't believe anything will bring faded black plastic to new condition.   Armorall
does a quick job, but doesn't last as long.   Then there is always the black paint option.

[tszaboo]

I don't know, it seems to happen to multimeters like the 3458A or oscilloscopes like the MSOX 3000G series, and honestly I have no idea how to get back the original nice grey finish instead of the black. I walk myself out.

[HalFoster]

The classic way is to make a mix of hydrogen peroxide and water, put in UV light (sunlight) for a few hours.  This will usually do a very good job of removing the yellowing.  There are several methods that can be found via a web search.

Hal

[audiotubes]

I can't remember the brand and I don't know if it's available in Europe, but there used to be a hammertone office-grey paint used in the po-man's car resto business which might be a good choice for that.

[Greybeard]

The classic way is to make a mix of hydrogen peroxide and water, put in UV light (sunlight) for a few hours.  This will usually do a very good job of removing the yellowing.  There are several methods that can be found via a web search.

I know this method for whitening yellowed plastic that was originally white or grey.
Does it also work on greyed (originally black or dark grey) plastic and does it restore the original colour?

[Jwillis]

Depends on the amount of fading and damage. Very long term UV exposure can cause pitting in the plastic. This is because The UV light breaks down the polymers which then oxidize  which makes the plastic brittle and and changes how the light reflects. Also the oils within the plastic leach away much faster in direct UV exposure and high temperatures.   
Olive oil, mineral oil or linseed oil can restore faded black plastics if the plastic hasn't gone to the point of pitting. A small amount rubbed into the surface often works on sun faded plastics on vehicles. 

[langwadt]

what type of plastic?

[David Hess]

I would try applying methyl salicylate (oil of wintergreen), which works to restore rubber, but I have no idea if it will be helpful for plastic.

[Greybeard]

I'll try to answer your questions:

-what type of plastic?
I don't know what type of hard plastic exactly it is (I can't scrape off some of it to determine it).
It is an eyepiece of a microscope (not the rubber type).

-UV light breaks down the polymers which then oxidize  which makes the plastic brittle
It is not brittle, the surface seems to be as usual but just a bit decolourized.

-oil of wintergreen
Where can I buy it?

[Shock]

Depending on the plastic heating is it one method I've seen. Do and try at your own risk, I suggest testing.

[Greybeard]

OK, the heat gun method. I've seen car parts healed by that.

I'm not quite sure, how much heat ocular lenses can stand...
I'll try to shield the lenses and the rest of the ocular in some way.

[David Hess]

-oil of wintergreen
Where can I buy it?

Amazon has it for not too much.

[jpanhalt]

Methyl salicylate (oil of wintergreen) may cause a burning sensation on skin (think of athletic balm).  While it is not particularly harmful, I would not want to get it on the tender skin around my eyes.  It has no magical properties.  Other oils and plastic restorers will do the same.

It might be good for discouraging mice, though.

[Greybeard]

Thanks for all your answers.

I ended up using Ballistol oil. It spreads easily, is absorbed immediately and works immediately (the plastic is now jet black).
Unfortunately the surface is a bit greasy, which I wiped off as best I could.
It does not smell or irritates skin.

Let's see how long the blackening effect lasts (if necessary the procedure can be repeated).



https://de-m-wikipedia-org.translate.goog/wiki/Ballistol?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp

[HalFoster]

For faded black plastic, the best thing I have found is Mother's Back to Black.  Very good results and actually improves the look of other color plastic as well (just not clear.)