The dark art of headlight polishing, or why you must seal the surface after polishing

[pinchies]

The dark art of headlight polishing, or why you must seal the surface after polishing

After watching mightycarmods I came away with the impression that headlights can be cleaned easily, using an avocado. Hopefully this post will explain why that is not that simple.

The main issue with cleaning headlights is not getting them shiny - this is readily achievable using a wider variety of methods and tools. The challenge is getting them to stay shiny for longer than a few weeks.

As a soon-to-be chemical engineer, I was a bit interested in the details of what is going on, so I've put some of the more technical stuff in separate sections.
TECHNICAL INFO:
Most headlights are made of polycarbonate, which is a 'soft' plastic - it is impact and shatter resistant, but easily scratched, as your CD collection will testify. To overcome this, OEM headlights come pre-coated with a coating that provides a harder surface (hard as in on the mohr scale), so the headlight can be damaged by fewer materials.

This coating also contains UV absorbers, which prevents damage (photo-oxidation) to the polycarbonate material by solar rays. Polycarbonate, like many polymers, can be degraded by UV light, as the organic polymer bonds absorb UV light. These bonds may then break, but may also produce free radicals, which cause further damage.

Finally, this coating also prevents oxidation occurring on the surface from extended contact with water and air.
END OF TECHICAL INFO

The end result of most abrasive polishing methods is that the OEM protective coating on the headlight is remove, which exposes the headlight to damage at an even faster rate than before - 10 year old headlights might have some damage, but if you just polish them, they will look worse than before you started within weeks, and you will have to keep polishing them.

One product (pittman alr headlight deoxidizer) claims to be able to clean, without the need to remove this coating with abrasives. This claim is partially true, but will not result in perfect results as it does not remove scratches, nor will it replace the UV protective coating. From what I could find, there is a lot of spam/misinformation out there from Jerry Pittman on this product and its miraculous claims, so take a grain of salt with all that you read. From what I have seen, this product is suitable for mild surface oxidation, and in hindsight would probably have been suitable for my car as mine only shows minor surface oxidation.

TECHNICAL INFO:
The pittman alr secret sauce is ... not known, but probably more common than you expect. A variety of materials can be used to remove oxidation, such as some antioxidants. Peroxide (aka bleach) has been shown to work well (see the results of this here, you can login using user topgunner, password topgunner2 to see the pics) but I am confident that the chemicals involved are fairly common - I would bet it would be one of the ones in this list . I guess that the main observation is that this is definitely not a solvent simply melting the surface.
An interesting patent is here, worth reading
END OF TECHNICAL INFO

The question then is: what do I do? The short answer is that replacing your headlights is the only option to get that OEM UV protective coating back... at least that has been the common thought.

From my research (aka extensive googling) the other options available that actually work involve some sort of abrasive/polishing process to resurface the lens, followed by a sealant/protectant. It is the performance of the protectant that is essential for the longevity of the finish.

I have not read of a single one of the common auto 'headlight protectant', 'headlight lens restorer kit', 'plastix', 'Diamondite Clear Plastic Liquid Armor' etc products protecting the finish more than 2-3 months, after reading many forums and amazon reviews. The only options I have found that apparently work for more than a few months (aka, years) are, in no particular order:

1 - clear coat spray, that specifically contains UV absorbers
2 - spar urethane coatings (50/50% volume mixture of helmsman spar urethane clear gloss coating with thinner apparently is highly recommended , but also available in sprays)
3 - UV curing (aka in the sun) headlight spray sealants (here and here both look excellent)
4 - general UV sealants, such as those used on glass (here, used in this kit)
5 - Optimum Opti-Lens Coating
6 - Glassylite Headlight Restoration Kit

Of these options, I eliminated the clear coat spray, as even though it is cheap, I was not confident of achieving the finish quality I wanted. I also didn't want to have to remove the headlights or tape off my whole car.

All of these options appear to produce excellent, long term results.

But... #5 and 6 are a bit special - the others are ok, but these result in HARD coatings that do provide OEM (or higher!) levels of physical protection from scratches, not just the UV protection. The problem then is price... #5 & 6 are both very expensive in Australia!

More info on #5 & 6:
#5: Opti-Lens Coating
#6: GlassyLite â„¢ - Premium Headlight Restoration Treatment

I am now selling a bunch of glassylite kits (includes everything you need!) in the for sale section that I got imported from the US for half the price of retail, if anyone is interested.

I would like anyone's feedback on your experiences if you have tried any headlight restoration method, and the results you got.




Good general references:
Which product to best seal restored headlights? - Auto Geek Online Auto Detailing Forum

Technical references:
UV Inhibitors in Polyester Gelcoats
Why use Light Stabilizers? - UV/Light Stabilizers Center - SpecialChem4Adhesives
https://en.wikipedia.org/wiki/Photo-...on_of_polymers

Really technical references:
Evaluation of UV inhibitors in polyester gelcoats - Capanescu - 2003 - Advances in Polymer Technology - Wiley Online Library
Patent WO2006131469A1 - Tris(hydroxyphenyl) triazines - Google Patents

Lists of UV stabilisers
Light stabilizers / UV absorbers, PC, Polycarbonate, Additive Selector - The Online Experts on Polymer Additives & Colors
Stabilizers - Polymer Additives | Sigma-Aldrich

[Wolfgang]

Polish then apply a coating such as 22PLE, CQuartz, etc.

Simple.

[pinchies]

I havent tried either of those products -- they sound great from a hard-coat perspective, especially for newer cars with protective OEM layer intact -- but neither claims to offer uv protection to the surface underneath. Unless they do, they wont stop the headlight re-yellowing or hazing over permanently, and they are pretty pricey to waste on your headlights if they don't even work! Maybe they do contain uv blockers, but they certainly haven't advertised it. This is compared with other products (e.g. jetseal 109) that do specifically mention UV block - and the proof is in the pudding:





Haven't had a whole lot of interest in the glassylites sadly, so I'll just have to chuck them on ebay once I get the time.

[brad]

Haven't had a whole lot of interest in the glassylites sadly, so I'll just have to chuck them on ebay once I get the time.

Put them in the for sale area

[pinchies]

They're already there Brad! see here

I've sold out of all glassylite.

[brad]

Sorry, realised afterwards that you'd provided a link. Couldn't be shagged editing my post. cheers