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I spent some time with a headlight restoration kit today...the process for them all is prtty muchthe same:

1 - clean headlights with soapy water, or whatever, and rinse. 2 - remove oxidation and rinse. 3 - wet sand up through a few grits (my kit supplied 1000 and 3000 grit paper) and rinse, and then dry thoroughly. 4 - apply final clear coat.

I have completed steps 1-3, but they (the plastic covers) are just not as clear as I was expecting, i.e. they are still a little cloudy. Is this normal or should they be very clear at this point (which would mean I've somehow done something wrong in this very simple process)?

3 Answers 3

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If they are still a little cloudy, go back and do steps 2 & 3 over again. You haven't gotten through the oxidation layer completely. Once you do them again, I would bet you'll find they are a lot clearer then they were before. Then go on to step 4 and put on the clear coat.

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  • I don't mind doing this, but I did follow the directions, which included using up all of the deoxidation pads/packets that came with it. I don't even mind getting a new kit (although they are stoopid expensive for what you get) but I wanted to make sure I wasn't wasting my time or doing something wrong...it sounds like they should be "clear" before applying final clear coat.
    – AA040371
    Oct 9, 2023 at 22:40
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    If you have sandpaper left, use that ... if all you have is what came in the package, you might get some at 600 grit and use it first, then use the 1000 & 3000 grit again. The sand paper is what does the most when it comes to removing the oxidation. Oct 9, 2023 at 22:47
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Go ahead and do step 4, apply the clear coat.

3000 grit corresponds to stones around 4 microns. In order for something to appear smooth and transparent, it has to be smooth close to the wavelength of light, which is ~ 0.5 microns.

When finishing lenses for things like eyeglasses and cameras, they use a diamond or ceramic polishing paste down to 0.5-0.25 micron (30,000 grit). That's too pricey for some headlight kits, so what they do instead is utilize a clear coat. The clear coat fills in the cracks and coats the surface with a polymer with an optical index close to that of the lens, making it smooth to light.

Often what happens to restored lenses is the polymer wears down and washes out, bringing back a haze. That's why they sell the clear coat alone in auto parts stores, you can clean and reapply it without going through the whole process.

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  • Thanks...you sound like a woodworker...I hear they really have some stones :--) While I may as well go ahead and use some of the leftover sanding stuff to see if I can get a slightly better (clearer) pre-clearcoat result, your explanation accounts for why it probably doesn't make sense to expect a perfectly clear result before apply clear coat.
    – AA040371
    Oct 10, 2023 at 0:04
  • After the clear coat that came with kit is applied, do you think the occasional application of Rain-X (maybe every 6 months) to the headlamps be helpful in forestalling build-up of whatever? It seems like it would, but...?
    – AA040371
    Oct 10, 2023 at 2:41
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    @AA040371 Don't put Rain-X on plastic. The carrier solvent is acetone which is bad for most plastics, including the polycarbonate they use on headlight lenses. Not sure how well the active ingredient, PDMS, bonds to plastic either. Just save the rest of the clear coat, and if that runs out, buy more. I see it being sold as "Headlight Clear Coat" and similar.
    – user71659
    Oct 10, 2023 at 4:00
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You may have made one small mistake; not researching enough as there may be one better solution to polishing and clear coating; acetone vapor deposition.

Here's a clue to final polishing with 3,000 grit; soapy water while polishing. When done, rinse off residue with plain water and look at your results. Water fills in all scratches and makes the lens appear clear. This is the only clue what polishing does as a substitute for and prior to clear coating. After drying off a lens, the haze appears as you're seeing diffraction, scattering light from fine scratches. The clear coat will fill in scratches and allow light thru with very little diffraction - like new. Coating with Rain-x won't help or any other coating. You might have to revisit this again as clear coat wears off since it's plastic paint, not glass.

Search youtube videos on vapor deposition of acetone; a stainless heated cup with a silicone (?) upside down funnel forms a vapor to lightly 'steam' headlight lenses. This is the best way to apply acetone in vapor form (DO NOT SMOKE OR HAVE AN OPEN FLAME!) as it chemically melts plastic lens surfaces to fill in every scratch to like new condition. Acetone is very flammable as a liquid and explosive near an ignition source. I found the video too late as I used a synthetic (Kimi wipes) rag to apply acetone with one wipe to 'melt' headlight lenses into near new condition. The problem is a second wipe melts more and starts streaking that becomes permanent. One swipe over a surface to see the immediate difference. Between wiping acetone and vapor deposition, vapor deposition is superior. No clear coating needed.

Try a small area of your headlight lens with pure acetone from Home Depot, Lowes or local hardware store. Do not use nail polish remover as it contains oil.

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