ddieringer

This procedure works on heavily pitted lenses (like one of mine), but not for cracks or deep rock chips.

Before and After


Most of the pictures below show my DIY LED Daytime Running Lamp installed in the fog light housing.
See my DIY LED DRL Tutorial Here.

You'll need a few common tools and supplies and one specialty product.

The specialty product you need is Cerium Oxide powder - it is available on the Interwebs for pretty cheap. I bought four ounces for $10, including shipping.
Just add some water to a small amount of powder until you have a runny paste. Apply it with a heavy cotton/felt buffing wheel or dense foam wheel (probably a better choice since it won't soak into the foam as much).
Four ounces is enough to do literally dozens of lenses and seems to work just fine and incredibly fast on plastic/acrylic lenses too.
It is used commercially in auto detailing and glass jewelry making. Your local glass shop or specialty "rock shop" jewelry store may be willing to sell/give some to you. You won't need much.

Regular polishing compound will not work on glass lenses- order some Cerium Oxide.

Buy decent-quality sandpaper. I started out with some cheap stuff I had laying around. Go get the good stuff right away.
I also started with 180 grit, and it took a long time to get all the pitting removed.
I eventually switched from using the battery powered drill to an AC-powered Makita - I could use more pressure and still keep relatively low RPMS (lower RPMS = less heat).


WARNING:

• Make sure you wear PPE (personal protection equipment) appropriate for polishing glass
• Cerium Oxide may contain trace amounts of radioactive material at concentrations slightly higher than background levels - do your homework
• A proper respirator is a good idea - the glass will come off as a powder, though wet sanding keeps it (mostly) from being airborne
• Ear protection is wise - the drill motor is high pitched and will be running for hours
• Eye protection, goggles, or a face shield might make you more comfortable. The water and polishing compound get everywhere
• I also used an old bathroom towel on the floor under my work bench and covered nearby items with towels and plastic.

MORE WARNINGS AND NOTES:

• Heat is bad and builds up from friction - don't work the same place for too long or at a high speed
• Always wet sand - keep the lens and the sandpaper wet
• If your water evaporates immediately, use a slower speed
• A few drops of dish washing detergent in your spray bottle seems to help enormously
• Glass is hard and durable - you'll need to use a decent amount of pressure, especially with high grit (low number) sandpaper. Be certain your work is properly clamped
• It may not be possible to properly polish the entire contour of the lens with the fog light assembly still installed in the car, never mind the actual risk of slipping and damaging the finish on the car. Just take it out
• You will not be able to hold the lens in one hand and the drill in the other while applying any useful pressure. Just clamp it
• In order to clamp it securely you'll need to remove the entire housing from the car - clamping just the lens is inviting costly damage

I used this time as an opportunity to also repair damage to the fog light housings - I will post a separate write-up.



Before
I started with one nearly perfect lens, and one pretty terrible one.






Tools
I eventually switched to using an AC-powered Makita that could still spin at relatively low speeds even when using heavy pressure.






Sanding
I started with 180 grit and spent a long time - about 90 minutes - removing the severe and dense pitting. In hindsight, I might have wanted to start with a coarser grit. Regardless, take your time and get it as close to flawless as possible.

I spent ~20-30 minutes with each of the subsequent grits - 220, 320, 400, 600, 1000. In hindsight, I should have spent a little more time using 220 grit. The few remaining correctable imperfections amount to "swirling" likely introduced when using 180 grit. I attempted to photograph these imperfections in the finished result, but the photos did not clearly show what was there. I opted to describe it instead.

It's difficult to see much difference in results after using each grit, but you can feel the smoothness improve with your fingertips.








Finished
The lens looks pretty good, especially considering the condition when I started. I am convinced that spending more time during initial preparation (ie, with 220 grit) and even more time with the Cerium Oxide would result in an essentially flawless result.
This got to be "good enough" for me after about four hours. Besides, my arms were tired from using the drill and pressing for so long. Splitting the work over several days would be a great idea.





Plastic Side Pieces
Of course, now that the lens looks good, the side pieces look absolutely terrible in comparison. It takes almost no work or time to get these looking good. I attached them to the fog light housing so I could more easily polish them in one step using only Cerium Oxide.

In order to fully remove the cleaning compound, though - which has a tendency to go everywhere - you'll need to carefully disassemble each of the side pieces after you polish them. There is a clear plastic backing system on each one that can be removed by carefully prying with a tiny flat screwdriver.






Totally Finished


It is labor intensive and a little messy, but the results are pretty wonderful.

To see them installed on the car, see my DIY LED DRL Tutorial Here.

fejjj

Thank you for sharing this!����

Arominus

Ive got one bad and one great lens, looks like i'm ordering some Cerium.