Polishing Plastic Headlight LensesPlastic headlamp covers can be saved with a little polish
One of the casualties of the 1970's safety blitzkrieg forced upon American-sold cars was glass headlamp covers. Used to be that durable, sleek glass could mirror the hood profile and streamline the front end (think early Jaguar XK-E). Seems that the glass was a bit of a hazard to pedestrians and in frontal collisions. Apparently one or two Nader ideas made sense, even if the Corvair never recovered. That aside, though, we're now stuck with durable, cheap and relatively easily scratched and faded plastic in front of our headlights.
Besides the potential for reduced luminosity when those plastic lenses becomes fogged and pitted, there's the fact that they plain look bad when they've aged poorly. Those headlight lenses have to shine with the same gleam of the windshield or the plastic will draw eyes right to their shabby, second-rate impression of "clear" and degrade the forward presentation your auto-ego depends on. Fortunately, there are a few methods to bring the clarity back to all but the most toasted clear plastic lenses and, combined with choice regenerative chemicals, you might just be back to shiny and like-new.
Buff With Your Elbow
Our first approach was a combination of old-fashioned elbow grease and a mild plastic polish designed particularly for clear plastics like the lenses we're working on now. After some enthusiastic rubbing (more strokes, not more pressure), the bulk of the minor pocks and ticks in the plastic had decreased, if not disappeared, and the haze had gone. This initial approach was essentially three separate efforts, going over each lens three times. We used a non-abrasive microfiber towel, though 100-percent cotton also works nicely, making sure to avoid getting this polish on already waxed painted surfaces or rubber parts.
Theory Here?Please Absorb
Arguments persist as to the best motion to employ when hand-buffing paint or plastic, with two camps essentially divided between the rotary "wax on, wax off" method, and the straight-line method with limited rotation. While you've all seen the typical "I just learned to do this" swirly marks on the sides of some unfortunate car (result of the wax-on method), it's likely due to misuse of the process. Poorly selected towels (woven with abrasive materials), too much rubbing pressure, not enough wax or polish on the applicator (which must be lightly dampened), improper polish selection, or working on a dirty car are all good examples resulting in bad work.
The lateral stroke pattern is supposed to alleviate the pitfalls of rotary waxing, but can cause straight scratches instead due to the same reasons that will flaw the rotary process. Also, straight-line rubbing might fail to improve linear scratches if you're not rubbing against their grain. Personal experience lends credibility to the need to select the best towels and applicators, use plenty of medium (whatever chemical you're working with) and employ both straight-line rubbing (when approaching scratches from an oblique angle) in combination with delicate wax-on action.
You have to wash the car first. Whether you're waxing or polishing (in case you don't understand, waxing is the act of filling and coating, while polishing is the use of any degree of abrasive), any substances on the surface that you didn't invite will scratch while you rub. And don't be afraid to wipe down surfaces like the plastic lens with a detailer between attacks, to keep invading substances to a minimum. We've also found automotive clay bar treatments effective on plastic, so you may run clay over the lens too-it's very effective at removing extra-stuck surface contamination.
Rub with More Grit
Our second plastic-bufftastic attack involved a more assertive polish, using a product we will not name since its maker's intended purpose does not include plastics. That said, if you talk to the folks who created the medium and exert due diligence, whether or not a polish is plastic-friendly will be readily evident. Always test the polish on a small portion of the lens anyway, just to make sure. With this second polish, a little more spark came to the clear plastic, but the nicks and dings left by the first polish used were still there. What next?
A little garage brainstorming led us to our third and final approach: add heat. It's not about whipping out a torch here, but the introduction of a small amount of warmth that could minutely soften the edges of nicks in the plastic, which are the part of the nick you see. Wear down the edges in a scratch and the scratch virtually disappears. It's the same principal employed when polishing car paint, as you want to eliminate the grabby visual cue in the scratch-its edges. Anyway, we whipped out the power wheel and went to town, slowly. A few RPM at a time, a little pressure at a time (never leaning into the buffer, as that's instant death for plastic or paint) and a good dose of the mildest plastic polish-and the remaining marks in the clear lens plastic began to fade. This is good. We are paranoid as to the overall peril to the plastic posed by an aggressive device like the buffer, though, so we did only a small bit of work with it before putting the device down for the afternoon. Without perfect light and surplus patience, this method could turn on us in a hurry, so it's back for a few minutes tomorrow when we're reassured the wheel is golden. This time we used a foam disc, too, so perhaps it's a cotton pad tomorrow.
Remember, sometimes your lenses are just beyond saving. Plastics are affected by ultraviolet and environmental eradication, and their resilience is thusly decreased, opening them up to suffer more damage from the same abuse. Even the best-maintained covers will eventually wear out. If you've been caring for them from the get-go, it'll take longer than you'll own the vehicle, but some plastics don't last. Pitting, fading that goes deeper than the surface, yellowing, or cracked, brittle plastic all signal it's time for new plastic. You just might not be able to fix them this time, but you can make a good effort with the tricks here.
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